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JE Gwiazda, C Weber; Comparison of Spherical Equivalent Refraction and Astigmatism Measured With Three Different Models of Autorefractors . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1505.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To compare refractive measurements taken with three different autorefractor models. Methods:The refractive error of each eye of fifty adults aged 17 to 59 years (mean = 30.5 yrs) was measured without cycloplegia using the Canon R-1 and two newer instruments, the Grand Seiko WR-5100K and the Nidek ARK 700-A. For the first two, an isolated line of 20/100 letters on the ETDRS chart at 4.0 m served as a target, while for the Nidek the subject looked at a picture of a balloon in the instrument. Five readings were taken for each eye, and the data (sphere, negative cylinder power, and axis) were analyzed using Fourier decomposition of the power profile. Each reading was broken down into three components, the spherical equivalent and two Jackson crossed cylinder vectors, J0 and J45. Right eye results are reported. Results:Overall, the mean spherical equivalent was more hyperopic with the Seiko, by 0.43D relative to the Canon and by 0.65D relative to the Nidek. Correlation of the spherical equivalents for each pair of instruments was 0.99. Both mean J0 and J45 were the same for the Nidek and Seiko, with correlations of 0.97 between the two instruments for each of the two components. For J0 the Canon was more minus than the other two instruments by 0.14D, and on this component the correlation of the Canon with each of the other two was 0.87. J45 measured by the Canon was more positive than the other two by 0.06D. For J45 the correlation of the Canon with the Seiko was 0.40 and with the Nidek was 0.38. The Canon showed more astigmatism than the other two. The mean of the absolute values of the cylinder power differences was 0.40D between the Canon and the Nidek, and 0.43D between the Canon and the Seiko. This mean difference between the Nidek and Seiko was 0.10D. Conclusion:The Seiko provided more hyperopic readings than the Canon and the Nidek. Measurements of astigmatism taken by the Nidek and the Seiko showed good agreement, while the Canon measured more astigmatism that did not correlate well with the other instruments. If the Seiko is used in place of the older Canon, the differences in spherical equivalent and astigmatism must be considered.
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