THE REPEATABILITY OF AUTOMATED AND CLINICIAN REFRACTION

Purpose. Auto-refractors are used as a starting point for clinicians' refractions and in studies of refractive error. We investigated the re peatability of the Hoya AR-570 and clinician refraction. Methods. Eigh ty-six subjects, aged 11 to 60 years, were recruited by mailing inquir ies to 500 randomly selected patients who had received recent examinat ions at the University of California Optometric Eye Center. Contact le ns wearers, patients with best corrected visual acuity worse than 20/3 0 in either eye, and patients with a history of diabetes were excluded . Each subject was examined by two clinicians during one visit. The fi rst clinician obtained five auto-refractor readings for each eye (whic h were later averaged), performed a balanced subjective refraction (wi th spherical masking lenses in the phoropter), and repeated the automa ted refractor measurements. This protocol was then repeated by the sec ond clinician. Clinicians were randomized with regard to testing order and masked to automated refractor results, each other's refractions, and previous spectacle prescriptions. Results. To quantify repeatabili ty, we used mixed model analyses of variance to estimate the appropria te variance components while accounting for the correlation among, for example, repeated measurements of the same eye. Astigmatic data were analyzed by converting into Fourier form: two cross-cylinders at axis 0 degrees (J(0)) and axis 45 degrees (J(45)). For mean spherical equiv alent, the average difference between five averaged automated refracto r readings, taken by two different optometrists, was +0.02 D (95% limi ts of agreement = -0.36 to +0.40 D). The average difference between th e two optometrists' subjective refractions was -0.12 D (95% limits of agreement -0.90 to +0.65 D). The 95% limits of agreement for the autom ated refractor were about half those of the clinician for both astigma tic terms (J(0) and J(45)) and for all comparisons. Conclusions. Autom ated refraction is more repeatable than subjective refraction and ther efore more appropriate for studies of myopia progression.