Work

Magnitude of Visual Acuity Change with ETDRS versus Snellen Testing in Clinical Trials

Year: 2023

Type: article

Abstract: Purpose To compare visual acuity (VA) changes using standardized Early Treatment Diabetic Retinopathy Study (ETDRS) best corrected visual acuity (BCVA) and non-standardized Snellen VA among subjects enrolled in clinical trials Design Retrospective study Participants Patients enrolled in prospective clinical trials at three urban retina practices. Methods Best available Snellen VA at the clinic visit before study entry and after exit were compared with the ETDRS BCVA at trial entry and exit. The correlation and discrepancies between Snellen VA and ETDRS methods as well as the VA changes from trial entry to exit were evaluated. Main outcomes measures The discrepancy between VA change from trial entry to exit using Snellen VA vs. ETDRS BCVA methods. Results A total of 273 eyes were included. The mean (SD) Snellen VA was 58.1 (20) ETDRS-equivalent letters (Snellen 20/69) at the clinic visit before trial entry and 61.6 (21) ETDRS-equivalent letters (Snellen 20/59) at the visit after trial exit. The mean (SD) ETDRS BCVA was 65.5 (16) letters (Snellen 20/49) at trial entry and 70.5 (17) letters (Snellen 20/39) at trial exit. The mean VA change from trial entry to exit was not significantly different for ETDRS (5 letters of vision gain) compared to Snellen (3.6 letters of vision gain) methods (p=0.061). Eyes with baseline Snellen VA 20/50 or worse gained significantly more letters using Snellen (9.3 ± 22.3 letters) compared to ETDRS (5.2 ± 18.7 letters, p=0.012). Among eyes with baseline Snellen VA ≥ 20/50, VA gain was significantly greater with the ETDRS method (4.9 ± 12.3 letters) compared to Snellen (-1.5 ± 12.3 letters, p<0.001). Conclusion The mean VA change from clinical trial entry to exit was similar between the ETDRS and Snellen methods. However, among patients with worse baseline Snellen vision, the magnitude of VA change was greater with Snellen compared to ETDRS, while among those with better baseline vision, this magnitude was greater with the ETDRS method. Understanding the proportion of the study population with varying VA levels may have implications for interpreting real-world VA outcomes compared to those reported in clinical trials.

Source: Ophthalmology Science

DOI: 10.1016/j.xops.2023.100372