Comparison between Surgical Outcomes of LASIK with and without Laser Asymmetric Keratectomy to Avoid Conventional Laser Refractive Surgery Adverse Effects

Abstract

This study compared one-year postoperative outcomes of laser refractive surgery combined with laser asymmetric keratectomy (LAK) and laser in situ keratomileusis (LASIK)for myopia correction in middle-aged patients (aged 40-49 years) with a total corneal thickness deviation (summed across four directions) ≥ 80 microns. The control group (n = 26; 52 eyes) underwent LASIK; the comparison group (n = 26; 52 eyes) underwent combined laser refractive surgery and LAK. Age, spherical equivalence, uncorrected visual acuity (near and far), corneal irregularity on the Orbscan map, sum of corneal thickness deviations in four directions, corneal thickness distribution, distance between the maximum posterior elevation (best-fit sphere; BFS) and visual axis, and postoperative blurring scores were analysed retrospectively between the groups. Both groups had similar preoperative findings. Postoperatively, the sum of corneal thickness deviations in four directions (p = 0.000), distance between maximum posterior elevation (BFS) and visual axis (p = 0.003),blurring score (p = 0.001), and corneal irregularity in the 3.0 and 5.0 mm zones on the Orbscan map (p = 0.033 and p < 0.0001, respectively) were significantly lower in the comparison group (p = 0.000). LAK reduced total corneal thickness deviation, improved corneal symmetry, and reduced blurring scores significantly, one-year postoperatively. LAK could resolve shortcomings of LASIK, producing better surgical outcomes.

Figure 1

Operative principles of laser asymmetric keratectomy (biomechanical refractive correction). (a) Cornea with asymmetric thickness. (b) Deviations in the central symmetry of corneal thickness (analysed using Vision-Up software; red area). (c) Laser ablation for myopia correction, counterbalancing the myopic corneal curvature caused by ablation of central symmetry deviations, as predicted by the Vision-Up software (red area). (d) Cornea showing deviations in the central symmetry of corneal thickness after steps (b,c). (Source: ShapeVision Co., Korea).

Figure 2

An example for measuring the differences in thickness between symmetrically opposed points (0–180°, 45–225°, 90–270°, and 135–315°). The pachymetric map: 0–180°: 55 microns; 45–225°: 49 microns; 90–270°: 20 microns; 135315°: 24 microns; total: 148 microns. (Orbscan(B&L) Version 3.14).

Figure 3

Measuring the distance between the maximum posterior elevation (best-fit-sphere; BFS) and the visual axis. Corneal apex: temporally deviated (right upper red circle). The thinnest point (X, Y) is indicated by the lower red square (Orbscan(B&L) Version 3.14).

Figure 4

Changes in the distribution of corneal thickness between the preoperative and one-year postoperative time points.