Photorefractive keratectomy in mild to moderate keratoconus: Outcomes in over 40-year-old patients

Abstract

Background:Keratoconus is a contraindication for photorefractive keratectomy (PRK). In the recent decade, some efforts have been made to perform PRK in patients with keratoconus whose corneas are stable naturally or by doing corneal collagen crosslinking. These studies have suggested residual central corneal thickness (CCT) ≥450 μm.Aims:The aim was to evaluate the long-term outcomes of PRK in patients with mild to moderate keratoconus in patients older than 40 with residual CCT ≥ 400 μm.Settings and Design:This prospective study was conducted in our Cornea Research Center, Mashhad, Iran.Materials and Methods:Patients over 40 years old, with a grade I/II keratoconus without progression in the last 2 years were recruited. Patients with a predicted postoperative CCT < 400 μm were excluded. PRK with tissue saving protocol was performed with Tecnolas 217 Z. Mitomycin-C was applied after ablation. The final endpoints were refraction parameters the last follow-up visit (mean: 35 months). Paired t-test and Chi-square were used for analysis.Results:A total of 38 eyes of 21 patients were studied; 20 eyes (52.6%) with a grade I and 18 eyes (47.4%) with grade II keratoconus. The mean uncorrected visual acuity, best corrected visual acuity (BCVA), spherical equivalent, cylindrical power and keratometric readings were significantly improved at the final endpoint compared to preoperation measurements (P < 0.001). Two eyes (5%) lost two lines of BCVA at the final visit. No case of ectasia occurred during the follow-up course.Conclusions:PRK did not induce keratoconus progression in patients older than 40 with a grade I/II keratoconus. Residual CCT ≥ 450 μm seems to be sufficient to prevent the ectasia.

Outcomes of photorefractive keratectomy in patients with atypical topography

“…Among the remaining 19 eyes, corrected distance visual acuity was improved in 16 (84.3%), declined in two (10.5%), and unchanged in one (5.2%) eyes. Also Khakshoor et al reported similar results in patients older than 40 years with grade I or II keratoconus ( 19 ). In the mentioned study, variables such as keratometric readings, uncorrected visual acuity, best corrected visual acuity, spherical equivalent, and cylindrical power were evaluated.…”

“…Our findings are compatible with similar studies. Some studies on the efficacy and safety of PRK in keratoconus have reported a low risk for progression of keratoconus ( 6 , 19 ). Atypical indices, including inferior steepening, high keratometery, low pachymetery, high anterior and posterior elevation and high SRAX had no influence on the rate of keratoconus in this study.…”

Surgical Options for the Refractive Correction of Keratoconus: Myth or Reality

“…Both studies concluded that PRK in eyes with suspected keratoconus, carefully selected, might be a safe and effective procedure for reducing or eliminating myopia and/or astigmatism. Two studies evaluated the PRK in patients with mild to moderate stable keratoconus [ 20 , 21 ]. Chelala et al [ 20 ] in a five-year follow-up study analysed the visual outcomes of PRK in 119 eyes with grade 1-2 keratoconus according to Amsler-Krumeich classification.…”

“…Only two eyes (1.7%) showed progression of the disease at 5 years of follow-up. In the Khakshoor et al [ 21 ] study, 38 stable keratoconus (grades I-II, Amsler-Krumeich) of 21 patients over 40 years old were recruited. At the last follow-up visit, in 22 eyes, the UDVA was 20/20 and in 8 eyes 20/25.…”

“…In Bilgihan et al's study [ 18 ], the residual stroma was thicker than 400 μ m in all eyes at the completion of stromal ablation. Kasparova and Kasparov [ 22 ] recommended a minimal corneal thickness > 500 μ m and a residual corneal thickness ≥ 450 μ m. Koller et al [ 23 ], Chelala et al [ 20 ], and Guedj et al [ 19 ], in their respective studies, also kept a minimum residual corneal thickness of ≥450 μ m. Khakshoor et al [ 21 ] in a group of keratoconic patients with a mean age of 44 years old reported safe outcomes maintaining a residual corneal thickness ≥ 400 μ m. The authors suggested that, as the cornea is much more stiffness in older patients due to natural collagen cross-linking, the residual corneal thickness can be thinner.…”