PURPOSE: The aim of this study was to quantify how closely the Nidek OPD-Scan objective refraction correlated with subjective refraction. METHODS: A retrospective audit of the preoperative refraction of 80 myopic and myopic astigmatic eyes before laser in situ keratomileusis (LASIK) or laser supepithelial keratomileusis (LASEK) was performed. Objective refraction in the 5-mm zone was performed using a Nidek OPD-Scan. Subjective refraction was performed by a senior optometrist. Statistical analysis of sphere, cylinder, and spherical equivalent refraction measurements was then performed. RESULTS: Spherical measurements correlated well with a linear regression equation, with a correlation coefficient of 0.97. Cylinder measurements correlated less well, with a correlation coefficient of 0.85. Spherical equivalent refraction measurements correlated well, with a correlation coefficient of 0.97. Analyzing the numerical difference between each objective refraction and its corresponding subjective refraction, the majority of values were only 0.50 D apart for sphere, cylinder, and spherical equivalent refraction. CONCLUSION: There was good correlation between objective OPD-Scan and subjective refraction, especially for sphere and spherical equivalent refraction measurements, with regression gradients and correlation coefficients close to 1.
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Yeung et al. (2004) studied this question.