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Intraocular lens power calculation after myopic laser in situ keratomileusis: Estimating the corneal refractive power
Shady T Awwad1, Christian Manasseh, R Wayne Bowman
1Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9057, USA.
Purpose:
To derive regression-based formulas and identify essential dependent variables to estimate refractive corneal power after myopic laser in situ keratomileusis (LASIK).
Setting:
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.
Methods:
A retrospective data review of 30 eyes (23 patients) having myopic LASIK followed by phacoemulsification and posterior chamber intraocular lens (IOL) implantation in the same eye gathered the following: pre-LASIK and post-LASIK refractions and topographies, axial length, IOL type and power, and spherical equivalent (SE) refraction 3 months after phacoemulsification. Using the double-K Holladay 1 formula, the refractive corneal power in each eye was back-calculated. Regression formulas were derived and compared with current corneal power estimation methods.
Results:
The multiple regression formula based on the average corneal power in the central 3.0 mm area (ACCP3 mm) and the change (Delta) in SE (SEpostLASIK-SEpreLASIK) was simplified to ACCPadj=ACCP3mm-0.16DeltaSE, with the highest Pearson correlation coefficient (r=0.989) and lowest absolute corneal power estimation error (0.30 diopter [D]+/-0.30 (SD)). Regression based on ACCP3 mm alone yielded 0.980 and 0.49+/-0.40 D, respectively. Using SimK with DeltaSE resulted in a lower r value (0.971) and larger absolute corneal power estimation error (0.65+/-0.44 D) (P=.0014). The clinical history methods yielded 0.909 and 1.09+/-0.868 D, respectively (P=.0005).
Conclusion:
The regression formula based on ACCP3mm and DeltaSE was very accurate in predicting refractive corneal power after myopic LASIK followed by formulas based on ACCP3mm alone and SimK and DeltaSE, all of which consolidate the validity of similar previously suggested methods, including EffRPadjusted.
