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A Cochrane systematic review for corneal-disease treatments suggest that ~34% of studies are unreliable

A Cochrane comprehensive study has reported that one in 3 systematic reviews addressing interventions for corneal diseases are unreliable. As a result, the systematic review of the studies could not be used to inform clinical practice guidelines from the American Academy of Ophthalmology (AAO). In the study, 33 of 98 systematic reviews (34%) were classified as unreliable and the most persistent reasons for unreliability were that the systematic review did not have a comprehensive literature search, that there was a risk of bias, or that inappropriate methods for meta-analysis (either qualitative and/or quantitative) were applied. Regardless, on a positive side, 65 of the 98 systematic reviews (66%) were classified as reliable.  The systematic review shows that 42 of the 65 reliable systematic reviews (65%) addressed corneal diseases, and these studies are relevant to the 2018 American Academy of Ophthalmology “PPPs” – i.e. “Preferred Practice Patterns” – which the AAO are “designed to identify characteristics and components of quality eye care”.


Corneal disease is the 4th leading cause of blindness, numbering an estimated 5% of cases of blindness globally.   The systematic reviews were addressing interventions for 6 corneal diseases, including bacterial keratitis, blepharitis, conjunctivitis, corneal ectasia, corneal edema and opacification and dry eye syndrome. The 2016 cataract PPP and the 2017 refractive error PPP are also identified as recent examples and are available in systematic reviews.


In a discussion of the report it appears that over the last 10 years there has been a 3-fold increase in the number of systematic reviews on medical care health subjects in the literature. The increase of ophthalmic research is clearly shown in the growth of related systematic reviews: from 547 systematic reviews in 2007 to 3,777 systematic reviews in 2017. Aside from the concerns for not having comprehensive literature studies, risk of bias and methodologies, there was also a potential difficulty for conflict-of-interest issues. Authors have identified that 15 of 33 of the unreliable systematic reviews and about 24 of 65 the reliable systematic reviews “did not report funding sources”. In commenting in the discussion, the research paper stated that: “Within ophthalmology, there has been increasing recognition of the influence of author conflicts of interest, either in the form of financial relationships or intellectual beliefs. Conflicts of interest, financial or intellectual, can alter the interpretation of identified studies, potentially leading to bias”.