Use of best and final visual acuity outcomes in ophthalmological research

Objective: To evaluate how often visual acuity outcomes are reported in the ophthalmological literature as best or final outcomes, despite potential bias with this type of analysis, as compared with interval outcomes, when a specific condition may continue to cause gain or loss of visual acuity beyond the time that the best or final outcome is determined. Methods: Each article published in the 3 most frequently cited comprehensive clinical ophthalmological journals in the United States from January through December 2000 was reviewed. Clinical studies were identified in which visual acuity was used as an outcome measure. Visual acuity outcomes were examined throughout the articles and classified as follows: best visual acuity, defined as an outcome at any time during follow-up; final visual acuity, defined as an outcome at last follow-up; and interval visual acuity, defined as an outcome at specified follow-up times. A few factors that might be associated with the different types of outcome were evaluated. Reproducibility of the categorization between 2 ophthalmologists evaluating the articles was determined by using the kappa statistic. Results: A total of 527 clinical studies met the criteria. Among these, authors of 195 reported visual acuity as an outcome measure. Authors of 1 article (0.5%) reported only best visual acuity, authors of 6 (3%) reported both best and final visual acuity, authors of 113 (58%) reported only final visual acuity, and authors of 73 (37%) reported interval visual acuity outcomes. Reproducibility of these categorizations between 2 ophthalmologists was considered excellent, as compared with chance alone (kappa = 0.84). Authors of only 2 of the 120 articles that used either best or final visual acuity outcomes discussed the limitations or potential bias of reporting outcomes in this way. Randomized trials and other prospective study designs more often were associated with interval outcomes than were non-randomized and retrospective studies. Conclusions: Despite potential bias with use of best or final visual acuity outcomes, these end points alone were used in most studies published during 2000 in the 3 most commonly cited journals. Authors of clinical studies should consider avoiding use of best or final visual acuity outcomes whenever possible to minimize possible data misinterpretation. If best or final outcomes are used, authors should consider discussing the limitations of these methods and their potential effect on the interpretation of results.