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A. A. Stratos, G. A. Kounis, G. D. Kymionis, J. A. Moschandrea, V. F. Diakonis, S. I. Panagopoulou,, M. A. Grentzelos, D. M. Portaliou, I. G. Pallikaris; Multiple Linear Regression Analysis of Refractive Surgery Outcomes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4192.
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The purpose of this study is the development of a regression model that would predict the residual refractive error based on certain preoperative factors, including the time of application of Mitomycin-C, intraoperatively in PRK procedures.
In this retrospective study, 186 patients (340 eyes) who underwent PRK with Mitomycin-C for the correction of myopia and astigmatism were included. All patients underwent cycloplegic refraction at three months postoperatively.For the data analysis, the term "Defocus Equivalent Refraction" was used in order to include in our sample all cases that indeed, presented residual refractive error.A multiple linear regression (Stepwise method, SPSS17) was fitted to assess possible predictors of post-op residual refractive error. The explanatory variables in the model were: age, central corneal thickness (CCT), attempted correction of myopia and astigmatism and Mitomycin-C time of application. The respective means-ranges were: 31±7 (19 to 61y), 542±33 (472 to 620µm), -4,32±2,10 (-0,50 to -10,50D), -0,85±0,95 (0 to -6,0D), 18±15 (0 to 90sec).
From the data analysis an overcorrection in patients who underwent PRK-MMC for the correction of myopia and astigmatism was evident (RemainingDefocus: 0,79±0,55 (0 to 3,7D).Based on the results of the multiple linear regression, the residual refractive error depends on attempted correction and time of application of Mitomycin-C but not on age and CCT. The equation for the regression model is:RemainingDefocus = 0,379 - 0,048 * AttemptedSph - 0,080*AttemptedCyl + 0,005*MMCtime.
An overcorrection in patients who underwent PRK-MMC is evident (Figure). The residual refractive error after PRK-MMC is related to the attempted correction (amount of myopia and astigmatism corrected) and the time of application of MMC.The equation of multiple linear regression analysis can be used as a nomogram in order to ensure the accuracy of the results outcome.
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