Preliminary Evaluation of Spherical Over-Refraction Measurement Using a Smartphone

Background: Smartphones offer a promising tool for monitoring refractive error, especially in underserved areas where there is a shortage of eye-care professionals. We propose a novel method for measuring spherical over-refraction using smartphones. Methods: Specific levels of myopia using positive spherical trial lenses, ranging from 0.00 D to 1.50 D in 0.25 D increments, were induced in 30 young participants (22 ± 5 years). A comparison was conducted between the induced over-refraction and the measurements obtained using a non-commercial mobile application based on the face–device distance measurement using the front camera while the subject was performing a resolution task. Results: Calibrated mobile app over-refraction results showed that 89.5% of the estimates had an error ≤ 0.25 D, and no errors exceeding 0.50 D. Bland–Altman analysis revealed no significant bias between app and clinical over-refraction, with a mean difference of 0.00 D ± 0.44 D (p = 0.981), indicating high accuracy and precision of the method. Conclusions: The methodology used shows high accuracy and precision in the measurement of the spherical over-refraction with only the use of a smartphone, allowing self-monitorization of potential myopia progression.