Comparison of refractive outcomes after photorefractive keratectomy with different optical zones using Mel 90 excimer laser

Abstract

Background: A larger optical zone for photorefractive keratectomy may improve optical quality and stability. However, there is need for limiting ablation diameter in that a larger ablation diameter requires greater ablation depth, and minimizing ablation depth may reduce adverse effects on postoperative wound healing, haze and keratoectasia. In this study, we compared the changes in clinical outcomes and the degree of regression between a 6.0 mm optical zone and 6.5 mm optical zone following PRK. Methods: The records of 95 eyes that had undergone PRK with a 6.0 OZ (n = 40) and a 6.5 OZ (n = 55) were retrospectively reviewed. We compared data including the spherical equivalent of manifest refraction (SE of MR), simulated K (Sim K), thinnest corneal thickness, change in thinnest corneal thickness (the initial value divided by corrected diopter [ΔTCT/CD]), Q value, corneal higher order aberrations (HOAs) and spherical aberration (SA) preoperation, at 3 and 6 months postoperative and at the last follow-up visit (Mean; 20.71 ± 10.52, 17.47 ± 6.57 months in the 6.0 and 6.5 OZ group, respectively). Results: There were no significant differences in the SE of MR, Sim K and UDVA between the 6.0 OZ group and the 6.5 OZ group over 1 year of follow-up after PRK, and the 6.0 OZ group required less ΔTCT/CD than the 6.5 OZ group. The 6.5 OZ group showed better results in terms of post-operative HOAs of RMS, SA and Q value. When comparing that pattern of change in Sim K, there was no significant difference between the 6.0 OZ group and the 6.5 OZ group. Conclusions: The clinical refractive outcomes and regression after PRK using Mel 90 excimer laser with a 6.0 OZ were comparable to those with a 6.5 OZ.

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

“…In our study, rf and rs were also decreased significantly. We observed that Kmax increased significantly in post-operative follow-ups, like Shin et al (24) After myopic ablation, the topography device recognizes the corneal ablation transition zone as the steepest part of the cornea and measures the Kmax value accordingly. This situation caused Kmax values to be found to be higher postoperatively.…”

A Novel Role for Corneal Pachymetry in Planning Cataract Surgery by Determining Changes in Spherical Equivalent Resulting from a Previous LASIK Treatment

“…Also, as previously described in the literature, most treatment planning systems of excimer lasers use optical zones ranging between 6 and 6.5 mm with a general trend toward larger optical zones. Tose are comparable to the optical zones used in this study [32][33][34][35]. Terefore, the principle of the CPT ratio may be applied to excimer lasers from other manufacturers than the one used in this study.…”

Myopic regression after photorefractive keratectomy: a retrospective cohort study

“…We found no significant differences in the frequency of PRK-treated eyes with optic zones of 6 or 6.5 mm between those with and without myopic regression. Shin et al found no significant differences in regression between the 6.0-mm optical zone and the 6.5-mm optical zone over one year post-PRK [ 26 ]. This is inconsistent with the findings of Mohammadi et al, who reported a significant association between an intended optical zone < 6 mm and regression [ 22 ].…”