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    Accuracy of Snellen Apps

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    Just how accurate are inexpensive smartphone apps at measuring Snellen VA? They might be close enough to use in a pinch—but only if the optotypes are the correct size, Australian ophthalmologists report.1 When they tested 88 hospitalized patients with a conventional eye chart and an iPhone 4 app (Snellen, Dr Bloggs Ltd.), the overall mean difference in logMAR VA between the 2 methods was 0.02 logMAR. But when patients were stratified by VA, the mean difference was greatest in the 6/18 or worse group: 0.276 logMAR, about 2 Snellen lines. The authors noted that the small size of this group limits the interpretation of the data.

    “For clinicians seeing patients in hospital, a smartphone visual acuity chart is a reasonable tool to assess visual acuity, if you don’t have access to anything else,” said coauthor Chandrashan Perera, MBBS, an ophthalmology resident at Fremantle Hospital, in Western Australia. “The main thing is to realize that there is a lot of variability among these apps.”

    The researchers downloaded 11 free or 99-cent iTunes apps for the study, but only 3, including the Snellen app discussed above, had onscreen optotypes within 10% of the correct size for each line. The other 8 apps had optotypes that the study calculated were inaccurate by 11.9% to 39.9%.

    Such variance suggests a need for caution with patients referred by a nonophthalmologist who might have used a smartphone to check VA, said Dr. Perera. “It’s important not to expect the referral visual acuity to be especially accurate. You don’t know which app they’re using, and how accurate it was.”

    This study tested apps from 2012. Since then, more Snellen apps have appeared, including at least 1 that reportedly overcomes such problems.2

    —Linda Roach


    1 Perera C et al. Eye (Lond). 2015 May 1. [Epub ahead of print].

    2 Gounder PA, et al. www.journalmtm.com/category/articles/original-article/page/2/.


    Relevant financial disclosures: Dr. Perera—None.

    For full disclosures and disclosure key, see below.

    August 2015 News in Review Full Financial Disclosures


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