Changes in higher order aberrations after central corneal regularization - a comparative two-year analysis of a semi-automated topography-guided photorefractive keratectomy combined with corneal cross-linking

Abstract

Background: The optical quality in progressive keratoconus deteriorates due to ectasia and distortion of the corneal shape and optics. While corneal cross-linking (CXL) aims at stopping disease progression, "CXL-Plus" combines CXL with excimer laser ablation to improve visual function. Central Corneal Regularization (CCR) represents a therapeutic excimer laser modality specifically designed to smoothen the ectatic corneal shape and to reduce higher order aberrations (HOA). We set out to compare CXL-Plus, consisting of CXL combined with CCR, with CXL by itself for patients with progressive keratoconus. Methods: Retrospective 2-year matched group analysis of patients who either underwent CXL-Plus (n = 28) or CXL as a sole procedure (n = 28) for progressive keratoconus. Main outcome parameters were HOA, visual function and tomographic results 12 and 24 months postoperatively. Results: After 12 months, the total HOA root mean square wavefront error was reduced from 0.79 ± 0.30 to 0.40 ± 0.19 μm (CXL-Plus; p < 0.0001) and changed from 0.71 ± 0.28 to 0.73 ± 0.36 μm (CXL; p = 0.814). Uncorrected distance visual acuity improved from 0.70 ± 0.35 to 0.36 ± 0.29 logMAR (CXL-Plus; p = 0.0002) and from 0.65 ± 0.39 to 0.46 ± 0.37 logMAR (CXL; p = 0.067), translating to gains of three or more lines in 50% (CXL-Plus) and 36% (CXL) of patients. The steepest keratometry value (Kmax) regressed by 5.84 D (CXL-Plus; p < 0.0001) and 0.66 D (CXL; p = 0.752). For none of the investigated parameters a statistically significant change could be shown between 12 and 24 months. Conclusions: CXL-Plus in the form of a CCR reduces HOA and Kmax more effectively than CXL as a sole procedure.

Evaluation of Corneal Aberration Alterations After Accelerated Transepithelial Corneal Crosslinking

“…However, the failure of these refractive corrections in KCN patients was explained by the increased HOAs 17 . The normal value of total HOAs in the healthy population is around 0.30µm, however, several studies detected higher HOAs in KCN patients ranging between 0.71-10.94µm 12, 18,19 . The mean of preoperative HOAs was 1.62±0.57 µm in our study.…”

Long Term Evaluation of Posterior Corneal Surface Parameters after Accelerated Corneal Crosslinking with a Comparison with Uncross-Linked Keratoconic Eyes

“…Therefore, evaluation of both anterior and posterior corneal surface HOAs allows increased understanding of the optical quality of keratoconic eyes [20]. In studies by Hassan and Iselin et al, aberrations of the posterior corneal surface did not change at 7 and 24 months after CCL [6,21]. In the present study, higher-order aberrations of the posterior corneal surface did not signi cantly change in a post-CCL follow-up period of 36 months similar to the study by Iselin et al Greenstein et al compared HOA changes at 1 year post-CCL between crosslinked and control ectatic eyes, and concluded that there was a mean decrease in posterior corneal HOAs in the treatment group while there was a mean increase in the control group [22].…”

A Clinical Decision Tree to Support Keratoconus Patients Considering Corneal Cross-Linking Combined with Refractive Treatment

“…Patient selection criteria are described in detail elsewhere [5]. In summary, we analyzed patients treated for progressive keratoconus using a uniform CXL protocol without any other diseases affecting visual function.…”

“…In a recent matched group analysis, we were able to show that CXL plus reduces higher-order aberrations and the steepest radius of anterior curvature (K max ) more effectively than CXL only [5]. The matching of datasets balanced the distribution of covariates, making the two groups differ only randomly with respect to all covariates and therefore allowing a clear statement regarding the efficiency of CXL plus.…”