Use of log-scaled crowded visual acuity charts in clinical studies regarding amblyopia

Log-scaled crowded charts using standardized testing protocol are essential for precise and reproducible visual acuity (VA) testing regarding amblyopia. Despite common acceptance of these standards, current VA testing clinical practice shows considerable diversity. The purpose of this retrospective literature review was to investigate the methodology of VA measurement and reporting in pediatric ophthalmology literature regarding amblyopia.

We searched PubMed for clinical trials regarding amblyopia, published from January 1994 to July 2016. Primary outcomes included VA measurement methodology, namely use of (a) log-scaled chart, (b) crowded chart, and (c) specified testing protocol. The study design, publication year, and the journal's impact factor were analyzed in relation to the primary outcomes.

Out of the 165 initial reports, 150 were included. VA was measured with a log-scaled chart in 65%, with a crowded chart in 57%, and with a specified protocol in 51% of studies. All three criteria were met in 43% of studies and in multivariable logistic model, they were associated with more recent publication year (odds ratio [OR] = 1.11, 95% confidence interval [95%CI] = 1.03-1.20) and were more likely to be present in higher impact factor journals (OR = 1.42, 95%CI = 1.17-1.72) or randomized controlled trials (OR = 3.09, 95%CI = 1.44-6.59).

In the last two decades, more than half of clinical trials addressing amblyopia have not followed the recommended methodology for optimal visual acuity assessment. Thus, their measurements may have been contaminated with noise, and their respective results and conclusions may include errors. Adhering to optimal, standardized methodology is key to progress in both clinical and research grounds.