eHealth tools for the self-testing of visual acuity: a scoping review.

Uncorrected refractive error is a major cause of vision impairment, and is indexed by visual acuity. Availability of vision assessment is limited in low/middle-income countries and in minority groups in high income countries. eHealth tools offer a solution; two-thirds of the globe own mobile devices. This is a scoping review of the number and quality of tools for self-testing visual acuity. Software applications intended for professional clinical use were excluded. Keyword searches were conducted on Google online, Google Play and iOS store. The first 100 hits in each search were screened against inclusion criteria. After screening, 42 tools were reviewed. Tools assessed near and distance vision. About half (n = 20) used bespoke optotypes. The majority (n = 25) presented optotypes one by one. Four included a calibration procedure. Only one tool was validated against gold standard measures. Many self-test tools have been published, but lack validation. There is a need for regulation of tools for the self-testing of visual acuity to reduce potential risk or confusion to users.