Abstract
Purpose :
We previously evaluated a smartphone app for refractive error measurement, which only measures spherical equivalent refraction. The app has now been modified for measuring astigmatism. This pilot study evaluates the feasibility of the new method.
Methods :
The app estimates myopic refractive error by measuring the far point distances for reading a modified astigmatism clock dial chart. For each eye, two far point distances, corresponding to two perpendicular directions of lines respectively, are estimated by the phone camera. The astigmatism power is calculated based on the difference between the two distances. In total 42 college students with myopia were enrolled. The range of spherical refractive error was -0.13 to -9D (mean±STD: -3.1D+/-2.3D). The app measurement was compared with noncycloplegic subjective refraction measurement.
Results :
One subject with a spherical of -9D in both eyes, could not be measured. For the remaining 82 eyes included, the range of astigmatism was 0 to -2.75D (mean±STD: -0.79D±0.62D) according to subjective refraction. The mean absolute error of the app measurement was 0.54D. The median of app error was 0.15D (IQR: -0.25D to 0.48D). Spherical refraction was also derived from the far point distances. Linear regression showed that the app measurement was significantly correlated with clinical measurement (R-square = 0.93). The slope of the regression was 0.94, which indicates that on average the two measurements were highly consistent.
Conclusions :
This proof-of-concept study shows that it is feasible to measure astigmatism based on two far point distances for astigmatism clock dial chart. It is crucial to locate the far points where the subject perceives the lines clearly, but there is an uncertainty in each individual’s criteria for sharpness. Further investigation is needed to improve the objectivity of judgment.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.