Comparison of simulated keratometric changes induced by custom and conventional laser in situ keratomileusis after myopic ablation: retrospective chart review.

Purpose: To determine the relationship between the achieved refractive change and the change in simulated keratometry (K) after myopic laser situ keratomileusis (LASIK) and compare this relationship between custom and conventional treatments.

Setting: Department of Ophthalmology, University of California, Davis, Sacramento, California, and John A. Moran Eye Center, Salt Lake City, Utah, USA.

Methods: The change in simulated K and the refractive change induced by custom myopic LASIK and conventional LASIK were determined. The relationship between the variables was analyzed by regression methods.

Results: Custom treatment was performed in 106 eyes and conventional treatment in 224 eyes. Simple linear regression analysis did not fit the clinical observation when the refractive change was less than 2.00 diopters (D) of myopic correction with both treatments. Under the linear model and nonlinear model, each unit of refractive change yielded a greater change in corneal topographic power with custom treatment than with conventional treatment. With both treatments, the rate of change in simulated K was not constant and was much more variable with lower amounts of correction. The relationship was more constant and linear with larger amounts of refractive correction.

Conclusions: The relationship between the measured change in simulated K and the induced refractive change better fit a nonlinear relationship with smaller amounts of refractive correction in custom LASIK and conventional LASIK. Under all forms of analysis, custom treatments yielded a greater per-unit change in corneal curvature than conventional treatments, especially for refractive corrections of 4.00 D and higher.