Comparison of a Novel Cell Phone-Based Refraction Technique (NETRA) With Objective Clinical Retinoscopy

Abstract

Purpose: : Uncorrected refractive errors are the largest cause of avoidable blindness in developing countries. The effectiveness of population-based vision screening programs significantly enhanced if a rapid, cost-effective and quantitative method for estimating the refractive-errors is available. A novel cell-phone based technique (NETRA) has been designed to rapidly quantify the refractive-error status of the eye. This study determined the accuracy and precision of this prototype device in determining spherical refractive error in adults, in comparison to gold-standard objective retinoscopy.

Methods: : The optical setup of NETRA consists primarily of a pinhole mask and is retrofit on a high-resolution cell phone (Samsung Behold II^TM) that displays a spatially resolved pattern of red-green lines to the subject. Refractive error is estimated by subjectively aligning the red-green patterns using a custom-designed user-interface on the cell phone. In this study, cycloplegic spherical refractive errors (SR) of the dominant eye of 29 adults (mean ± SD age: 23.1 ± 2.6yrs), with best-corrected visual acuity of 20/20, were measured thrice using the NETRA and averaged. SE of the same eye was also determined using objective restinoscopy performed by an experienced Optometrist.

Results: : Cycloplegic SR of the subjects ranged from -6.25D to +3.00D. The SR determined by NETRA was well correlated with that of objective retinoscopy (r=0.96) and the two measures were not statistically significantly different from each other (p=0.14). Orthogonal linear regression fit to the plot of SR determined by NETRA against those determined by retinoscopy had a slope of 0.86 and a y-intercept of -0.22D. The mean (± 1SD) deviation for the three measures of SR determined by NETRA across all subjects was 0.18 ± 0.15D.

Conclusions: : When compared to objective retinoscopy, NETRA slightly underestimated the myopic and hyperopic cycloplegic refractive errors and had a small myopic offset of 0.22D. NETRA estimated myopic and hyperopic refractive errors with a mean precision of 0.18D. These suggest that NETRA could be used as an effective tool for rapidly estimating refractive errors in a vision-screening program. Accuracy of this novel prototype device in estimating refractive errors is expected to increase as technology evolves.

Keywords: refraction • clinical (human) or epidemiologic studies: systems/equipment/techniques • clinical research methodology