Results from smartphone-based Snellen charts, which are eye charts used to measure visual acuity, are not consistent with results from standard Snellen visual acuity chart tests, according to a study conducted by researchers from the University of Melbourne. The study was published in Eye, which is the official journal of the The Royal College of Ophthalmologists.

The Snellen test requires the patient to read numbers and letters line by line from a physical chart while standing a specific distance away. The numbers and letters decrease in font size the lower the patient reads.

"Smartphone-based Snellen visual acuity charts [have] become popularized; however, their accuracy has not been established," researchers wrote in the abstract. "This study aimed to evaluate the equivalence of a smartphone-based visual acuity chart with a standard 6-m Snellen visual acuity (6SVA) chart."

Researchers first reviewed Snellen chart apps that were available for the iPhone and found 11, though the accuracy of these apps varied significantly, from 4 percent to 40 percent accurate. They then conducted a study with 88 patients from general medical and surgical wards in an Australian hospital to compare a patient's results from a conventional test and the most accurate app from the review. Researchers used the iPhone 4 for this test.

This comparison showed that the Snellen visual acuity app could not predict a patient's standard Snellen visual acuity within one line. Researchers added that further validation is required to assess the acuity in patients with severe vision impairment.

While there are no FDA-cleared Snellen test apps, at least one other vision test application has pursued and secured FDA clearances in recent years.

A few months ago, Vital Art and Science, developers of myVisionTrack, a vision test service for patients with age-related macular degeneration or diabetic eye disease, received a second FDA clearance for their platform, which includes an app and a provider dashboard. The app addresses age-related macular degeneration, which is one of the leading causes of blindness. It allows patients to track subtle changes in their vision and automatically alerts their physician, which enables doctors to launch an intervention early, before the patient loses more of their vision.