A prototype turns the distance between a face and a screen into an estimate of refractive error.
A diopter is the unit that describes the strength of a lens. People with myopia usually know their prescription exists, but few know what value it currently sits at, because the tools that measure it are clinical equipment. A 2019 paper in TELKOMNIKA proposed a different route: let a smartphone estimate the number.
The concept rests on a simple observable event. A person with myopia holds text at a comfortable distance, then slowly moves the phone closer until the letters stop being sharp. That point is the blur line. If the phone knows how far away the face is at that moment, it can convert the distance into a diopter value.
The distance method only works between 19 and 89 centimetres. That ceiling becomes a floor and a ceiling for the result, so the application can estimate from about minus 1.12 to minus 5.26 diopters. The user measures the right eye first with the left closed, then repeats the steps for the left eye.
Five participants tested the prototype, chosen using the common five user rule for usability work. They completed every task without failure and finished in an average of 2.03 minutes. The modified System Usability Scale gave a total score of 80.5, which counts as usable, with participants rating the language, instructions, and interface consistency highest.
The weakest item, at 2.20, was whether the result matched the participant's actual condition. Some users saw a different diopter value than their real prescription, which the authors list as a limitation and a subject for the next study.
Komang Candra Brata and Mukhammad Sharif Hidayatulloh (2019). An idea of intuitive mobile diopter calculator for myopia patient. TELKOMNIKA (Telecommunication Computing Electronics and Control).
