Abstract
Abstract: :
Background: Visual acuity is a frequent outcome measure in clinical trials of eye diseases. The protocol developed for the Early Treatment for Diabetic Retinopathy Study (ETDRS) is considered as the gold standard for acuity testing in clinical trials. We developed a PC-based system for visual acuity measurement that utilizes a programmed handheld device running the PalmTM OS connected to a PC running a Linux operating system and 17-inch monitor. Stimuli are single high contrast black-and-white ETDRS letters framed with surround bars. At a test distance of 3 meters, letters can be displayed from 20/800 to 20/12. Purpose: To develop a valid, reliable, better standardized, and more efficient test of visual acuity that is feasible for use in clinical trials. Methods: At 3 research-based eye clinics, 151 subjects with eye disease and 48 normal subjects with acuities ranging from -0.24 logMAR to 1.56 logMAR were each tested twice in one eye using both the electronic acuity testing algorithm (E-ETDRS) and the standard ETDRS (S-ETDRS) protocol. Test-retest reliability was assessed for each method and the test results with the two methods were compared to each other. Results: The E-ETDRS retest acuity scores were within 0.1 logMAR of the initial scores in 90% and within 0.2 logMAR in 99% (r=0.98). The S-ETDRS retest acuity scores were within 0.1 logMAR of the initial scores in 86% and within 0.2 logMAR in 97% (r=0.98). Comparing the E-ETDRS and S-ETDRS scores, on the initial testing 75% of scores were within 0.1 logMAR and 94% were within 0.2 logMAR (r=0.96) and on the repeat testing the percentages were 83% and 96%, respectively (r=0.96). Conclusion: The E-ETDRS testing algorithm has high test-retest reliability and produces visual acuity scores similar to S-ETDRS scores. It may be feasibly implemented in clinical trials without loss of measurement precision and offers the potential to reduce bias through gains in standardization, measurement efficiency, and electronic data capture.
Keywords: 356 clinical (human) or epidemiologic studies: systems/equipment/techniques • 620 visual acuity • 359 clinical research methodology