Corneal epithelial healing and surgically–induced aberrations after excimer laser correction

Abstract

Abstract: : Purpose: To predict wavefront aberrations associated with epithelial healing after laser in–situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) and develop advance healing adjusted ablation (AHAA) patterns to minimize these aberrations. Methods: Simulation of laser correction of combined myopia, astigmatism, higher order aberrations were performed in a computer. Six–mm optical zone diameter and variable transition zones were used. Post–surgical deviations from intended correction are calculated based on a previously published mathematical model of the smoothing action of epithelial healing. A constrained iterative deconvolution technique was used to design AHAA patterns. Results: The simulated corrections produced complex patterns of secondary aberrations and only the dominant terms are summarized here. Correction of –6 D myopia produced undercorrection of myopia, oblate spherical aberration (S.A., 1.0 micron Z₄⁰). The addition of 3 D astigmatism induced tetrafoil (0.5 micron Z₄²). The additional correction of SA induced myopic/hyperopic shift depending on if the SA is prolate or oblate. The additional correction of coma induced pentafoil. We were able to design AHAA patterns to exactly cancel the healing induced aberration. Conclusions: Our model predicts that laser ablation to correct myopia and astigmatism predictably induce un–intended secondary aberrations, in agreement with published clinical results. Wavefront–guided correction of aberrations also induces significant un–intended deviations. We developed an AHAA algorithm that can theoretically compensate for these secondary deviations and improve the outcome of both spherocylindrical and wavefront–guided laser corrections.

Keywords: refractive surgery: optical quality