Effect of the Optical Zone Ablation Diameter on Higher Order Aberrations After Transepithelial Photorefractive Keratectomy: A Cohort Study

Abstract

Objectives: To study the effect of the optical zone diameter of ablation on higher order aberrations after transepithelial photorefractive keratectomy for myopia and myopic astigmatism.Methods: In this historical cohort study in 2019, patients were grouped into 7-mm (Gr-1) and 6.5-mm optical zones of ablation (Gr-2). Topographic and higher order aberrations at analysis diameters of 2, 4, and 6 mm were measured before and six months after transepithelial photorefractive keratectomy. The changes in the five types of higher order aberrations in the 6.5 mm and 7 mm groups were compared. The pupillary diameter was correlated with the change in the higher order aberrations.Results: We had 24 eyes of 12 patients in Gr-1 and 80 eyes of 40 patients in Gr-2. The trefoil type of higher order aberrations at 6 mm was significantly more prevalent in Gr-2 than in Gr-1 before surgery (p = 0.038). The change in spherical aberration six months after surgery compared with before was significantly more at 6 mm in the eyes of Gr-2 patients (p = 0.02). For the eyes managed by the 7-mm optical zone of ablation for transepithelial photorefractive keratectomy, the decline in the different types of higher order aberrations was significant. The pupillary diameter was positively correlated with the change in the third-order coma in Gr-2 (Spearman coefficient, p = 0.005). All the eyes had an uncorrected visual acuity of 0.0 LogMAR in Gr-1 and 95% in Gr-2 after surgery.Conclusions: The higher order aberrations six months after transepithelial photorefractive keratectomy were similar in eyes managed with 7-mm and 6.5-mm optical zone for ablation. But a lower aberration coefficient in eyes was managed by the 7-mm zone than the 6.5-mm zone of optical ablation at 6-mm analysis diameter.

Changes in Corneal Dynamics and Effective Optical Zone After Transepithelial Photorefractive Keratectomy for Myopia

“…Al-Mohaimeed noticed that HOAs increased to some extent 6 months after T-PRK ( 15 ). Ozulken and Gokce reported an increase in spherical aberration 6 months after PRK in their study including 15 high myopic eyes also ( 17 ).…”

“…Prior PRK studies have evaluated the correlation between the corneal high-order aberrations (HOAs) and the size of the programmed optical zone ( 15 - 17 ). However, none of these studies evaluated the relationship between HOAs – corneal parameters and regression in the EOZ diameter in comparison to the programmed optical zone.…”

“…Transepithelial photorefractive keratectomy (T-PRK), one of the most popular corneal refractive surgical methods, can be used to treat myopia and increase patient comfort (2,3). All-surface laser ablation (SCHWIND eye-tech-solutions GmbH & Co. KG, Mainparkstrasse, Kleinostheim, Germany) used in T-PRK Prior PRK studies have evaluated the correlation between the corneal high-order aberrations (HOAs) and the size of the programmed optical zone (15)(16)(17). However, none of these studies evaluated the relationship between HOAscorneal parameters and regression in the EOZ diameter in comparison to the programmed optical zone.…”

Limitations of and Solutions to Using 6 mm Corneal Spherical Aberration and Q Value after Laser Refractive Surgery

“…The continued use of a 6 mm area value as a standard metric in many papers might be attributed to the limited data provided by the measuring equipment and a lack of knowledge and understanding among ophthalmologists regarding their interpretation and utilization. Finally, this study highlights the need for a method to compare the obtained corneal SA and asphericity in various areas of the cornea with normal values and to confirm changes before and after surgery to address the limitations of existing methods [30][31][32].…”