Visual acuity measured with a smartphone app is more accurate than Snellen testing by emergency department providers

To assess the accuracy of best-corrected visual acuity (BCVA) measured by non-ophthalmic emergency department (ED) staff with a standard Snellen chart versus an automated application (app) on a handheld smartphone (Paxos Checkup, San Francisco, CA, USA). The study included 128 subjects who presented to the Stanford Hospital ED for whom the ED requested an ophthalmology consultation. We conducted the study in two phases. During phase 1 of the study, ED staff tested patient BCVA using a standard Snellen test at 20 feet. During phase 2 of the study, ED staff tested patient near BCVA using the app. During both phases, ophthalmologists measured BCVA with a Rosenbaum near chart, which was treated as the gold standard. ED BCVA measurements were benchmarked prospectively against ophthalmologists' measurements and converted to logMAR. ED logMAR BCVA was 0.21 +/- 0.35 (approximately 2 Snellen lines difference +/- 3 Snellen lines) higher than that of ophthalmologists when ED staff used a Snellen chart (p = .0.00003). ED BCVA was 0.06 +/- A 0.40 (less than 1 Snellen line +/- 4 Snellen lines) higher when ED staff used the app (p = 0.246). Inter-observer difference was therefore smaller by more than 1 line (0.15 logMAR) with the app (p = 0.046). BCVA measured by non-ophthalmic ED staff with an app was more accurate than with a Snellen chart. Automated apps may provide a means to standardize and improve the efficiency of ED ophthalmologic care.