Novel method of measuring not corrected visual acuity with a smartphone

Abstract

Purpose : Visual Acuity (VA) is usually measured at a distance of 3-6m (10-20 feet) because it is affected not only by neural (i.e. amblyopia) but mostly by optical (i.e. myopia) factors. VA can be measured using a smartphone, however the size of the device’s screen can limit the maximum measurement distance to less than 2 m for low VA’s due to the target not fitting on the screen. We study a new method to measure VA interactively with smartphones, at a distance comfortable for the patient, avoiding the optical limitations due to its proximity to the patient.

Methods : Standard clinical measurements of not corrected VA were performed in both eyes of 24 subjects of different ages (35 ± 16 years), using an ETDRS optotype placed 6 m away. These measurements were compared with those obtained with a mobile application (app) used on four different devices. The test used for the measurements with the electronic device consisted of a Landolt C optotype following a four-choice algorithm. Target’s size is rescaled automatically by a continuous measurement of the distance device-user by means of the front camera of the device. A blue letter on a black background was used as target so that the measurement made at a distance of 1 or 1.5 m was equivalent to that of a black and white test located at a distance of 3 m or infinity, respectively, due to the longitudinal chromatic aberration of the human eye.

Results : The mean difference between clinical and experimental values of VA for both eyes were 0.013 ± 0.155 and 0.009 ± 0.174 logMAR for the test located at 1m and 1.5 m, respectively. The statistical analysis showed no significant differences between the clinical values and those obtained by the device (p-value 0.443 and 0.461 for measurements at 1 and 1.5 m, respectively). Statistical analysis performed for each eye separately yielded similar results.

Conclusions : The results show that it is possible to measure VA with this novel method, and obtain results on par with the clinical standard (mean difference less than one letter on a line). The method can be used to screen for anomalies limiting patients’ VA so that they can be referred to an eye care professional, as well as for a remote follow-up of the evolution of a treatment such as amblyopia.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.