A Novel Approach to Enhancement Linked Laser Asymmetric Keratectomy Using Semi-Cylindrical Ablation Pattern in Patients with Myopic Regression After Laser Refractive Surgery

Abstract

Purpose: We aimed to introduce a new technique to reduce regional asymmetry of corneal thickness by assessing its effectiveness in four patients with myopic regression after laser refractive surgery (LRS).

Patients and methods: Four patients (four eyes) with myopic regression after LRS were included in this study. A new technique of enhancement with laser epithelial keratomileusis-linked laser asymmetric keratectomy using semi-cylindrical ablation pattern (E-LAK-SCAP) with full integration of the Vision-Up software for analyzing the corneal thickness deviation can be used to create central symmetry by blocking laser ablation on the thin cornea. It reduces the regional asymmetry of the corneal thickness, thus improving corneal symmetry and correcting the refractive power and myopic shift due to E-LAK-SCAP. We measured refraction, visual acuity, intraocular pressure (IOP), central corneal thickness (CCT), corneal irregularities in the 3.0mm, and 5.0 zones on Orbscan maps, the sum of corneal thickness deviations in four directions (SUM), distance between the maximum posterior elevation (best-fit-sphere [BFS]) and the visual axis (DISTANCE), and angle kappa before and after LRS and E-LAK-SCAP. Blurring scores were measured before and after E-LAK-SCAP.

Results: The uncorrected far visual acuity (LogMAR) increased after LRS and E-LAK-SCAP. SUM (µm) increased after LRS in three cases, but decreased in all four cases after E-LAK-SCAP. DISTANCE increased after LRS, but decreased after E-LAK-SCAP. The spherical equivalent, CCT, decreased after LRS and E-LAK-SCAP. Blurring scores decreased after E-LAK-SCAP, and angle kappa was similar before and after LRS, but decreased after E-LAK-SCAP. IOP was similar before and after both LRS and E-LAK-SCAP.

Conclusion: E-LAK-SCAP improved corneal symmetry by reducing the SUM and DISTANCE, showing good postoperative visual acuity, and blurring was reduced postoperatively. There was no myopic regression in the one-year postoperative period.

Keywords: E-LAK-SCAP; LRS; myopic regression; regional asymmetry of corneal thickness.

Figure 1

Pre-LRS Orbscan map of case 1. Right bottom shows a pachymetric map: an example of measuring the differences in thickness between symmetrically opposed points is shown on the pachymetric map (0–180°, 45–225°, 90–270°, and 135–315°): 0–180°: 39 µm; 45–225°: 44 µm; 90–270°: 33 µm; 135–315°: 3 µm; total: 119 µm. Right top map: 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, and the posterior high on thicker cornea, and front elevation on the thinner cornea is also shown.

Figure 2

Pre-E-LAK-SCAP (post-LRS) Orbscan map of case 1. Right bottom pachymetric map: an example of measuring the differences in thickness between symmetrically opposed points is shown on the pachymetric map (0–180°, 45–225°, 90–270°, and 135–315°): 0–180°: 60 µm; 45–225°: 60 µm; 90–270°: 21 µm; 135–315°: 6 µm; total: 147 µm. Right top map: shows the measured 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.

Figure 3

Post-E-LAK-SCAP Orbscan map of case 1. Right bottom pachymetric map: an example of measuring the differences in thickness between symmetrically opposed points is shown on the pachymetric map (0–180°, 45–225°, 90–270°, and 135–315°. 0–180°: 4 µm, 45–225°: 5 µm, 90–270°: 28 µm, 135–315°: 41 µm, total: 78 µm). Right upper map: the measured distance between the maximum posterior elevation (best-fit-sphere; BFS) and the visual axis is also shown. Corneal apex: centrally located (right upper red circle). The thinnest point (X, Y) is indicated by the lower red square.

Figure 4

The schematic description of LAK-SCAP. (A) shows examples of axial, symmetric images of two-partial ablation patterns. (B) shows examples of laser ablation patterns for LAK-SCAP; specifically, it shows one partial ablation for existing cylindrical ablation patterns, as seen in (A). These patterns can be achieved by blocking laser corneal ablations at the thinner sections of the cornea.

Figure 5

Ablation pattern of case 1: Purple circled round area indicates ablation pattern (total =5.50 diopters) of both refractive error (−4.0 diopters) and myopic shift (−1.50 diopters) due to LAK-SCAP, and red dotted circled area indicates LAK-SCAP on the thicker area of the cornea.

Figure 6

Differential pachymetric map by Orbscan II (Bausch & Lomb, Bridgewater, NJ, USA) between pre- and post-E-LAK-SCAP in case 1.