Assessment of a rapid method to determine approximate visual acuity in large surveys and other such settings

To evaluate the efficacy of an iPod application developed to rapidly measure approximate visual acuity (VA).

Prospective, cross-sectional study.

One hundred four subjects (104 eyes) with a wide range of VA underwent both Early Treatment Diabetic Retinopathy Study (ETDRS) VA testing and iPod application testing. The application presented 4 randomized ETDRS letters at the Snellen equivalent of 20/40 and 20/200 each. In separate analyses, sensitivity and specificity of the iPod test were determined using the ETDRS VA testing results as the gold standard and defining "failure" to see as identifying 1, 2, 3, or all 4 letters incorrectly out of 4 trials. The minimum number of iPod trials necessary to maintain high accuracy was determined by defining a "failure" as getting the first, first 2, first 3, or all trial letters incorrect. In 13 subjects, the time necessary to perform the testing was determined.

Forty-six subjects had an ETDRS Snellen equivalent VA ≥20/40; 45 had a VA <20/40 and ≥20/200; and 13 had a VA <20/200. The mean ± SD testing time for the 3 groups was 43 ± 13, 60 ± 15, and 72 ± 25 seconds, respectively. The highest sensitivity and specificity combination was observed when a "failure" was defined as getting all letters incorrect for both the 20/40 (sensitivity = 98.3%/specificity = 93.5%) and 20/200 (sensitivity/specificity both 92.3%) cutoffs.

An iPod application requiring about a 1-minute testing time provides an objective, portable, rapid, and low-cost method to determine approximate VA, allowing VA testing to be performed efficiently in large surveys and other settings where approximate VA should be measured.