Autorefraction/Autokeratometry and Subjective Refraction in Untreated and Photorefractive Keratectomy-Treated Eyes

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Abstract
Objective: To examine the relative accuracy of autorefraction and autokeratometry (autorefraction/autokeratometry) and subjective refraction in untreated and photorefractive keratectomy (PRK)—treated eyes. Design: Results of autorefraction/autokeratometry obtained by means of 2 contemporary devices (Nidek ARK 2000 and Canon RK-3) were compared with those of subjective refraction in 48 untreated eyes and in 78 eyes treated with (PRK). Results: A trend toward greater differences between subjective and objective methods in PRK-treated eyes was observed. Both autorefraction devices showed similarly higher differences from subjective readings in PRK-treated eyes with regard to sphere (P<.001) and cylinder (P=.02), but not axis (P=.4). For autokeratometry, the mean difference from manual readings was highly significant when all K readings were considered together, but not so for the individual differences in keratometric astigmatism (Canon RK-3 and Nidek ARK 2000 vs manual results: P=.03 and P=.93, respectively) and keratometric axis (Canon RK-3 and Nidek ARK 2000 vs manual results: P=.88 and P=.19, respectively). Conclusions: Refractive and keratometric readings obtained with the automated devices tested in this study varied more from those obtained with subjective methods when the eyes examined had been treated with PRK. Corneal topographical changes inherent in the wound-healing process may influence objective measurement with automated devices.