Systematic measurement errors involved in over‐refraction using an autorefractor (Grand‐Seiko WV‐500): is measurement of accommodative lag through spectacle lenses valid?

Abstract

Lags of accommodation in ametropic children are often evaluated through spectacle lenses (over-refraction). This study investigated the validity of over-refraction when using an autorefractor. Using an autorefractor (Shin-Nippon SRW-500/Grand-Seiko WV-500), refractive readings were obtained in 25 cyclopleged eyes (mean +/- S.D. refraction: -3.44 +/- 3.56 D, range: from -10.56 to +0.25 D) while placing spherical lenses of different power (from -5.00 to +5.00 D) in front of the eye at a vertex distance of 12 mm. Based on the refractive readings with and without the lens, and the lens power, measurement errors were estimated. Similarly, the measurement errors were estimated also in model eyes of -10.00, -4.75, 0.00 and +10.00 D. The results were compared with ray-tracing simulations based on the internal specifications of the autorefractor. Measurement errors were found unless the power of the spectacle lens was equal to the refractive error of the eye. When the spectacle lens power was greater (less myopic or more hyperopic) than the refraction of the eye, the measurement error was negative in sign and greater than -0.3 D. It follows that, when an accommodative response is measured in myopic subjects, the refractive reading usually becomes more myopic than the refraction of the eye including the accommodative response; hence, the accommodative response is overestimated, and the lag of accommodation is underestimated. The autorefraction through spectacle lenses involved systematic measurement errors. The extent of the errors is usually small but needs to be taken into account in a comparative study of accommodative responses among different refractive groups.