Randomized controlled trials in ophthalmology: a bibliometric study

Introduction

Since the conception of the term “evidence-based medicine” in clinical practice in 1992¹, where well-conducted randomized controlled trials (RCTs) are situated at the top of hierarchy of evidence, there has been an emphasis on accepting high quality evidence in terms of RCTs in clinical practice. Moreover, previous reports showed that RCTs have generally higher methodological rigor than observational studies². However, despite the rapid growth in ophthalmology literature in the recent years, this growth has not been paralleled by a growth in the quality of evidence³. This is evident by the number of Cochrane reviews that don’t include any RCTs (i.e. empty review), which were estimated to be half of the total reviews on Cochrane Eyes and Vision in 2013⁴. In this study, we aim to assess the status of RCTs in ophthalmology, and will focus on publishing trends for RCTs in ophthalmology in the recent years with regards to different ophthalmology topics.

Methods

Results

Ophthalmology RCTs

A total of 540,427 publications in the field of ophthalmology were identified, of which only 11,634 (2.15%) of them were RCTs. There was a total of 482,791 RCT identified in all disciplines, of which only 2.4% are in the field of ophthalmology. Of these trials, 124 were phase 1 trials, 270 were phase 2 trials, 380 were phase 3 trials, and 42 phase 4 trials; all others did not have phases. Number of RCTs peaked in 2015 with a total of 583 trials. Figure 1 shows the trend in number of RCTs in the field of ophthalmology.

Figure 1. Number of randomized controlled trials published per year in the field of ophthalmology from 1961 to May 2019.

RCTs in each ophthalmology topic

‘Retinal diseases’ is the topic with the highest number of RCTs, with a total of 2915 trials, followed by ‘glaucoma’, with 2118 trials, and ‘conjunctival diseases’, with 1230 trials. Figure 2 details the number of trials for each topic.

Figure 2. The number of randomized controlled trials (RCTs) for each topic in ophthalmology.

Discussion

In the current study, we observed a peak in the annual number of RCTs on 2015, after which a steady decrease observed till 2018. Retinal diseases is the topic with the highest number of RCTs, followed by glaucoma and conjunctival diseases. The trial with highest citation was on retinal diseases and was published in The New England Journal of Medicine, where also other top cited trials were published in general non-ophthalmology journals. The total RCTs published in top 100 ophthalmology journals was only 2090 (17.96%).

In general, there has been an increase in the number of RCTs in ophthalmology since the late 1990s. In a study assessing the frequency of prospective studies published in the American Journal of Ophthalmology and British Journal of Ophthalmology, they found an increase from 1% to 12% during the years 1980 to 1999⁷. We observed a low number of RCTs among the ophthalmology literature, a percentage that didn’t exceed 2.5% of the overall ophthalmology literature. In a previous study assessing the frequency of RCTs published in the major four ophthalmology journals, they found that only around 3.5% of their annual publications are RCTS⁸. Moreover, we found that only around 18% of all ophthalmology RCTs are published in the top 10 ophthalmology journals, with the most RCTs (5.53%) published in Ophthalmology. In a study that reviewed risk of bias in RCTs published in major ophthalmology journals found that a risk of bias was observed in 29.4% of published RCTs⁹. In another study that assessed fragility of RCT’s that included the comparison between two groups found a high proportion of fragile results in ophthalmology RCTs¹⁰. In a study that assessed types of articles published in core pediatric journals, they found that only 0.3% were RCTs¹¹, which supports our findings that a large proportion of RCTs were published in high-impact general medical journals.

One of the main limitations in this study is that it didn’t assess the quality of RCTs, so we included RCTs from our PubMed search regardless of their quality. Recent studies have stated that ophthalmology literature is of questionable methodological robustness, where RCTs become the center of the scope when methodological robustness is assessed, as they are the source of the highest level of evidence^10,21. Future studies should focus on assessing quality of RCTs rather than the quantity (which was the scope of this study), where the Cochrane Eyes and Vision library criteria for RCT robustness can be utilized²².

Data availability