Higher order aberrations with aspheric ablations using the Nidek EC-5000 CX II laser.

PURPOSE: To analyze the change in higher order aberrations in myopic and myopic astigmatic eyes following an aspheric ablation profile for laser in situ keratomileusis (LASIK) using a Nidek EC-5000 CX II excimer laser system. METHODS: We performed a retrospective audit of 38 eyes (19 patients) with myopia and myopic astigmatism. A customized aspheric transition zone profile (CATz) was used in all eyes (profile 4) with an ablation zone of 5 mm and a transition zone of 9 mm using FinalFit software and a Nidek EC-5000 CX II excimer laser system. RESULTS: Mean higher order aberrations (RMS) increased from 0.42 microm at baseline to 0.57 microm at 6-month follow-up. Mean spherical aberrations (Z12) increased from 0.02 microm at baseline to 0.33 microm after LASIK. Mean spherical aberration defocus equivalent (DEQ) increased from 0.56 microm at baseline to 1.54 at 6 months after surgery. Mean trefoil (Z6) was -0.11 microm at baseline and -0.14 microm at the 3-month examination. Mean coma (Z7) was -0.09 microm at baseline and -0.10 microm after surgery. Mean coma (Z8) was -0.03 at baseline and 0 at the 3-month examination. Mean trefoil (Z9) was -0.03 at baseline and -0.12 at the 3-month examination. CONCLUSION: The amount of postoperative higher order aberrations in these myopic eyes was acceptable. However, the clinical significance of these numerical changes in aberrations is not known.

Correlation of Nidek OPD-Scan objective refraction with subjective refraction.

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.