The eye phone study (EPS): reliability and accuracy of assessing Snellen visual acuity using smart-phone technology

Purpose:To evaluate the equivalence of a smartphone-based visual acuity chart with a standard 6 metre Snellen visual acuity chart. Methods: firstly a review of available Snellen chart applications on iPhone was performed to determine the most accurate application based on optotype size. A prospective comparative study was performed by measuring conventional 6 metre Snellen visual acuity (6SVA) and then iPhone visual acuity using the 'Snellen' application on an Apple iPhone 4 in a sample of 88 patients from general medical and surgical wards in a tertiary hospital. Single-letter scoring was employed for both charts by converting Snellen chart line acuity measurements to logMAR score. Paired sample t-test was used to compare the logMAR score of two charts. Results: there was no significant mean difference in logMAR visual acuity between the two charts (mean difference= 0.02 logMAR, 95% CI -0.017 to 0.057 logMAR, p=0.293). Overall, there was less than one line mean difference in acuity between the two charts. The largest mean difference in logMAR acuity was noted in the subgroup of patients with 6SVA worse than 6/18 (n = 5), who had an approximate difference of 2 Snellen visual acuity lines (0.276 logMAR). ConclusionThe 'Snellen' application on the iPhone 4 is comparable within one line accuracy to a 6 metre Snellen visual acuity chart for use at the bedside in a general hospital setting. Further validation is required for assessment of acuity in patients with severe vision impairment