A Comparison of Autorefractor Performance
Purpose: To compare the agreement between subjective refraction and autorefraction using two commercially available autorefractors.
Methods: Prospective data were collected for 190 subjects using either the Nidek ARK-700A (Fremont, CA) or the Topcon KR-8000 (Paramus, NJ) and subjective refraction (masked to autorefraction). Refractions were compared in terms of spherical equivalent using Bland-Altman limits of agreement and astigmatic vector difference using median and 95th percentile.
Results: The two groups were similar for age, gender, spherical equivalent, and astigmatic power. The differences in spherical equivalent between subjective and autorefraction were significantly different (mean ± SD; Nidek, -0.03 ± 0.36 D; Topcon, +0.11 ± 0.34 D; analysis of variance, F = 7.84; p < 0.01). However, the 95% limits of agreement were similar: Nidek, -0.74 to +0.68 D; Topcon, -0.55 to +0.77 D. The median differences in astigmatic vector difference were also similar: Nidek, 0.27 D and Topcon, 0.25 D. However, the 95th percentile was 0.67 D for Nidek and 1.09 D for Topcon. There was a low frequency of large (>1.00 D) differences in spherical equivalent, 1.1% with each autorefractor. There were five cases with astigmatic vector difference >1 D, all with the Topcon KR-8000 (5.3%).
Conclusions: Both autorefractors show excellent agreement with subjective refraction. Despite a statistically significant difference in mean spherical equivalent (0.14 D), near identical limits of agreement (0.10 D difference) suggest clinical equivalence. Conversely, for astigmatism, despite similar median scores, major outliers were more likely with the Topcon, reflected in a 0.42 D larger 95th percentile, which suggests a small advantage for the Nidek for avoiding large astigmatic errors.
Key Words: autorefractor, autorefraction, refraction, spherical equivalent, vector analysis
Optometry & Vision Science. 81(7):554-558, July 2004
PESUDOVS, Konrad PhD, FAAO; WEISINGER, Harrison Scott PhD
Accepted for publication 12 January 2004
© 2004 American Academy of Optometry
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