Does the Accuracy and Repeatability of Refractive Error Estimates Depend on the Measurement Principle of...

The purpose of this study was to determine the accuracy and repeatability of refractive errors obtained using three autorefractors based on different measurement principles, vis-à-vis, gold-standard retinoscopy.

Accuracy of noncycloplegic, sphero-cylindrical refractive error of 234 eyes was obtained using the rotary prism-based RM-8900 closed-field autorefractor, photorefraction based Spot vision screener, wavefront aberrometry based E-see, and streak retinoscopy by four different examiners, masked to the results of each other. Intersession repeatability of autorefractors was determined by repeat measurements in a subset of 40 subjects.

Retinoscopy values of M, J₀, and J₄₅ power vectors for the cohort ranged from -10.2 to 8 D, -1.4 to 1.8 D, and -0.9 to 1.2 D, respectively. Across autorefractors, the interequipment bias of M and J₀ power vectors were statistically insignificant (< ±0.5 D; P > 0.05) but the corresponding limits of agreement were ±2.5 and ±1 D, respectively, without any trend across instruments or the patient's age (P > 0.5). Repeatability of M and J₀ power vectors were ±0.75 D and ±0.40 D, respectively, across autorefractors. The range of J₄₅ power vector was too narrow for any meaningful analysis.

Refractive errors measured using autorefractors operating on different principles show minimal bias and good short-term repeatability but relatively large agreement limits, vis-à-vis, retinoscopy. Among them, the wavefront aberrometry based E-see autorefractor performs relatively better in all measurement parameters evaluated here.

Although autorefractor estimates of noncycloplegic refractive error appears independent of their measurement principle, their relatively poor agreement with gold-standard retinoscopy warrants caution while used for screening and quantification of refractive errors.