Intraocular lens power calculation after myopic laser in situ keratomileusis: Estimating the corneal refractive power
Accepted 25 March 2008.
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 (ACCP3mm) and the change (Δ) in SE (SEpostLASIK − SEpreLASIK) was simplified to ACCPadj = ACCP3mm − 0.16ΔSE, 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 ACCP3mm alone yielded 0.980 and 0.49 ± 0.40 D, respectively. Using SimK with ΔSE 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 ΔSE was very accurate in predicting refractive corneal power after myopic LASIK followed by formulas based on ACCP3mm alone and SimK and ΔSE, all of which consolidate the validity of similar previously suggested methods, including EffRPadjusted.
From the Department of Ophthalmology (Awwad, Bowman, Cavanagh, Verity, Mootha, McCulley), University of Texas Southwestern Medical Center, Dallas, Texas, and the System Engineering Division (Manasseh), University of California at Berkeley, Berkeley, California, USA; the Department of Ophthalmology (Awwad), American University of Beirut Medical Center, Beirut, Lebanon
Corresponding author: James P. McCulley, MD, Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9057, USA.
Dr. McCulley is a consultant to Alcon Laboratories, Fort Worth, Texas, USA. No author has a financial or proprietary interest in any material or method mentioned.
Supported in part by an unrestricted grant from Research to Prevent Blindness, New York, New York, USA.
ABSTRACT