Factors associated with the presence of cataracts in the Peruvian population older than 50 years: a cross-sectional study [version 1; peer review: awaiting peer review]

Background: Cataracts are a public health problem, especially in low-and middle-income countries, where the greatest limitations of health care systems are observed, making access to treatment difficult. This study aimed to determine the factors associated with the presence of cataracts in adults over 50 years of age in Peru. Methods: A cross-sectional analytical observational study was performed of data from the 2019 Demographic and Family Health Survey (ENDES – acronym in Spanish). The dependent variable was the self-reported diagnosis of cataracts (yes or no). Crude and adjusted prevalence ratios (aPR) were calculated using a generalized linear model of the Poisson family with a log link function to estimate factors associated with self-reported cataract diagnosis. Results: We analyzed the data of 8775 Peruvian adults older than 50 years; 1322 (16.68%) self-reported a diagnosis of cataract. A higher prevalence of having cataracts was associated with being aged 60-69 years (aPR: 1.40; native ethnicity, having had a visual acuity evaluation in the last 12 months and having diabetes were associated with a higher prevalence of cataracts. These factors should be considered when implementing strategies for health education, promotion and prevention to ensure access to early ophthalmologic care.


Introduction
Cataracts continue to be a global public health problem because they are one of the most prevalent eye diseases. 1,2 This disease has a multifactorial cause that generates the opacity of the crystalline lens of the eye, subsequently causing progressive and painless loss of vision. 3 Globally, by 2015, cataracts were the leading cause of blindness (about 12.6 million people; 35.0% of all cases of blindness) and the second leading cause of moderate or severe visual impairment in all age and ethnic groups (about 52.6 million people; 24.3% of all causes). 4 In 2020, it was estimated that at least 13.4 million cases of blindness were due to cataracts, and about 127.7 million cases of low vision were related to this disease, 4 generating more than 6 million disability-adjusted life years in 2019. 5 Due to this increase in the prevalence and burden of cataract disease, the need for timely diagnosis is essential to provide accessibility to surgical treatment of this disease. 1 Biomedical literature has described an increase in the number of cases of cataracts. This increase translates into a greater burden for health care systems, since untimely diagnosis and treatment can have immediate and long-term consequences such as the development of ocular complications, 6 causing increased dependence on others due to visual impairment, 5 increased risk of fractures, 7 decreased quality of life, 8 increased risk of mortality, 9,10 and economic losses for the individual, family and society. 11 Despite vision impairment and blindness being most common in people over the age of 50 12 and cataracts being a disease that can be treated by surgery. 13 The prevalence of avoidable visual impairment and cataracts in the adult population aged 50 years or older has not improved, in fact the number of cases has continued to rise since 2010. 2 Similarly, lack of population health awareness and literacy, shortage of trained eye health personnel in all urban and rural areas, limited accessibility to an ophthalmologist, the high cost of access to corrective surgery, and insufficient outcomes to correct the visual defect with surgery remain an obstacle for reducing blindness by cataracts, particularly in low-income countries. 3,14 In low-and middle-income countries, it is necessary to know the factors associated with an increased risk of cataracts in order to design screening strategies and public health intervention measures. Although different factors have been associated with the development of cataracts, including marital status, age, educational level, smoking, diabetes mellitus, as well as exposure to sunlight, and body mass index (BMI), most of these factors have been evaluated in specific populations with ophthalmologic problems. [15][16][17] In the countries that make up the Andean region of Latin America (Bolivia, Ecuador, and Peru), cataracts account for 27.5% of cases of blindness and 44.6% of cases of moderate to severe visual impairment. 4 However, there is little scientific research in these countries on the factors related to cataract diagnosis in the general population.
In Peru, cataracts account for 58.0%, 59.3%, and 21.8% of the cases of blindness, severe visual impairment and moderate visual impairment, respectively. 18 In addition, about one in three patients diagnosed with a cataract do not undergo surgical treatment. 18 Although cataracts are the main cause of blindness and severe visual impairment in Peru and prevalence significantly increases with age (being most common in people over the age of 50 years), 19 no previous study has evaluated the magnitude and factors associated with cataract diagnosis in this population. Therefore, the objective of this study was to determine the factors associated with cataracts among adults over 50 years of age in Peru.

Study design and population
A cross-sectional analytical observational study was conducted using data from the Demographic and Family Health Survey (ENDESacronym in Spanish) 2019. This survey is prepared by the National Institute of Statistics and Informatics of Peru (INEIacronym in Spanish) and consists of three questionnaires: household and its members, individual health of women, and health (persons over 15 years of age). The ENDES used a two-stage, probabilistic, balanced, stratified, and independent sampling. The unit of analysis is the usual residents of the dwellings selected through complex sampling. The ENDES allows obtaining representative results at the national level, by urban and rural areas, in each of the country's 24 departments and the constitutional province of Callao, as well as for the natural regions of Peru (Coast, Highlands, and Jungle). Geographically, Peru is divided into three natural regions: the Coast, which borders the Pacific Ocean, includes Lima (the capital of Peru) and is one of the regions with the highest population density and access to health services in the country; the Highlands, which includes the areas with the highest altitude in the country and the lowest wealth index; and the Jungle, the region with the greatest biodiversity, the largest geographic territory and the greatest barriers to access to health services. Further details of the methodology used in the ENDES are reported in the technical sheet of the survey.
In this study, the ENDES 2019 Health Questionnaire data were used, which collected information from 36,760 households. From these households, only participants with complete information on self-reported cataract diagnosis and who were 50 years of age or older were included. Finally, a total of 8775 individuals were included for analysis.

Dependent variable
Cataract diagnosis, defined by the respondent's self-report, indicated that the respondent had previously been diagnosed with cataracts by an eye doctor (ENDES question: Have you ever been diagnosed with cataracts by an eye doctor?). For the analysis, two categories were considered for this variable: "Yes", when the respondent gave a positive answer to the survey question, and "No", when the answer was negative.

Statistical analysis
The analyses were performed with the statistical program R (R Project for statistical computing, RRID:SCR_001905). The loading of the databases in.sav. format and their union were performed using the haven function, tidyverse (RRID: SCR_019186), and survey using different relational and hierarchical structures depending on the database needed to perform our analysis. All analyses considered the weighting and sample specifications of the ENDES 2019 using the svydesign function. A value of p<0.05 was considered statistically significant.
The characteristics of the participants included were described using absolute frequencies and weighted proportions. Then, to compare the proportions of the dependent variable (self-reported cataract diagnosis) among the categories of the independent variables, the chi-square test with Rao-Scott correction was used. Finally, crude (PR) and adjusted (aPR) prevalence ratios and their respective 95% confidence intervals (95% CI) were reported using generalized linear models of the Poisson family with logarithmic link function to estimate the factors associated with self-reported cataract diagnosis. In the fitted model, all independent variables with a p<0.05 in the crude model were included. To evaluate the collinearity of the independent variables included in the adjusted model, the variance inflation factor was used, where a value >10 determined multicollinearity among the variables; however, all values obtained were less than 10.

Ethical considerations
Approval by an ethics committee was not requested because this is an analysis of secondary data that are in the public domain and do not allow the identification of the participants. The ENDES databases are freely accessible and can be freely obtained on the web platform of the INEI. This institution requested the consent of participants to obtain the information required in the survey. All participant data were anonymized prior to access.

Results
The data of 8775 Peruvian adults over 50 years of age were analyzed. Of these, 52.29% were women, 43.91% were in the 50-59 age group, 24.50% were of native ethnicity, 45.22% had no or only primary education, 78.62% had health insurance, 28.85% of the respondents had not had a visual acuity examination in the last 12 months, 6.18% had high blood pressure, 9.22% had diabetes, and 28.23% had obesity. Regarding wealth quintiles, most households were in richer (20.67%) and richest quintile (24.00%). In relation to the area of residence, 21.38% lived in rural areas. In terms of geographic area, most of the participants resided in the Coastal region (63.26%) and at an altitude of 0 to 499 meters (65.42%) ( Table 1).

Discussion
This study sought to estimate the factors associated with cataract diagnosis in Peruvian adults over 50 years of age.
The factors associated with a higher prevalence of presenting cataracts were older age groups, higher education level, belonging to the highest wealth quintiles, self-identification of native ethnicity, presenting diabetes mellitus as a comorbidity, and having had a visual acuity evaluation in the last 12 months. Conversely, having a higher level of education was associated with a lower prevalence of having cataracts.   27 and severe visual impairment (59.3%) in Latin America. 18 The presence of cataracts can be related to multiple long-term negative outcomes, including blindness and visual impairment, especially in the older adult population, [28][29][30] and therefore, we suggest promoting national strategies to ensure the screening and diagnosis of this health problem, as well as access to an ophthalmologic evaluation in primary care facilities. In this regard, the American Academy of Ophthalmology recommends that adults should undergo a complete ophthalmologic evaluation at the age of 40 since the first signs of diseases or changes in vision, including cataracts, begin to appear at this age. 31 In addition, it is important to increase cataract surgery coverage since Peru has one of the lowest rates in Latin America (20 to 24%). 27,32 A higher probability of cataracts was associated with being an older adult (60 years and older). In general, increasing age is described as the main factor for the presence of any type of cataract. 22 The results of the present study are consistent with previous population-based studies in Australia and Asia, which reported that the prevalence of cataracts increases with age, from 3.9% between the ages of 55 and 64 years to 92.6% after the age of 80 years. 16,17 The lens opacity that occurs in age-related cataracts may be directly caused by oxidative stress that increases with aging, which causes normal lens proteins to begin to disintegrate, resulting in opacity. 1,33 Therefore, older adults are more susceptible to cataracts, thereby requiring greater efforts in the prevention of this disease.
A higher education level was associated with a lower prevalence of cataracts. The difference in the prevalence of cataracts with respect to the educational level found in this study coincides with what has previously been reported in the literature. 34,35 It should be considered that a higher level of schooling is related to a higher level of knowledge of this disease and, therefore, to a greater understanding of prevention and treatment. 14 In this regard, it has been reported that a low educational level could be related to a higher rate of rejection of surgical cataract treatment. 18 Therefore, increasing access to information about this disease, with emphasis on lower educational level groups, would help to prevent its progression, as well as to detect and treat the disease early, giving this approach the chance of being a useful strategy for the control of this disease.
Concerning the wealth quintile, we found that belonging to the poorest quintile was associated with a lower prevalence of cataracts. This finding differs from other literature since it has been suggested that the poorest socioeconomic levels have a higher frequency of cataracts 36,37 and that poverty represents a barrier to early diagnosis of cataracts. 38 This finding could be explained by the fact that the diagnosis of cataracts was obtained by self-reporting. It is possible that people with a higher socioeconomic level have greater access to medical specialists and that in the event of a possible decrease in visual acuity, they can go to an ophthalmologist early for evaluation of a possible diagnosis of cataracts. On the other hand, the respondents who belonged to the poorest quintiles possibly face difficulties in going to a medical specialist for a timely diagnosis of cataracts, even though, according to scientific evidence, these groups have a higher incidence and prevalence of cataracts. Therefore, the lack of access to diagnosis in this group of people could be related to the lower prevalence of cataracts observed in comparison to the groups in the higher welfare quintile. Taking this into account, the promotion of greater vision care and ophthalmologic evaluations for early detection of the disease in the less socioeconomically favored groups should be considered.
Self-identification as native ethnicity was found to be associated with a higher prevalence of cataracts. In this regard, a previous study in a geographically isolated Guatemalan native population reported a high prevalence of cataracts (54.8%). 39 It has been reported that the native population (including Quechua, Aimara, and native or indigenous ethnic groups of the Amazon), which is part of ethnic minorities, tends to experience limitations in access to health services, including ophthalmologic care, with a lack of effective strategies to achieve better communication and distribution of medical care among the native population. 39 In Peru, there are barriers such as the shortage of ophthalmologists, surgeons, and equipment for the definitive treatment of cataracts, thereby generating great inequity mainly affecting socially and economically disadvantaged populations such as the native population. 40 Therefore, it is necessary to improve the epidemiological surveillance of cataracts to identify vulnerable populations in need of intervention and promote cataract surgery campaigns in populations with a higher prevalence of the disease.
Having diabetes mellitus was associated with a higher prevalence of cataracts. This risk factor has been identified in several population-based studies suggesting a causal association between diabetes and nuclear, cortical, posterior subcapsular, and age-related cataracts. 23,35,41,42 This relationship is explained by changes in the cortical and nuclear lenses resulting from increased glycosylation of lens proteins. 35 Since diabetes is a major public health problem in Peru affecting between 5.1 and 7.0% of the adult population, 43,44 reflecting the aging and unhealthy lifestyles of the population, primary prevention programs against diabetes should be strengthened and implemented in order to reduce the prevalence of eye problems such as cataracts, glaucoma, or diabetic retinopathy that may result in an increased risk of severe ocular disability or blindness.
Finally, among the associated factors, having had a visual acuity evaluation within the last 12 months was also associated with a higher prevalence of cataracts. This finding is likely because people who visited the ophthalmologist within the previous 12 months may have had a previous diagnosis of cataracts or problems related to visual acuity and therefore had control or appointment for evaluation by the ophthalmologist with possible confirmation of a diagnosis of a cataract. 26 In our study, about seven out of ten adults aged 50 years and older had never had an ophthalmologic evaluation, which implies and highlights a lack of coverage in the detection of ophthalmologic problems (including cataracts) within the Peruvian health system. Therefore, it is necessary to provide a free and timely ophthalmologic evaluation from the first level of care in order to intervene early in a greater number of patients.
There are some limitations in the present study that should be considered. First, the use of a secondary database implies the unavailability of other variables of interest in relation to the outcome studied, including environmental and respondent characteristics, which could not be considered in the analyses. Second, the possible introduction of bias regarding the condition of having or not having cataracts should be kept in mind because the responses to questionnaire questions were self-reported. Third, due to the absence of temporality according to the study design employed, it is not possible to study causality between the factors included in the analysis and the presence of cataracts. Despite these limitations, we consider that the findings of this study can provide a macro view of the factors associated with cataracts in the Peruvian population over 50 years of age. Likewise, the use of the ENDES, a nationally representative survey conducted annually using methodological quality control processes, allows the adequate study of the problem of interest.
In Peru, one out of six adults over 50 years of age have been diagnosed with cataracts. We identified that those older than 60 years, of native ethnicity, higher wealth quintiles, having diabetes mellitus, and having had a visual acuity evaluation in the last 12 months were associated with a higher prevalence of cataracts, while having a higher educational level was associated with a lower prevalence of cataracts. These factors should be used to improve and implement strategies or programs for health education, promotion, and prevention that ensure access to early ophthalmologic care, prioritizing the oldest age groups, native ethnic groups, and the poorest population, in order to detect and treat this disease early, leading to lower costs for both individuals and the health system.

Source data
The ENDES 2019 dataset used in this study is freely available at Microdatos INEI: http://iinei.inei.gob.pe/microdatos/. A login or registration to access the database is not required.