Outcome reporting bias in ophthalmology clinical trials between 2014 and 2023

Outcome-reporting bias (ORB), characterised by selective outcome reporting, may exaggerate intervention efficacy and safety, compromising clinical guidelines and patient care. This cross-sectional analysis investigated the prevalence and extent of ORB in seminal ophthalmic randomised controlled trials (RCTs).

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we searched Embase, MEDLINE and CENTRAL for ophthalmic RCTs published in the 10 highest-impact ophthalmic and general medical journals from 2014 to 2023. Outcomes were incompletely reported if they lacked sufficient data for meta-analysis and unreported if specified in protocols but absent from publications. Logistic regression evaluated associations between incomplete reporting and trial or journal characteristics. The association between outcome unfavourability (ie, failure to demonstrate superiority, non-inferiority or equivalence) and incomplete reporting was calculated as OR and synthesised into a meta-analysis. Discrepancies between prespecified and published outcomes were examined.

Of 9436 records, 260 RCTs met inclusion criteria. Among these, 167 (64.2%) and 124 (47.7%) trials had at least one incompletely reported outcome and unreported outcome, respectively. Unreported outcome was associated with lower 5-year impact factor (adjusted OR (aOR): 1.02, 95% CI 1.00 to 1.05, p=0.04, per 1.0 reduction), receiving only industry funding (OR: 1.98, 95% CI 1.02 to 3.85, p=0.04) or not declaring funding compared to non-industry funding (aOR: 3.52, 95% CI 1.22 to 10.18, p=0.02). Unfavourable outcomes were more likely to be incompletely reported than favourable ones (OR: 3.31, 95% CI 2.41 to 4.56, p<0.001). Outcome discrepancies occurred in 121 trials (46.5%).

ORB is prevalent in ophthalmic RCTs. Strengthening adherence to prespecified protocols and improving transparency in reporting are essential.