Multivariate analysis of repeatability for the Near Eye Tool for Refractive Assessment (NETRA)

OBJECTIVE: To investigate repeatability of refractive state using a smartphone-based assessment tool, the Near Eye Tool for Refractive Assessment (NETRA). METHODS AND ANALYSIS: This study included 279 participants, predominantly female (66.7%) of African descent (49.1%). The age range was 9–63 years with mean age (s) 22.6 (8.9) years. Two consecutive measurements per eye with the NETRA were measured for both eyes of all participants. However, analyses for the right eyes only are included here. Multivariate statistical analysis included stereo-pair comets and scatterplots with 95% surfaces of constant probability density. Correlation coefficients for repeated samples were determined. Repeatability and agreement for NETRA were assessed with Bland-Altman plots, coefficients of repeatability ([Formula: see text] ; [Formula: see text] is the SD of differences) and intraclass correlation coefficients (ICCs). RESULTS: Bland-Altman plots, within-subject SD (s(w)), coefficients of repeatability and ICC indicated that repeated measurements were similar for many but not all eyes and there was good agreement (ICC=0.96) for the spherical coefficient (F(I)=M) but less so for antistigmatic coefficients (F(J)=J(0) and F(K)=J(45)) of power. Although mean differences for repeated samples were almost zero, 95% limits of agreement widths were larger for the stigmatic coefficients. Without cycloplegia, repeatability (2.77s(w)) was 1.63 D, 0.58 D and 0.56 D for the stigmatic and antistigmatic coefficients, respectively. CONCLUSION: NETRA is a potentially useful and inexpensive portable method in clinical and primary health settings, and especially in less-developed regions of the world. The subjective nature of the self-refraction task can be challenging for younger individuals, and cycloplegia is recommended for NETRA with such patients.