Validation of a Portable Electronic Visual Acuity System

Background: The use of tablet devices and smartphones in medicine as assessment tools is becoming more widespread. These devices now run mobile applications or ‘‘apps’’ that have traditionally been the domain of desktop computers or more dedicated hardware. It is important that health professionals have confidence in the accuracy of measurements obtained from these new tools. The ‘‘EyeSnellen’’ app for the iPhone/iPad (running Apple Inc’s iOS operating system) allows users to measure visual acuity using a portable Snellen chart installed on a tablet device. Aims: To compare the visual acuity measurements obtained from EyeSnellen iPad app with a standard illuminated Snellen Chart. Methods: Participants were recruited from a tertiary level eye clinic in Western Australia. Visual acuity was measured using the Snellen light box chart and a visual acuity measurement was obtained using EyeSnellen app installed on an Apple iPad mini with the use of an Apple Iphone as a remote that was connected via Bluetooth. Results: 122 eyes were tested. Bland-Altman analysis revealed a mean difference of 0.001 logMAR units between the visual acuity measurements obtained from EyeSnellen app and those taken on the light box chart with 95% limits of agreement of 0.169 to 0.171. Conclusion: The Snellen Chart function on EyeSnellen app is equivalent to the traditional Snellen chart at measuring visual acuity at a test distance of 6 metres.