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A Mirshahi, D Gerhardt, J Buehren, G Wellermann, GW K Steinkamp, T Kohnen; Differences Between Objective and Subjective Refractions Before and After LASIK: Impact of Optical Zone on Accuracy of Results . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4156.
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Purpose:To investigate the accuracy of automated objective refraction before and after laser in situ keratomileusis (LASIK) for treatment of myopia and myopic astigmatism. Methods:Retrospective analysis of patient data following LASIK surgery with a corrected visual acuity of at least 20/40. 250 eyes (132 patients, mean age: 37 y) were refracted before and one month after surgery, objectively with a Topcon RM A-2300 autorefractor (OR) and subjectively using a phoropter (SR). The data set was divided into four groups with different optical zones (a: 5 - 5.5, b: 5.6 - 6.0, c: 6.1 - 6.5 and d: 6.6 - 7.0 mm). Wilcoxon matched pairs signed rank test was used for statistics. Results:The mean spherical equivalent of subjective and objective refractions was -6.59 ±2.69 and -6.46 ±2.58 preoperatively, and -0.32 ±0.86 and -0.62 ±0.93 postoperatively (table 1). Similar results were found when subdividing the data into 4 groups with low (≤ 3 D, corresponding to group d), moderate (≤ 6 D, corresponding to c), high (≤ 9 D, corresponding to b) and very high myopia (≷9 D, corresponding to a). Conclusion:Following LASIK, automated refractometry is less accurate than in unoperated myopes. The accuracy of OR is influenced by laser optical zone size and preoperative amount of myopia. The lower the optical zone and the higher the myopia, the greater is the difference between OR and SR, with the autorefractor determining more myopic results. Objective refraction is not sufficient to determine the accurate value of the refractive error following excimer lamellar surgery. table 1 View OriginalDownload SlideView OriginalDownload Slide
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