|Title||Preliminary Clinical Evaluation of a Smartphone App for Measuring Strabismus|
|Author, Co-Author||Shrinivas Pundlik, Rui Liu, Matteo Tomasi, Kevin Houston, Hong Liu, Gang Luo|
Purpose: A smartphone app based on the Hirschberg method to measure eye misalignment was previously assessed in a laboratory setting for phoria and eye deviations measurements in non-strabismic people. In this pilot study, the app was evaluated for measuring strabismus in clinic.
Methods: The app captures 40 frames within 2 seconds during a unilateral cover-uncover of the non-dominant eye. It computes displacement of the corneal reflection in pixels and converts to prism diopters to provide strabismus measurement. Sixteen strabismic patients (age: 6 to 46, median 11, IQR 19) were enrolled from Shanghai Eye and ENT hospital. Their eye alignment was measured using unilateral cover test with prism neutralization method (PN) and with the app. Data from the app was unavailable for 2 subjects: one due to app failure and the other due to operator error.
Results: The range of deviations measured by PN was exotropia 60 Δ to esotropia 30 Δ, with 9 intermittent strabismus cases. The app measurements were correlated with the PN (R2 = 0.93, p < 0.0001), but lower than PN (slope of the line fit was 0.8). The median and IQR of the absolute difference between app and PN were 4.7 and 4.3 Δ, respectively. The difference was greater for larger deviations (deviations ≤ 20 Δ: median = 3.4 Δ, IQR = 3.1 Δ; deviations > 20 Δ: median = 8.5 Δ, IQR = 5.5 Δ).
Conclusion: The app showed strong correlation with clinical measurements, but the average app measurements were lower. One of the possible reasons may be that the actual deflection power of the prism, especially for high power ones, can be less than nominal power depending on the incidence angle (Jung, Peli, 2014). Further clinical trials are warranted.
Jung JH, Peli E (2014) Impact of high power and angle of incidence on prism corrections for visual field loss. Optical Engineering, 53 (6), 061707, 2014;
|Affiliation of Co-Authors||Shanghai Eye and ENT Hospital, Fudan University, Schepens Eye Research Institute, Mass Eye and Ear, Schepens Eye Research Institute, Mass Eye and Ear, Shanghai Eye and ENT Hospital, Fudan University, Schepens Eye Research Institute, Mass Eye and Ear|