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Here we present a mobile application that accurately determines the distance between an optical sensor and the human corneal limbus for visual acuity assessment. The application uses digital image processing and randomized circle detection to locate the cornea. Then, a reference scaling measurement is employed to calculate distance from the sensor to a user. To determine accuracy and generalizability, testing was conducted both with 200 static images, 25 images each of males and females for four ethnic groups from a facial image database, and live image streams from a test subject. Average absolute corneal radius error over 10 trials for the static images was 6.36%, while average absolute distance error for the live image streams was less than 1%. Subsequently, distance measurements were used to scale letter sizes for a Snellen Chart-based visual acuity assessment. This system enables monitoring of chronic retinal diseases, as patients can quickly and accurately measure their visual acuity through the mobile eye exam suite.


Neal A Patel, Perry N Alagappan, Chuanbo Pan, Peter Karth. A mobile vision testing application based on dynamic distance determination from the human corneal limbus. Health informatics journal. 2020 Dec;26(4):3037-3055

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PMID: 32993413

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