Frequency of anisometropia in children and adolescents

Amélia F Nunes; Maria Batista; Pedro Monteiro

doi:10.12688/f1000research.73657.1

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Research Article

Frequency of anisometropia in children and adolescents

[version 1; peer review: 2 approved with reservations]

Amélia F Nunes ^1-4, Maria Batista^1,3,4, Pedro Monteiro^1-4

PUBLISHED 01 Nov 2021

Author details Author details

¹ Universidade da Beira Interior, Portugal, Covilhã, Portugal
² Health Sciences Research Centre (CICS-UBI), Universidade da Beira Interior, Covilhã, Portugal
³ UBIMedical, Universidade da Beira Interior, Covilhã, Portugal
⁴ Clinical and Experimental Center in Vision Sciences (CCECV), Universidade da Beira Interior, Covilhã, Portugal

Amélia F Nunes
Roles: Conceptualization, Data Curation, Formal Analysis, Investigation, Methodology, Project Administration, Resources, Software, Supervision, Validation, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

Maria Batista
Roles: Data Curation, Formal Analysis, Investigation, Resources, Writing – Original Draft Preparation

Pedro Monteiro
Roles: Conceptualization, Methodology, Project Administration, Supervision, Validation, Visualization, Writing – Review & Editing

OPEN PEER REVIEW

REVIEWER STATUS

Abstract

Background: Our objective was to estimate the frequency of anisometropia at various educational stages, from pre-school to 9th school year, studying its association with gender, study cycle and area of residence.
Methods: 749 children and adolescents (from 3 to 16 years old) participated in this study, 46.7% girls and 42.7% living in a rural environment. The refraction was performed with a paediatric, open field autorefractometer (PlusOptix), without cycloplegic and under binocular conditions.
Results: The frequency rate of anisometropia in the studied sample was 6.1%, varying from 2.9% in pre-school education to 9.4% in the 3rd study cycle. Myopic anisometropia was the most frequent and hyperopic and astigmatic anisometropia showed identical proportions of occurrence. No statistical evidence was found to state that the occurrence of anisometropia differs between genders or between areas of residence. Regarding the school cycle, a significant association was found with spherical equivalent anisometropia, with an increase in its frequency with school progress (p=0,012), with myopic anisometropia being the main contributor to this variation.
Conclusions: The increase in workload for near tasks has been identified as a risk factor for the increase in myopia. This fact may be related to the increase in anisometropia with the educational stage, found in this study. The high rate of anisometropia found in adolescents (9.4%) as well as the progressive increase in this rate throughout school progress (from 2.9% to 9.4%) suggests the need to extend the detection strategies of this condition to beyond childhood.

Keywords

Pediatrics, Child, Teenager, Refraction, School vision

Corresponding author: Amélia F Nunes

Competing interests: No competing interests were disclosed.

Grant information: The author(s) declared that no grants were involved in supporting this work.

Copyright: © 2021 Nunes AF et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Nunes AF, Batista M and Monteiro P. Frequency of anisometropia in children and adolescents [version 1; peer review: 2 approved with reservations]. F1000Research 2021, 10:1101 (https://doi.org/10.12688/f1000research.73657.1) First published: 01 Nov 2021, 10:1101 (https://doi.org/10.12688/f1000research.73657.1) Latest published: 08 Jun 2022, 10:1101 (https://doi.org/10.12688/f1000research.73657.4)

Introduction

Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.¹ This condition can occur in situations of myopic, hyperopic or astigmatic asymmetry and is strongly associated with the development of other eye changes such as aniseiconia, amblyopia, diplopia and strabismus.²^,³

Although there is no uniformly defined dioptre value for its clinical classification, an IOD in the spherical equivalent (SE) of 1 diopter or more is accepted as the threshold, for most authors.¹^,⁴^–⁸ However, even using this limit, the scientific literature presents a significant variation in the prevalence values of anisometropia in terms of age, gender and ethnicity.⁴^,⁵^,⁸^,⁹ Factors associated with lifestyle and educational level have also been referred to as risk factors for anisometropia.⁷^,⁸^,¹⁰

Early detection and early treatment is crucial to prevent permanent visual loss. Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation,¹¹ the early correction of anisometropia is important, either because it prevents the development of other changes such as aniseikonia, amblyopia and strabismus,³^,¹²^,¹³ and even in small degrees (<1D) facilitates emmetropization,¹¹ whether because it improves quality of life, reducing or eliminating symptoms of visual discomfort. In this way, visual screening at a young age is useful in identifying who is most likely to benefit from early optical correction or preventive treatment.¹¹^,¹⁴^,¹⁵

The clinical methods used to characterize anisometropia are refractive techniques, with autorefraction, using Plusoptix, one of the most recommended techniques for screening activities.¹⁶^,¹⁷ This instrument allows quantifying the refractive error in open field, simultaneously in both eyes and under the same conditions, in a fast, easy, safe, non-invasive way, in which it is possible to obtain a very similar value to that obtained by cycloplegic refraction¹⁷^–¹⁹ and with excellent precision in anisometropia signalling.¹⁹

Scientific studies on the prevalence of anisometropia focus on children or adults, with less research being found in adolescence. There is evidence that lifestyle, as well as educational level, may be risk factors for its development. The aim is to estimate the frequency of anisometropia (spherical and astigmatic) and to analyse its pattern of variation in a sample of children and adolescents, from preschool education (from three to six years old) to the various cycles of basic education (from the 1st to the 9th school year in Portugal, from six to fifteen years old).

Methods

749 children and adolescents aged between three and sixteen years participated. Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.

The refractive error was obtained with the paediatric autorefractometer model A09 by PlusOptix by the average of three consecutive measurements, binocular and without the use of a cycloplegic. The PlusOptix allows measuring the refractive error in real time and in both eyes at the same time, at a distance of one meter from the subject's eyes.

Data analysis

In order to calculate the average of the three refractive measurements, the power was converted from its spherical-cylindrical to its vector representation, described by Thibos,²⁰ using the following expressions:

(1)

SE = S + \frac{C}{2}

(2)

J_{0} = (- \frac{C}{2}) cos (2 α)

(3)

J_{45} = (- \frac{C}{2}) sin (2 α)

Where SE represents the spherical equivalent; J₀ represents Jackson's crossed cylinders on the 90° or 180° axis, J₄₅ represents Jackson's crossed cylinders on the 45° or 135° axis, S, C and α represent the spherical, cylindrical and cylinder axis component, respectively, of the autorefractometer measurement.

Refractive state classification

The participants were classified in emmetropes, myopes, hyperopes, astigmats or anisometropes, according to the average value of the autorefractometer. In order to carry out this classification, the criteria recommended for the autorefractometer used were applied (Table 1).

Table 1. Classification criteria for refractive state [17] 16.

Refractive state	< 6 years old	≥6 years old
Emmetrope	−1.00D < SE < +1.25D	−1.00D < SE < +1.00D
Myope	SE≤−1.00D
Hyperope	SE≥+1.25D	SE≥+1.00D
Astigmat	\|C\|≥1.00D	\|C\|≥1.25D
Anisometrope	\|IOD\|≥1.25 (SE or C)

Anisometropia classification

The absolute value of IOD of the refractive error in terms of SE was designated as spherical anisometropia (SA), the absolute IOD in astigmatism was designated as meridional anisometropia (MA) and the absolute IOD only in the astigmatic component was designated by simple meridional anisometropia (sMA), according to the cutoff points referred to in Table 1. The presence of at least one of the previous conditions was designated as total anisometropia (TA). Low anisometropia was considered for IOD values below 2.00D, high anisometropia for values between 2.00D and 6.00D and very high anisometropia for IOD values above 6.00D.

According to the type of refractive error, anisometropia was classified as myopic, when both eyes were myopic or when one eye was myopic and the other was emmetropic; hyperopic, when both eyes were hyperopic or when one eye was hyperopic and the other emmetropic; antimetropic, when one eye was myopic and the other hyperopic; simple meridional anisometropia when there was no SA, but there was MA.

Statistical analysis

A descriptive statistical analysis was carried out, using SPSS version 26 package, characterizing the sample in the variables of interest, sociodemographic and refractive, presenting means and standard deviations, frequencies and percentages both in the whole of the sample and also according to several stratifications to which it was subjected.

In all the sociodemographic factors in which the sample was categorized, groups with a large size (n > 30) were obtained and by applying the central limit theorem, it can be considered that the violation of the assumptions does not have serious consequences. Thus, the age differences between the groups were inferred by parametric tests: student’s t when the factor subdivides the sample into two groups and one way ANOVA when the factor subdivides the sample into more than two groups. To test the independence between two qualitative variables, the Chi-square independence test was applied.

All the results of the statistical inference tests were interpreted to a 95% confidence level, that is, the significance level of 0.05 was used.

Ethics approval

This study was conducted in accordance with that the principles of the Declaration of HELSINKI and written informed consent were obtained from parents of each participant in the study. It was approved by the Ethics Committee from Universidade da Beira Interior (CE-UBI-Pj-2019-043).

Consent to participate

Written informed consent was obtained from parents or legal gardians of all participants.

Results

Sample characterization

In Portugal the compulsory education includes basic education, which is divided into 3 cycles, followed by the secondary education. The 1^st cycle of basic education includes the 1^st to 4^th school year (ages 6 to 10), the 2^nd cycle includes the 5^th and 6^th year (ages 10 to 12) and the 3^rd cycle includes the 7^th to the 9^th year (ages 12 to 15). The sample under study had students from preschool to the 3^rd cycle of basic education and was characterized according to gender, area of residence and cycle of studies. Table 2 summarizes the characteristics of the sample.

Table 2. Sample characteristics.

Factor		Sample dimension N (%)	Age
Factor		Sample dimension N (%)	Average ± SD	Statistical test
Total sample		749 (100%)	9.6 ± 3.3	---
Gender	Male	399 (53.3%)	9.7 ± 3.2	t₍₇₄₇₎ = 0.903; p = 0.367
Gender	Female	350 (46.7%)	9.5 ± 3.5	t₍₇₄₇₎ = 0.903; p = 0.367
Residence area	Rural	320 (42.7%)	9.8 ± 3.3	t₍₇₄₁₎ = 1.662; p = 0.097
	Urban	423 (56.5%)	9.4 ± 3.3	t₍₇₄₁₎ = 1.662; p = 0.097
	Missing	6 (0.8%)	---	---
Study stage	Preschool	103 (13.8%)	4 ± 0.9	F_(3;745) = 2177.4; p < 0.001**
	1^st cycle	231 (30.8%)	7.6 ± 1.2
	2^nd cycle	181 (24.2%)	10.6 ± 0.9
	3^rd cycle	234 (31.2%)	13.2 ± 1.1

** Significant at the 0.01 level.

It can be seen that the sample has a similar average age between genders and between area of residence, but as can be expected, ages differ between study cycles, being higher in more advanced cycles, and this difference is statistically significant.²⁷

Refractive state

According to the classification criteria previously defined for the classification of refractive state, it was concluded that in the study sample 71.16% (n = 533) is emmetropic. Among subjects with significant refractive error (n = 216), it was found that hyperopia is the most frequent refractive error (50.5%, corresponding to 14.6% in the studied population) followed by myopia (22.7%, corresponding to 6.5% in the population), anisometropia (21.3%, corresponding to 6.1% in the population) and astigmatism (11.6% (n = 25) where 5.6% are cases of simple astigmatism and 6% compound astigmatism, corresponding to 3.3% in the population). Figure 1 shows graphically the distribution of the different refractive states in the study sample. The representation of astigmatism, refers only to the occurrence of simple astigmatism, without a significant SE.

Figure 1. Refractive error distribution.

Anisometropia

46 participants with anisometropia were identified (6.1% of the studied population). According to the magnitude of the refractive error, no child was found with very high anisometropia, 15 were registered with high anisometropia and 31 with low anisometropia, that is, of the anisometrope subjects, most (67.4%) had low anisometropia.

In the classification of anisometropia according to the type of refractive error, 37 subjects (80.4% of anisometropes, corresponding to 4.9% in the studied population) were found with SA, integrating 21 with myopia, 15 with hyperopia and 1 with antimetropia; and 15 subjects (32.6% of the anisometrope sample, corresponding to 2% in the population) with MA, and only 9 of these did not have SA, and it can be considered that about 20% of the anisometrope sample presents simple meridional anisometropia (sMA). This distribution is represented graphically in Figure 1. It is possible to observe that myopic anisometropia is the most frequent (46%), followed by hyperopic anisometropia (33%) and sMA (19%). Antimetropic anisometropia is the least frequent (2%).

Influence of sociodemographic variables

The proportion of subjects with anisometropia was analysed according to gender, area of residence and school cycle, and through the Chi-square test it was evaluated whether these variables are associated with the occurrence of anisometropia in the studied population (Table 3). The Chi-square test indicates that there is no association between sMA and any of the factors under analysis, therefore this parameter is not in the table.

Table 3. Relationship of gender, area of residence and study cycle, in anisometropia.

TA – all anisometropia (spherical and meridional); SA - spherical anisometropia. The highest rates are shown in bold.

	Gender				Chi-square test
	Female (350)		Male (399)		Chi-square test
	N	%	N	%	χ²	P
TA	25	7.1	21	5.3	1.143	0.285
SA	21	6	16	4	1.572	0.21

	Area of residence				Chi-square test
	Rural (320)		Urban (423)		Chi-square test
	N	%	N	%	χ²	P
TA	22	6.8	23	5.4	0.622	0.416
SA	18	5.6	18	4.3	0.741	0.389

	School Stage								Chi-square test
	Preschool (103)		1^st cycle (231)		2^nd cycle (181)		3^rd cycle (234)		Chi-square test
	N	%	N	%	N	%	N	%	χ²	P
TA	3	2.9	10	4.3	11	6.1	22	9.4	7.495	0.058
SA	1	1.0	9	3.9	7	3.9	20	8.6	10.918	0.012*

* Significant at the 0.05 level.

No significantly different occurrence of anisometropia was found according to gender or area of residence. (p > 0.05), however, in relation to the school, there is a pattern of variation that increases with the cycle of studies, ranging from 2.9% in preschool education to 9.4% in the 3^rd cycle of studies, however this association is only statistically significant for SA (χ²₍₃₎ = 10.918; p = 0.012), where there is a rate of 1% in preschool education and 8.6% in the 3^rd cycle. It should be noted that the study cycle is dependent on age, as shown in Table 2, older children attend the more advanced study cycle.

Figure 2 illustrates the distribution of anisometropia according to the type of refractive error, for each school cycle. It is observed that myopic anisometropia is present in all study cycles, registering a considerable increase from the beginning of school, that is, from the 1st cycle to the 3rd cycle. On the other hand, hyperopic anisometropia was manifested on a larger scale in children of the 1st cycle, with a lower occurrence in the following cycles. As for the simple MA, it is present in all study cycles and there is no specific pattern in its variation with the study cycle progress.

Figure 2. Relative frequency of the variation of the various types of anisometropia, with the school cycle.

Discussion

The present study was carried out with students, including students from preschool education (three years old) to the 9^th school year (~fifteen years old) and the value of the IOD considered was ≥1.25D, as it is the suggested value for the interpretation of the results obtained with the material used. An anisometropia rate of 6.1% was found, considering the spherical and meridional anisometropia. It was found that this rate varies with the cycle of studies, showing an increase as the level of education advances, ranging from 2.9% in preschool education to 9.4% in the 3^rd cycle of basic education and no statistically significant differences were found in the distribution of anisometropia either between genders or between areas of residence. It was also found that myopic anisometropia was the most prevalent (46%), with a considerable increase in the 3^rd cycle of studies.

Comparing with others studies, some authors point to a frequency similar to the one found on this research,⁴^,⁷^,⁸^,¹¹^,²¹ others point to a lower frequency²² and others still refer to a higher frequency.²³^,²⁴ Studies that included only children aged five and six years report rates of 1.3% and 1.6% (SA).⁵^,²⁵ The frequency of SA, found in the present study, in preschool education (children from three to six years old) was 1%, this value being closer to those studies. Others studies included participants from 15 to 19 years old and report rates of 11,2% for SA.²⁴ For the 3^rd cycle of studies (average between 12 and 15 years of age), the present study indicates a frequency of 8.6% (SA) and according to the observed variation pattern, at a more advanced age and school stage, a higher rate is expected.

Geographical and methodological issues make it difficult to compare prevalence studies. There is a pattern of greater variability in studies on the Asian continent, where for an identical age group, there are records ranging from 2.5%²² to more than 10%;⁷ however this is the continent where more studies on the subject are found. In Europe, more similar results are found, 4,6% and 6,9%.⁴^,¹¹

In the literature, the pattern of variation of anisometropia as a function of age and during the school period is not clear, presenting discordant results. Although many studies focus on children, it is common to have relatively wide age ranges. Most authors conclude that anisometropia varies with age,⁴^,⁵^,⁷^,²⁶ although there are also studies where this relationship has not been found.¹⁰^,¹³ Studies on the subject, at school age, which showed an increasing prevalence with age were carried out in populations with a high frequency of myopia, a condition whose prevalence increases in adolescence.²⁶ On the other hand, longitudinal studies show that the prevalence of anisometropia increases after children start attending school.⁵^,⁷^,²¹ Given these two lines that justify the variation of anisometropia during school age, it appears that they are related to each other, since the progress in the school path is accompanied by increasing age. In the present study, an anisometropia frequency was also found to increase with advancement in the level of education, and consequently the age factor is also contributing to this situation, with myopic anisometropia being the one that most contributes to this variation pattern.

Regarding the influence of gender on anisometropia, contradictory data are found in the scientific literature, while in one study it is reported that the prevalence found was higher in males²⁶ in others it is reported that the prevalence rates are higher in females.¹⁰^,²⁴ The results of the present study reveal a higher frequency in females (7.1%) than in males (5.3%), however these differences are not statistically significant, and this finding is in line with the results of other authors.⁹^,¹³^,²¹^,²⁵

The influence of living in rural or urban areas has also been the object of study by several researchers, considering the development of myopia and, consequently, myopic anisometropia, which is more pronounced in urban areas.⁷^,⁸^,¹⁰ The present study did not prove whether the area of residence and the frequency of anisometropia are related. This parameter is highly dependent on the way in which each author classifies the area of residence, as rural or urban, and the limits of these regions are sometimes difficult to define. Also, living in a rural area and working in an urban area means that the daily experience of some populations turns out to be more urban, in both environments.

This study has several strengths. The study was carried out in children and adolescents in a school environment, which allows minimizing the potential bias that occurs in the sampling process and avoids overestimation of the problem when the investigation is carried out in a clinical environment. For this study, spherical anisometropia and astigmatic anisometropia were considered, the latter being disregarded in several studies and there is a record that this anisometropia is the one that most varies in terms of ethnicity.⁹

Certain limitations can be pointed out in this study. Firstly, the use of autorefraction without cycloplegia is highlighted, which is not the gold standard method of refraction. This fact limits the analysis of the distribution of the different types of refractive errors found in the population studied, because despite the use of an open field autorefractometer, recognized as an instrument with good agreement with cycloplegic retinoscopy and which eliminates the need for cycloplegia in children¹⁷^,¹⁸ tends to underestimate hyperopia.¹⁷^,¹⁹ However, for the present study, this situation does not weaken the conclusions, as the refraction was evaluated in an open field and binocularly, both eyes are exposed to the same conditions, in addition to that studies by other authors with the same methodology, point out a sensitivity 100% for the diagnosis of anisometropia.¹⁹ Secondly, the choice of the cut-off point for the classification of anisometropia is pointed out, which on the one hand, the literature recommends considering an IOD of at least 1.00D, the sensitivity studies of the autorefractometer used, recommend considering 1.25D.¹⁶ Thirdly, the signalling of the area of residence of the participants as rural or urban is reported, since the limits of these regions were at times difficult to define, noting also that being a study carried out in an area of the inner country, whose territorial classification is of low density, it is expectable that habits and behaviours are more uniform between rural and urban areas, than if the same study had been carried out in an area of greater population density.

Conclusions

The present study estimates the frequency of anisometropia in Portuguese children from preschool to the 3^rd cycle of basic education finding an occurrence rate of 6.1%. The results of this work also show that the level of the study cycle and the spherical anisometropia are related, verifying that it is low in preschool education and higher in the 3^rd cycle of basic education. It was also found that, hyperopic anisometropia is more frequent in younger children and that with the progress of the school path, myopic anisometropia predominates. Taking into account the high frequency of anisometropia found in 3^rd cycle students, we are of the opinion that the performance of visual screening at this age is essential for the timely detection and correction of possible eye problems and that, consequently, will lead to better development, learning and school outcomes at these ages, which is why it is important to extend screening actions beyond childhood.

Data availability

Underlying data

Dryad: Portuguese Children Refractive data - VER+ Project, https://doi.org/10.5061/dryad.h44j0zpm5.²⁷

This project contains the following underlying data:

‐ PortugueseChildrenRefractiveDataVERmaisProjectV2.xlsx

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC0 1.0 Public domain dedication).

Acknowledgments

To Rafaela Venâncio for the support and help in data collection. To the Vision Sciences Clinical and Experimental Centre and UBImedical for the availability of the equipment used and to the Beira Interior University Mission Group in Optometry and Vision Sciences for encouraging this study.

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27. Nunes AF, Batista MJ, Monteiro PL: Portuguese Children Refractive data - VER+ Project.2021. Publisher Full Text

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Version 4

VERSION 4 PUBLISHED 01 Nov 2021

Author details Author details

Maria Batista
Roles: Data Curation, Formal Analysis, Investigation, Resources, Writing – Original Draft Preparation

Pedro Monteiro
Roles: Conceptualization, Methodology, Project Administration, Supervision, Validation, Visualization, Writing – Review & Editing

Competing interests

No competing interests were disclosed.

Grant information

The author(s) declared that no grants were involved in supporting this work.

Article Versions (4)

version 4

Revised

Published: 08 Jun 2022, 10:1101

https://doi.org/10.12688/f1000research.73657.4

version 3

Revised

Published: 10 Jan 2022, 10:1101

https://doi.org/10.12688/f1000research.73657.3

version 2

Revised

Published: 08 Dec 2021, 10:1101

https://doi.org/10.12688/f1000research.73657.2

version 1

Published: 01 Nov 2021, 10:1101

https://doi.org/10.12688/f1000research.73657.1

© 2021 Nunes AF et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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CITE

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Nunes AF, Batista M and Monteiro P. Frequency of anisometropia in children and adolescents [version 1; peer review: 2 approved with reservations]. F1000Research 2021, 10:1101 (https://doi.org/10.12688/f1000research.73657.1)

NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.

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Open Peer Review

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VERSION 1

PUBLISHED 01 Nov 2021

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Reviewer Report 19 Nov 2021

Pedro M. Serra, Research and Development Department, Ophthalmology Clinic Vista Sánchez Trancón, Badajoz, Spain

Approved with Reservations

https://doi.org/10.5256/f1000research.77322.r98419

General comment

Thank you for considering my name as a reviewer of the manuscript titled “Frequency of anisometropia in children and adolescents”. I would like to congratulate the authors for their work in this field of vision sciences which has a special interest in countries where is a shortage of epidemiologic data in the field of vision.
Regarding the manuscript, my feeling is that it requires additional work before it is considered for indexing. In this report I will cover the technical issues that in my opinion would improve the quality of the manuscript, however, I would recommend the author's linguistic editing of the final manuscript. Examples of linguistic improvement are very long sentences with multiple ideas and some lack of concise writing.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)
How did you build the sample?
Describe the dependent and independent variables
Remove any data from the methods

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic
“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.
2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it
4^th paragraph- describes the instrument used. I would suggest moving this information to the methods
5^th paragraph- states the aim of the study.
Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

Methods:

Please include:

Type of study
Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?
Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.
Duration of the study (e.g September 2021 – November 2021)
Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

Instrument description

Include PlusOptix manufacturer city and country
Provide the repeatability of the instrument (published)

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.
Say that the Cylinder component needs to be in negative form

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.
Refractive State
- Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation and range
- Figure 1 has limited information, I suggest including the percentages in the table mentioned above
Anisometropia
- Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)
- Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range
- Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.
Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects in risk of developing amblyopia.

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Vision Sciences, Ophthalmic Optics.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

CITE

Report a concern

Author Response 08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

08 Dec 2021

Author Response
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. ... Continue reading
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. We updated the article according to your comments.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

R: The abstract was modified to include the topic and the aims “This research was developed to study the epidemiology of anisometropia. It aims to estimate the prevalence of anisometropia in Portuguese children and adolescents at various educational stages, studying its association with sociodemographic variables”

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)

How did you build the sample?

Describe the dependent and independent variables

Remove any data from the methods

R: All information was included and data was removed. The sample was collected from several kindergartens and schools in the central region of Portugal. The central region was included in the abstract and more details were added to the methods section.

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

R: Section changed

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

R: Section changed

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic

“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.

2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it

4^th paragraph- describes the instrument used. I would suggest moving this information to the methods

5^th paragraph- states the aim of the study.

Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

R: All information was included. A new table (new table 1) was introduced containing prevalence studies. We did not find any studies regarding anisometropia prevalence in Portugal, in indexed research papers. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Methods:

Please include:

Type of study

Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?

Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.

Duration of the study (e.g September 2021 – November 2021)

Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

R: This information is important and was included to some extent in the methods section. Rural and Urban definitions were based on the information provided by the municipalities representative.

Instrument description

Include PlusOptix manufacturer city and country

Provide the repeatability of the instrument (published)

This is just a comment - “ Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.”
This is probably one of the most valuable pieces of information from the data collection and it is a shame not being presented.

R: Information included. Although a study reports repeatability of around 0,6D for MSE with the A09 model (Plusoptix Vision Screener: the accuracy and repeatability of refractive measurements using a new autorefractor) this and other studies are not focused on anisometropia, for which IOD MSE errors could be minimized. Another study with a different plus optix model, reports a sensitivity of 100% for anisometropia (A comparison of plusoptiX A12 measurements with cycloplegic refraction). We included this study in the introduction.

Data Analysis

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.

Say that the Cylinder component needs to be in negative form

R: This information has been added

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

R: The formulas were added

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.

R: Paragraph moved

Refractive State

Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation, and range

Figure 1 has limited information, I suggest including the percentages in the table mentioned above

R: A new table (table 4) containing this data was added to this section

Anisometropia

Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)

Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range

Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

R: Sentence rewritten
Mean, standard deviation, and range of anisometropia per type was added in table 4. An extra figure would duplicate the information.
Information about the age group is already included in table 5, distributed by the study cycle which indirectly represents age groups. An extra figure would duplicate the information.

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.

R: This is an excellent suggestion for future research. We can hypothesise that an excess of near-work activities, associated with incorrect posture, can lead to asymmetric eye growth. However, those factors were not controlled in the present study.

Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects at risk of developing amblyopia.

R: Only 2 uncorrected anisometropes were hyperopic, and since no BCVA data was collected, we feel that there are no sufficient data to support this kind of analysis. However, we agree that it is an excellent suggestion for future work.
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. We updated the article according to your comments.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

R: The abstract was modified to include the topic and the aims “This research was developed to study the epidemiology of anisometropia. It aims to estimate the prevalence of anisometropia in Portuguese children and adolescents at various educational stages, studying its association with sociodemographic variables”

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)

How did you build the sample?

Describe the dependent and independent variables

Remove any data from the methods

R: All information was included and data was removed. The sample was collected from several kindergartens and schools in the central region of Portugal. The central region was included in the abstract and more details were added to the methods section.

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

R: Section changed

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

R: Section changed

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic

“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.

2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it

4^th paragraph- describes the instrument used. I would suggest moving this information to the methods

5^th paragraph- states the aim of the study.

Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

R: All information was included. A new table (new table 1) was introduced containing prevalence studies. We did not find any studies regarding anisometropia prevalence in Portugal, in indexed research papers. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Methods:

Please include:

Type of study

Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?

Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.

Duration of the study (e.g September 2021 – November 2021)

Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

R: This information is important and was included to some extent in the methods section. Rural and Urban definitions were based on the information provided by the municipalities representative.

Instrument description

Include PlusOptix manufacturer city and country

Provide the repeatability of the instrument (published)

This is just a comment - “ Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.”
This is probably one of the most valuable pieces of information from the data collection and it is a shame not being presented.

R: Information included. Although a study reports repeatability of around 0,6D for MSE with the A09 model (Plusoptix Vision Screener: the accuracy and repeatability of refractive measurements using a new autorefractor) this and other studies are not focused on anisometropia, for which IOD MSE errors could be minimized. Another study with a different plus optix model, reports a sensitivity of 100% for anisometropia (A comparison of plusoptiX A12 measurements with cycloplegic refraction). We included this study in the introduction.

Data Analysis

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.

Say that the Cylinder component needs to be in negative form

R: This information has been added

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

R: The formulas were added

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.

R: Paragraph moved

Refractive State

Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation, and range

Figure 1 has limited information, I suggest including the percentages in the table mentioned above

R: A new table (table 4) containing this data was added to this section

Anisometropia

Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)

Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range

Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

R: Sentence rewritten
Mean, standard deviation, and range of anisometropia per type was added in table 4. An extra figure would duplicate the information.
Information about the age group is already included in table 5, distributed by the study cycle which indirectly represents age groups. An extra figure would duplicate the information.

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.

R: This is an excellent suggestion for future research. We can hypothesise that an excess of near-work activities, associated with incorrect posture, can lead to asymmetric eye growth. However, those factors were not controlled in the present study.

Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects at risk of developing amblyopia.

R: Only 2 uncorrected anisometropes were hyperopic, and since no BCVA data was collected, we feel that there are no sufficient data to support this kind of analysis. However, we agree that it is an excellent suggestion for future work.
Competing Interests: No competing interests. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

08 Dec 2021

Author Response
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. ... Continue reading
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. We updated the article according to your comments.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

R: The abstract was modified to include the topic and the aims “This research was developed to study the epidemiology of anisometropia. It aims to estimate the prevalence of anisometropia in Portuguese children and adolescents at various educational stages, studying its association with sociodemographic variables”

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)

How did you build the sample?

Describe the dependent and independent variables

Remove any data from the methods

R: All information was included and data was removed. The sample was collected from several kindergartens and schools in the central region of Portugal. The central region was included in the abstract and more details were added to the methods section.

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

R: Section changed

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

R: Section changed

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic

“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.

2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it

4^th paragraph- describes the instrument used. I would suggest moving this information to the methods

5^th paragraph- states the aim of the study.

Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

R: All information was included. A new table (new table 1) was introduced containing prevalence studies. We did not find any studies regarding anisometropia prevalence in Portugal, in indexed research papers. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Methods:

Please include:

Type of study

Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?

Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.

Duration of the study (e.g September 2021 – November 2021)

Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

R: This information is important and was included to some extent in the methods section. Rural and Urban definitions were based on the information provided by the municipalities representative.

Instrument description

Include PlusOptix manufacturer city and country

Provide the repeatability of the instrument (published)

This is just a comment - “ Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.”
This is probably one of the most valuable pieces of information from the data collection and it is a shame not being presented.

R: Information included. Although a study reports repeatability of around 0,6D for MSE with the A09 model (Plusoptix Vision Screener: the accuracy and repeatability of refractive measurements using a new autorefractor) this and other studies are not focused on anisometropia, for which IOD MSE errors could be minimized. Another study with a different plus optix model, reports a sensitivity of 100% for anisometropia (A comparison of plusoptiX A12 measurements with cycloplegic refraction). We included this study in the introduction.

Data Analysis

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.

Say that the Cylinder component needs to be in negative form

R: This information has been added

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

R: The formulas were added

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.

R: Paragraph moved

Refractive State

Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation, and range

Figure 1 has limited information, I suggest including the percentages in the table mentioned above

R: A new table (table 4) containing this data was added to this section

Anisometropia

Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)

Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range

Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

R: Sentence rewritten
Mean, standard deviation, and range of anisometropia per type was added in table 4. An extra figure would duplicate the information.
Information about the age group is already included in table 5, distributed by the study cycle which indirectly represents age groups. An extra figure would duplicate the information.

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.

R: This is an excellent suggestion for future research. We can hypothesise that an excess of near-work activities, associated with incorrect posture, can lead to asymmetric eye growth. However, those factors were not controlled in the present study.

Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects at risk of developing amblyopia.

R: Only 2 uncorrected anisometropes were hyperopic, and since no BCVA data was collected, we feel that there are no sufficient data to support this kind of analysis. However, we agree that it is an excellent suggestion for future work.
We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. We updated the article according to your comments.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

R: The abstract was modified to include the topic and the aims “This research was developed to study the epidemiology of anisometropia. It aims to estimate the prevalence of anisometropia in Portuguese children and adolescents at various educational stages, studying its association with sociodemographic variables”

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)

How did you build the sample?

Describe the dependent and independent variables

Remove any data from the methods

R: All information was included and data was removed. The sample was collected from several kindergartens and schools in the central region of Portugal. The central region was included in the abstract and more details were added to the methods section.

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

R: Section changed

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

R: Section changed

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic

“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.

2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it

4^th paragraph- describes the instrument used. I would suggest moving this information to the methods

5^th paragraph- states the aim of the study.

Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

R: All information was included. A new table (new table 1) was introduced containing prevalence studies. We did not find any studies regarding anisometropia prevalence in Portugal, in indexed research papers. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Methods:

Please include:

Type of study

Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?

Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.

Duration of the study (e.g September 2021 – November 2021)

Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

R: This information is important and was included to some extent in the methods section. Rural and Urban definitions were based on the information provided by the municipalities representative.

Instrument description

Include PlusOptix manufacturer city and country

Provide the repeatability of the instrument (published)

This is just a comment - “ Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.”
This is probably one of the most valuable pieces of information from the data collection and it is a shame not being presented.

R: Information included. Although a study reports repeatability of around 0,6D for MSE with the A09 model (Plusoptix Vision Screener: the accuracy and repeatability of refractive measurements using a new autorefractor) this and other studies are not focused on anisometropia, for which IOD MSE errors could be minimized. Another study with a different plus optix model, reports a sensitivity of 100% for anisometropia (A comparison of plusoptiX A12 measurements with cycloplegic refraction). We included this study in the introduction.

Data Analysis

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.

Say that the Cylinder component needs to be in negative form

R: This information has been added

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

R: The formulas were added

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.

R: Paragraph moved

Refractive State

Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation, and range

Figure 1 has limited information, I suggest including the percentages in the table mentioned above

R: A new table (table 4) containing this data was added to this section

Anisometropia

Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)

Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range

Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

R: Sentence rewritten
Mean, standard deviation, and range of anisometropia per type was added in table 4. An extra figure would duplicate the information.
Information about the age group is already included in table 5, distributed by the study cycle which indirectly represents age groups. An extra figure would duplicate the information.

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.

R: This is an excellent suggestion for future research. We can hypothesise that an excess of near-work activities, associated with incorrect posture, can lead to asymmetric eye growth. However, those factors were not controlled in the present study.

Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects at risk of developing amblyopia.

R: Only 2 uncorrected anisometropes were hyperopic, and since no BCVA data was collected, we feel that there are no sufficient data to support this kind of analysis. However, we agree that it is an excellent suggestion for future work.
Competing Interests: No competing interests. Close
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Reviewer Report 12 Nov 2021

Carla Costa Lança, Comprehensive Health Research Center (CHRC), Escola Nacional de Saúde Pública, Universidade Nova de Lisboa, Lisboa, Portugal; Escola Superior de Tecnologia da Saúde de Lisboa (ESTeSL), Instituto Politecnico de Lisboa, Lisbon, Lisbon, Portugal

Approved with Reservations

https://doi.org/10.5256/f1000research.77322.r98416

The study reports on the prevalence of anisometropia in a sample of Portuguese children and adolescents. The wording needs major revision. I have several comments as shown below.

Title

I suggest replacing the

The study reports on the prevalence of anisometropia in a sample of Portuguese children and adolescents. The wording needs major revision. I have several comments as shown below.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.
Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.
There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

Results

The first paragraph should be moved to the methods section.
Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).
At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).
Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.
Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p value.
Table 3 – delete the X2 value and only present p value. Non-significant p values may be presented with only 2 decimal places.
For risk factor analysis the multivariate adjusted analysis should be additionally shown.
Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

Discussion

Please, delete the 1^st sentence.
The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.
Another limitation of the study that was not referred is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.
Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Refractive errors and strabismus

CITE

Report a concern

Author Response 08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

08 Dec 2021

Author Response
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us ... Continue reading
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us to improve this document. We have made the required corrections.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

R: The title was replaced

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.

R: The word was replaced

Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

R: Sentence revised to “No statistical differences were found between genders or between areas of residence regarding the rate of anisometropia”;
Last sentence revised to “Regarding spherical equivalent anisometropia, there is a pattern of variation that increases with the cycle of studies (��²₍₃₎= 10.918; p = 0.012), with myopic anisometropia being the main contributor to this variation.”

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.

R: The first sentence was split and wording revised to:” Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.”
The third paragraph split and wording revised to:” Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation, the early correction of anisometropia is important.¹¹ This prevents the development of other changes such as aniseikonia, amblyopia and strabismus^3,12,13 and even in small degrees (<1D) facilitates emmetropization.¹¹ It also improves quality of life, reducing or eliminating symptoms of visual discomfort.”

There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

R: These data were introduced in a new table, and the reference numbering was changed accordingly.

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

R: The method section was completed including the following text “Data from the Portuguese Census 2011, shows a population of 319284 from 0 to 14 years old in the central region. For a confidence level of 95% and a 5% margin of error, taking into account that the prevalence of the studied condition is unknown, it was fixed at 50% to obtain a large enough sample size. The result was a minimum of 384 subjects. The data collection took place in 5 schools of the central region of Portugal, including all students that were authorized to participate by their legal guardians.”

Results

The first paragraph should be moved to the methods section.

R: The paragraph was moved

Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).

R: Done. This table was moved to the methods section, and the statistical analysis was deleted since it did not provide significant information.

At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).

R: Text rewritten to past tense.

Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.

R: Both sections were rewritten to avoid double percentages.

Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p-value.

R: The sentence was moved to the methods section. “Therefore..” was removed and the p-value information was added to the table.

Table 3 – delete the X2 value and only present p-value. Non-significant p values may be presented with only 2 decimal places.

R: X2 values deleted and p values with 2 decimal places

For risk factor analysis the multivariate adjusted analysis should be additionally shown.

R: The multivariate analysis was added to the table.

Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

R: Legend colour changed. Y-axis caption revised.

Discussion

Please, delete the 1^st sentence.

R: Sentence deleted

The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.

R: An extra sentence was added to explain to acknowledge the contribution of environmental factors “Some studies show that lifestyle parameters, such as reading and writing habits and time spent indoors, contribute to the prevalence of anisometropia variation. ^7,8,10,11”

Another limitation of the study that was not referred to is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.

R: We recognise the relevance of these factors, and they will be included in future studies. Accordingly to your suggestions, the following sentence was added to the end of the text “For future studies, data regarding reading habits and time spent outdoors will be collected, since these can be risk factors for the development of refractive errors.”

Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

R: This is not the first study in Portugal, however in indexed research papers we couldn’t find any comparable studies for Portugal. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

R: The sentence was revised and divided to: “Taking into account the high frequency of anisometropia found in 3^rd cycle students, in our opinion the implementation of visual screening programs at this age is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning, and school outcomes at these ages.”
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us to improve this document. We have made the required corrections.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

R: The title was replaced

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.

R: The word was replaced

Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

R: Sentence revised to “No statistical differences were found between genders or between areas of residence regarding the rate of anisometropia”;
Last sentence revised to “Regarding spherical equivalent anisometropia, there is a pattern of variation that increases with the cycle of studies (��²₍₃₎= 10.918; p = 0.012), with myopic anisometropia being the main contributor to this variation.”

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.

R: The first sentence was split and wording revised to:” Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.”
The third paragraph split and wording revised to:” Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation, the early correction of anisometropia is important.¹¹ This prevents the development of other changes such as aniseikonia, amblyopia and strabismus^3,12,13 and even in small degrees (<1D) facilitates emmetropization.¹¹ It also improves quality of life, reducing or eliminating symptoms of visual discomfort.”

There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

R: These data were introduced in a new table, and the reference numbering was changed accordingly.

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

R: The method section was completed including the following text “Data from the Portuguese Census 2011, shows a population of 319284 from 0 to 14 years old in the central region. For a confidence level of 95% and a 5% margin of error, taking into account that the prevalence of the studied condition is unknown, it was fixed at 50% to obtain a large enough sample size. The result was a minimum of 384 subjects. The data collection took place in 5 schools of the central region of Portugal, including all students that were authorized to participate by their legal guardians.”

Results

The first paragraph should be moved to the methods section.

R: The paragraph was moved

Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).

R: Done. This table was moved to the methods section, and the statistical analysis was deleted since it did not provide significant information.

At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).

R: Text rewritten to past tense.

Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.

R: Both sections were rewritten to avoid double percentages.

Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p-value.

R: The sentence was moved to the methods section. “Therefore..” was removed and the p-value information was added to the table.

Table 3 – delete the X2 value and only present p-value. Non-significant p values may be presented with only 2 decimal places.

R: X2 values deleted and p values with 2 decimal places

For risk factor analysis the multivariate adjusted analysis should be additionally shown.

R: The multivariate analysis was added to the table.

Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

R: Legend colour changed. Y-axis caption revised.

Discussion

Please, delete the 1^st sentence.

R: Sentence deleted

The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.

R: An extra sentence was added to explain to acknowledge the contribution of environmental factors “Some studies show that lifestyle parameters, such as reading and writing habits and time spent indoors, contribute to the prevalence of anisometropia variation. ^7,8,10,11”

Another limitation of the study that was not referred to is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.

R: We recognise the relevance of these factors, and they will be included in future studies. Accordingly to your suggestions, the following sentence was added to the end of the text “For future studies, data regarding reading habits and time spent outdoors will be collected, since these can be risk factors for the development of refractive errors.”

Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

R: This is not the first study in Portugal, however in indexed research papers we couldn’t find any comparable studies for Portugal. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

R: The sentence was revised and divided to: “Taking into account the high frequency of anisometropia found in 3^rd cycle students, in our opinion the implementation of visual screening programs at this age is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning, and school outcomes at these ages.”
Competing Interests: No competing interests. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

08 Dec 2021

Author Response
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us ... Continue reading
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us to improve this document. We have made the required corrections.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

R: The title was replaced

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.

R: The word was replaced

Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

R: Sentence revised to “No statistical differences were found between genders or between areas of residence regarding the rate of anisometropia”;
Last sentence revised to “Regarding spherical equivalent anisometropia, there is a pattern of variation that increases with the cycle of studies (��²₍₃₎= 10.918; p = 0.012), with myopic anisometropia being the main contributor to this variation.”

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.

R: The first sentence was split and wording revised to:” Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.”
The third paragraph split and wording revised to:” Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation, the early correction of anisometropia is important.¹¹ This prevents the development of other changes such as aniseikonia, amblyopia and strabismus^3,12,13 and even in small degrees (<1D) facilitates emmetropization.¹¹ It also improves quality of life, reducing or eliminating symptoms of visual discomfort.”

There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

R: These data were introduced in a new table, and the reference numbering was changed accordingly.

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

R: The method section was completed including the following text “Data from the Portuguese Census 2011, shows a population of 319284 from 0 to 14 years old in the central region. For a confidence level of 95% and a 5% margin of error, taking into account that the prevalence of the studied condition is unknown, it was fixed at 50% to obtain a large enough sample size. The result was a minimum of 384 subjects. The data collection took place in 5 schools of the central region of Portugal, including all students that were authorized to participate by their legal guardians.”

Results

The first paragraph should be moved to the methods section.

R: The paragraph was moved

Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).

R: Done. This table was moved to the methods section, and the statistical analysis was deleted since it did not provide significant information.

At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).

R: Text rewritten to past tense.

Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.

R: Both sections were rewritten to avoid double percentages.

Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p-value.

R: The sentence was moved to the methods section. “Therefore..” was removed and the p-value information was added to the table.

Table 3 – delete the X2 value and only present p-value. Non-significant p values may be presented with only 2 decimal places.

R: X2 values deleted and p values with 2 decimal places

For risk factor analysis the multivariate adjusted analysis should be additionally shown.

R: The multivariate analysis was added to the table.

Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

R: Legend colour changed. Y-axis caption revised.

Discussion

Please, delete the 1^st sentence.

R: Sentence deleted

The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.

R: An extra sentence was added to explain to acknowledge the contribution of environmental factors “Some studies show that lifestyle parameters, such as reading and writing habits and time spent indoors, contribute to the prevalence of anisometropia variation. ^7,8,10,11”

Another limitation of the study that was not referred to is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.

R: We recognise the relevance of these factors, and they will be included in future studies. Accordingly to your suggestions, the following sentence was added to the end of the text “For future studies, data regarding reading habits and time spent outdoors will be collected, since these can be risk factors for the development of refractive errors.”

Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

R: This is not the first study in Portugal, however in indexed research papers we couldn’t find any comparable studies for Portugal. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

R: The sentence was revised and divided to: “Taking into account the high frequency of anisometropia found in 3^rd cycle students, in our opinion the implementation of visual screening programs at this age is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning, and school outcomes at these ages.”
We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us to improve this document. We have made the required corrections.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

R: The title was replaced

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.

R: The word was replaced

Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

R: Sentence revised to “No statistical differences were found between genders or between areas of residence regarding the rate of anisometropia”;
Last sentence revised to “Regarding spherical equivalent anisometropia, there is a pattern of variation that increases with the cycle of studies (��²₍₃₎= 10.918; p = 0.012), with myopic anisometropia being the main contributor to this variation.”

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.

R: The first sentence was split and wording revised to:” Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.”
The third paragraph split and wording revised to:” Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation, the early correction of anisometropia is important.¹¹ This prevents the development of other changes such as aniseikonia, amblyopia and strabismus^3,12,13 and even in small degrees (<1D) facilitates emmetropization.¹¹ It also improves quality of life, reducing or eliminating symptoms of visual discomfort.”

There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

R: These data were introduced in a new table, and the reference numbering was changed accordingly.

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

R: The method section was completed including the following text “Data from the Portuguese Census 2011, shows a population of 319284 from 0 to 14 years old in the central region. For a confidence level of 95% and a 5% margin of error, taking into account that the prevalence of the studied condition is unknown, it was fixed at 50% to obtain a large enough sample size. The result was a minimum of 384 subjects. The data collection took place in 5 schools of the central region of Portugal, including all students that were authorized to participate by their legal guardians.”

Results

The first paragraph should be moved to the methods section.

R: The paragraph was moved

Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).

R: Done. This table was moved to the methods section, and the statistical analysis was deleted since it did not provide significant information.

At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).

R: Text rewritten to past tense.

Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.

R: Both sections were rewritten to avoid double percentages.

Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p-value.

R: The sentence was moved to the methods section. “Therefore..” was removed and the p-value information was added to the table.

Table 3 – delete the X2 value and only present p-value. Non-significant p values may be presented with only 2 decimal places.

R: X2 values deleted and p values with 2 decimal places

For risk factor analysis the multivariate adjusted analysis should be additionally shown.

R: The multivariate analysis was added to the table.

Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

R: Legend colour changed. Y-axis caption revised.

Discussion

Please, delete the 1^st sentence.

R: Sentence deleted

The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.

R: An extra sentence was added to explain to acknowledge the contribution of environmental factors “Some studies show that lifestyle parameters, such as reading and writing habits and time spent indoors, contribute to the prevalence of anisometropia variation. ^7,8,10,11”

Another limitation of the study that was not referred to is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.

R: We recognise the relevance of these factors, and they will be included in future studies. Accordingly to your suggestions, the following sentence was added to the end of the text “For future studies, data regarding reading habits and time spent outdoors will be collected, since these can be risk factors for the development of refractive errors.”

Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

R: This is not the first study in Portugal, however in indexed research papers we couldn’t find any comparable studies for Portugal. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

R: The sentence was revised and divided to: “Taking into account the high frequency of anisometropia found in 3^rd cycle students, in our opinion the implementation of visual screening programs at this age is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning, and school outcomes at these ages.”
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Version 4

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Version 3 (revision) 10 Jan 22	read
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Carla Costa Lança, Escola Nacional de Saúde Pública, Universidade Nova de Lisboa, Lisboa, Portugal; Instituto Politecnico de Lisboa, Lisbon, Portugal
Pedro M. Serra, Ophthalmology Clinic Vista Sánchez Trancón, Badajoz, Spain

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12 Jul 2023 | for Version 4

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Approved

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Refractive errors and strabismus

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13 Views

13 Jan 2022 | for Version 3

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Approved

The authors have revised the paper and addressed my previous comments. I still have 3 minor suggestions as described below.

Page 1 of 28: and page 7 of 28

Please, delete “χ2(3) = 10.918;”

Page 5 of 28:

Please, delete the final “e” from “componente”.
Please, delete “and by applying the central limit theorem, it can be considered that the violation of the assumptions does not have serious consequences."

Competing Interests

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Reviewer Expertise

Refractive errors and strabismus

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13 Views

24 Dec 2021 | for Version 2

Pedro M. Serra, Research and Development Department, Ophthalmology Clinic Vista Sánchez Trancón, Badajoz, Spain

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Approved

I would like to thank the authors for having implemented my recommendations in the current version of the manuscript. Generally, the manuscript improved considerably but it requires linguist editing.

Specific comments

Abstract:

I recommend using the word prevalent instead of “frequent”, it highlights the aim of the study.
When possible avoid passive voice “An increase in anisometropia with the educational stage, was found in this study”. May be better: This study found an increase in…

Introduction:

“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with similar sociodemographic, environmental, and genetic influences, can have asymmetric eye growth” Recommended - Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, can have asymmetric eye growth.
“Scientific studies on the prevalence of anisometropia focus on children or adults, with less research being found in adolescence, table 1. Recommended: remove the word Scientific and place table 1 in the discussion.

Methods:

I think it would be useful to indicate how rural and urban schools were segmented. For instance, say rural Schools were defined when settled in a living area with less than X thousand inhabitants.
“Only two volunteers were excluded.” Be consistent with the terminology used, participants or volunteers?
I believe Table 2 would be better placed in the results part.

Discussion

The discussion needs to have the sentences shortened and the sentences need to be more objective.

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Vision Sciences, Ophthalmic Optics.

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Author Response

10 Jan 2022

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

Thank you so much for the review. We have made the changes accordingly based on the comments.

Abstract:
I recommend using the word prevalent instead of “frequent”, it highlights the aim of the study.
Response: The wording was replaced in the abstract and in the remaining text.

When possible avoid passive voice “An increase in anisometropia with the educational stage, was found in this study”. May be better: This study found an increase in…
Response: The sentence was modified.

Introduction:
“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with similar sociodemographic, environmental, and genetic influences, can have asymmetric eye growth” Recommended - Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, can have asymmetric eye growth.
Response: The sentence was modified.

“Scientific studies on the prevalence of anisometropia focus on children or adults, with less research being found in adolescence, table 1. Recommended: remove the word Scientific and place table 1 in the discussion.
Response: The word was removed and table 1 moved to the discussion section.

Methods:
I think it would be useful to indicate how rural and urban schools were segmented. For instance, say rural Schools were defined when settled in a living area with less than X thousand inhabitants.

Response: That segmentation wasn’t done by this research team, it was provided by the municipalities representative. The following sentence was added to the sample characterization methods section “Rural and urban areas classification was based on the information provided by the municipalities, considering the residence area of each participant.”

“Only two volunteers were excluded.” Be consistent with the terminology used, participants or volunteers?

Response: The terminology was all changed to participants.

I believe Table 2 would be better placed in the results part.

Response: In the first version of the manuscript, table 2 was in the results section. However since it presented data regarding the sample characterization, the other reviewer requested that it should be moved to the methods section.

Discussion
The discussion needs to have the sentences shortened and the sentences need to be more objective.

Response: Several sentences have been changed in the discussion section.

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Reviewer Report

18 Views

10 Dec 2021 | for Version 2

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Approved

The paper is much improved, and the authors have addressed most of my comments. However, I still have a few minor comments:

Introduction: Table 1 should be moved to the discussion section. It is not common to see tables in the introduction section of scientific papers. The table needs a legend for the abbreviations mentioned.
Results: Table 5: The values of Z(adjust) do not add much to the table and the p-value is best. I suggest deleting the Z(adjust) values.
Conclusions: The authors refer that screening programmes are necessary. However, only 8 of the 46 participants did not have a correction, meaning that the majority had been already diagnosed. The conclusion needs further refinement.

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Refractive errors and strabismus

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Author Response

10 Jan 2022

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

Thank you so much for the review. We have made the changes accordingly based on the comments.

Introduction: Table 1 should be moved to the discussion section. It is not common to see tables in the introduction section of scientific papers. The table needs a legend for the abbreviations mentioned.
Response: Table 1 was moved to the discussion section (table and reference numbers will be updated)

Results: Table 5: The values of Z(adjust) do not add much to the table and the p-value is best. I suggest deleting the Z(adjust) values.
Response: Table 5, Z(adjust) deleted

Conclusions: The authors refer that screening programs are necessary. However, only 8 of the 46 participants did not have a correction, meaning that the majority had been already diagnosed. The conclusion needs further refinement.
Response: The last paragraph of the conclusion was changed to “Regarding anisometropia, 17% of the subjects were uncorrected, which can be associated to an absence of visual related symptoms due to a possible amblyopia. Taking into account the cases of uncorrected anisometropia, in our opinion the implementation of visual screening programs is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning and school outcomes.”

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

24 Views

19 Nov 2021 | for Version 1

Pedro M. Serra, Research and Development Department, Ophthalmology Clinic Vista Sánchez Trancón, Badajoz, Spain

24 Views Cite this report Responses(1)

Approved With Reservations

Indicate the study design? (e.g. Observational Cross-sectional study)
How did you build the sample?
Describe the dependent and independent variables
Remove any data from the methods

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic
“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.
2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it
4^th paragraph- describes the instrument used. I would suggest moving this information to the methods
5^th paragraph- states the aim of the study.
Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

Methods:

Please include:

Type of study
Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?
Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.
Duration of the study (e.g September 2021 – November 2021)
Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

Instrument description

Include PlusOptix manufacturer city and country
Provide the repeatability of the instrument (published)

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.
Say that the Cylinder component needs to be in negative form

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.
Refractive State
- Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation and range
- Figure 1 has limited information, I suggest including the percentages in the table mentioned above
Anisometropia
- Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)
- Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range
- Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.
Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects in risk of developing amblyopia.

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Vision Sciences, Ophthalmic Optics.

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Author Response

08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

We thank the reviewer for his time and very constructive comments. We appreciate the reviewers' voluntary contributions in the form of helpful comments that allowed us to strengthen our article. We updated the article according to your comments.

Specific topics

Abstract: Provide a statement defining the topic of research and a second sentence where you state the aim of the study (eg. This study aims to estimate the prevalence of anisometropia in the Portuguese population of children and adolescents.) I suggest changing the word frequency to prevalence throughout the text.

R: The abstract was modified to include the topic and the aims “This research was developed to study the epidemiology of anisometropia. It aims to estimate the prevalence of anisometropia in Portuguese children and adolescents at various educational stages, studying its association with sociodemographic variables”

Methods:

Indicate the study design? (e.g. Observational Cross-sectional study)
How did you build the sample?
Describe the dependent and independent variables
Remove any data from the methods

R: All information was included and data was removed. The sample was collected from several kindergartens and schools in the central region of Portugal. The central region was included in the abstract and more details were added to the methods section.

Results

Use direct messages (e.g. No association was found between the presence of anisometropia with gender or area of residence)

R: Section changed

Conclusion

The first sentence should be deleted this is not a conclusion from the present study.

R: Section changed

Introduction:

I think the introduction requires some improvement

1^st paragraph – Provides a definition of the research topic
“Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error, representing a specific refractive condition insofar as the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.” Please reformulate this sentence, particularly remove the word presumably.
2^nd paragraph and 3^rd paragraph – mention the risk factors for anisometropia and the importance of assessing it
4^th paragraph- describes the instrument used. I would suggest moving this information to the methods
5^th paragraph- states the aim of the study.
Missing information- the authors should mention the prevalence studies published, especially in Portugal, and compare with other European countries.

R: All information was included. A new table (new table 1) was introduced containing prevalence studies. We did not find any studies regarding anisometropia prevalence in Portugal, in indexed research papers. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Methods:

Please include:

Type of study
Nature of the sample, how did you select the different groups? There are differences in the socioeconomic nature of the study sites? Please indicate how did you define Rural and Urban populations? (e.g. number of inhabitants covered by each school)?
Please indicate specifically the region where this study was conducted, this is important for instance in future meta-analysis studies.
Duration of the study (e.g September 2021 – November 2021)
Could you add information about the use of spectacles, you could try to see if the anisometropia had already been identified.

R: This information is important and was included to some extent in the methods section. Rural and Urban definitions were based on the information provided by the municipalities representative.

Instrument description

Include PlusOptix manufacturer city and country
Provide the repeatability of the instrument (published)

This is just a comment - “ Students' data for which it was not possible to obtain refraction were excluded, due to technical issues associated with the performance of the instrument (presence of strabismus, opacities, retinal anomalies or when the refractive error exceeded the instrument's measurement limit - spherical measurement range or cylindrical from −7.00 to +5.00D) or due to lack of cooperation from the participant.”
This is probably one of the most valuable pieces of information from the data collection and it is a shame not being presented.

R: Information included. Although a study reports repeatability of around 0,6D for MSE with the A09 model (Plusoptix Vision Screener: the accuracy and repeatability of refractive measurements using a new autorefractor) this and other studies are not focused on anisometropia, for which IOD MSE errors could be minimized. Another study with a different plus optix model, reports a sensitivity of 100% for anisometropia (A comparison of plusoptiX A12 measurements with cycloplegic refraction). We included this study in the introduction.

Data Analysis

Please indicate how the reader can interpret Thibos’ notation in regards to the J0 and J45.
Say that the Cylinder component needs to be in negative form

R: This information has been added

Anisometropia Classification

I suggest writing the formulas used for calculating the SA, MA, and sMA.

R: The formulas were added

Statistical Analysis

Results

Sample characterization – 1^st paragraph move it to the methods section.

R: Paragraph moved

Refractive State
- Please provide a table or figure (Box plot) with the refractive error information, where is possible to see the mean, standard deviation, and range
- Figure 1 has limited information, I suggest including the percentages in the table mentioned above

R: A new table (table 4) containing this data was added to this section

Anisometropia
- Please, use written numbers when placing them at the beginning of a sentence. (e.g Forty-six not 46)
- Provide information about the level of anisometropia per type. Describe the mean, standard deviation, and range
- Suggest creating a figure (bar plot with the percentages of anisometropia, total, young age group and older age group)

R: Sentence rewritten
Mean, standard deviation, and range of anisometropia per type was added in table 4. An extra figure would duplicate the information.
Information about the age group is already included in table 5, distributed by the study cycle which indirectly represents age groups. An extra figure would duplicate the information.

Discussion

The authors found a statistically significant association between the frequency of myopic anisometropia and age/ scholarly. Could the authors extend the discussion on the etiology of myopic anisometropia, which probably implies an asymmetric eye growth? Discussing this point could help the authors to suggest actions/mechanisms to prevent anisometropia.

R: This is an excellent suggestion for future research. We can hypothesise that an excess of near-work activities, associated with incorrect posture, can lead to asymmetric eye growth. However, those factors were not controlled in the present study.

Discuss the consequences of hyperopic anisometropia, use the values (mean and standard deviation) for arguing about the number of subjects at risk of developing amblyopia.

R: Only 2 uncorrected anisometropes were hyperopic, and since no BCVA data was collected, we feel that there are no sufficient data to support this kind of analysis. However, we agree that it is an excellent suggestion for future work.

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Competing Interests

No competing interests.

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Reviewer Report

40 Views

12 Nov 2021 | for Version 1

40 Views Cite this report Responses(1)

Approved With Reservations

The study reports on the prevalence of anisometropia in a sample of Portuguese children and adolescents. The wording needs major revision. I have several comments as shown below.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.
Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.
There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

Results

The first paragraph should be moved to the methods section.
Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).
At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).
Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.
Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p value.
Table 3 – delete the X2 value and only present p value. Non-significant p values may be presented with only 2 decimal places.
For risk factor analysis the multivariate adjusted analysis should be additionally shown.
Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

Discussion

Please, delete the 1^st sentence.
The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.
Another limitation of the study that was not referred is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.
Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Refractive errors and strabismus

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Responses (1)

Author Response

08 Dec 2021

Amelia Nunes, UBIMedical, Universidade da Beira Interior, Covilhã, Portugal

We would like to thank the reviewer for her valuable time and comments on our article; this will be very useful for us in future research and has allowed us to improve this document. We have made the required corrections.

Title

I suggest replacing the word “frequency” by “prevalence”. This suggestion also applies throughout all sections of the manuscript.

R: The title was replaced

Abstract

Methods - Please replace “cycloplegic” by "cycloplegia”.

R: The word was replaced

Results - Please revise the wording of the following sentence “to state that the occurrence…”; The last sentence of the results it’s not clear and should be revised.

R: Sentence revised to “No statistical differences were found between genders or between areas of residence regarding the rate of anisometropia”;
Last sentence revised to “Regarding spherical equivalent anisometropia, there is a pattern of variation that increases with the cycle of studies (��²₍₃₎= 10.918; p = 0.012), with myopic anisometropia being the main contributor to this variation.”

Introduction

The first sentence is too long, and the wording needs to be revised. I suggest splitting it into two sentences. I have a similar comment for the third paragraph of the introduction section.

R: The first sentence was split and wording revised to:” Anisometropia is an ocular disorder characterized by an interocular difference (IOD) in refractive error. It represents a specific refractive condition where the two eyes of an individual, with presumably similar sociodemographic, environmental and genetic influences, can have asymmetric eye growth.”
The third paragraph split and wording revised to:” Although it is not clear what is the ideal age to perform the correction, in order to guarantee an ideal visual development and maturation, the early correction of anisometropia is important.¹¹ This prevents the development of other changes such as aniseikonia, amblyopia and strabismus^3,12,13 and even in small degrees (<1D) facilitates emmetropization.¹¹ It also improves quality of life, reducing or eliminating symptoms of visual discomfort.”

There is no mention to previous studies on anisometropia prevalence. Also, there is the need to show more detailed results on the studies reporting risk factors and its association with anisometropia (e.g., sample size, age, p values, etc.).

R: These data were introduced in a new table, and the reference numbering was changed accordingly.

Methods

The methods section is incomplete. The methods section of a research paper provides the information by which a study's validity is judged. Therefore, it requires a clear and precise description of how an experiment was done, and the rationale for why specific experimental procedures were chosen. For example, more information is necessary on the sampling method and authors should describe their study design.

R: The method section was completed including the following text “Data from the Portuguese Census 2011, shows a population of 319284 from 0 to 14 years old in the central region. For a confidence level of 95% and a 5% margin of error, taking into account that the prevalence of the studied condition is unknown, it was fixed at 50% to obtain a large enough sample size. The result was a minimum of 384 subjects. The data collection took place in 5 schools of the central region of Portugal, including all students that were authorized to participate by their legal guardians.”

Results

The first paragraph should be moved to the methods section.

R: The paragraph was moved

Table 2 – Replace “statistical test” by p value only (follow the same recommendation in the text results). Also, include a note referring to which comparisons are being made (for example, is it the distribution of children by cycles or the age by cycles?).

R: Done. This table was moved to the methods section, and the statistical analysis was deleted since it did not provide significant information.

At the time you are writing your article, you have already completed your study, so you should use past tense in your methodology and results section to record what you did and found (for example, “this difference was statistically significant”).

R: Text rewritten to past tense.

Refractive state and anisometropia sections need to be re-written, as it is confusing to present two percentages at the same time. Perhaps the authors can consider showing separate sentences for those results.

R: Both sections were rewritten to avoid double percentages.

Influence of sociodemographic variables: the first sentence of this section should be moved to the statistical analysis; Delete “therefore this parameter is not in the table” and replace by the p-value.

R: The sentence was moved to the methods section. “Therefore..” was removed and the p-value information was added to the table.

Table 3 – delete the X2 value and only present p-value. Non-significant p values may be presented with only 2 decimal places.

R: X2 values deleted and p values with 2 decimal places

For risk factor analysis the multivariate adjusted analysis should be additionally shown.

R: The multivariate analysis was added to the table.

Figure 2. The colour of the legend is not clear, and it is difficult to distinguish the categories presented in the graph. The y axis wording needs revision.

R: Legend colour changed. Y-axis caption revised.

Discussion

Please, delete the 1^st sentence.

R: Sentence deleted

The differences between prevalence of anisometropia in Asia and Europe need a more careful explanation. Environmental factors play a major role in the development of refractive errors, especially myopia.

R: An extra sentence was added to explain to acknowledge the contribution of environmental factors “Some studies show that lifestyle parameters, such as reading and writing habits and time spent indoors, contribute to the prevalence of anisometropia variation. ^7,8,10,11”

Another limitation of the study that was not referred to is that factors such as reading habits or outdoor time were not collected and those may be risk factors for the development of refractive errors.

R: We recognise the relevance of these factors, and they will be included in future studies. Accordingly to your suggestions, the following sentence was added to the end of the text “For future studies, data regarding reading habits and time spent outdoors will be collected, since these can be risk factors for the development of refractive errors.”

Is this the first study in Portugal? Are your results comparable with other studies in Portugal?

R: This is not the first study in Portugal, however in indexed research papers we couldn’t find any comparable studies for Portugal. We found an indexed research paper by Lança, Serra, and Prista in Portuguese children, which indirectly refers to the number of uncorrected anisometropic children, but the methodology is very different from ours, including the anisometropia classification criterium. However, the percentage of uncorrected anisometropia is similar. We considered this fact relevant and it was included in the discussion.

Conclusions

Please revise the wording on the sentence that includes the following: “we are of the opinion”.

R: The sentence was revised and divided to: “Taking into account the high frequency of anisometropia found in 3^rd cycle students, in our opinion the implementation of visual screening programs at this age is essential for the timely detection and correction of possible eye problems. This course of action will lead to better development, learning, and school outcomes at these ages.”

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Competing Interests

No competing interests.

Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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Frequency of anisometropia in children and adolescents

Abstract

Keywords

Introduction

Methods

Data analysis

(1)

(2)

(3)

Refractive state classification

Table 1. Classification criteria for refractive state [17] 16.

Anisometropia classification

Statistical analysis

Ethics approval

Consent to participate

Results

Sample characterization

Table 2. Sample characteristics.

Refractive state

Figure 1. Refractive error distribution.

Anisometropia

Influence of sociodemographic variables

Table 3. Relationship of gender, area of residence and study cycle, in anisometropia.

Figure 2. Relative frequency of the variation of the various types of anisometropia, with the school cycle.

Discussion

Conclusions

Data availability

Underlying data

Acknowledgments

References

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