Development and Validation of a Mobile Visual Acuity Examination App for Universal Use, Including Remote and Rural Regions

Abstract

Background: Visual refractive errors are projected to rise in the coming decades worldwide, especially in remote and rural regions. To combat this, smartphone visual acuity testing apps may allow for the early detection of refractive errors thanks to their low cost and wide availability. Hence, we developed the OcularCheck app as a free mobile vision screening tool for public health use. Objective: We sought to determine whether OcularCheck accurately measures distance visual acuity (DVA) in comparison to a standard Snellen chart (Space Saving Chart SSC-350). Methods and Results: In January 2021, we measured DVA in n=56 eyes using the OcularCheck app and a standard Snellen chart. To minimize bias, we used two separate examiners who were blinded to each other’s measurements. To assess the similarity of measurement methods, we performed a two-tailed, paired t-test and Bland-Altman analysis using the R-Project software. The t-test showed that differences in DVA between testing methods were not significant (P=0.698). Bland-Altman analysis showed that the mean difference between measurement methods was 0.01 LogMAR (95% CI -0.03 to 0.04), and the standard deviation of differences (0.139 LogMAR) was below the test-retest variability of the Snellen chart. The main limitation of the study was that we were not able to measure DVA with non-English optotypes. Conclusion: OcularCheck provides accurate DVA measurements, and it harbors the potential to expand the accessibility of DVA screening to resource-scarce regions.