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

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 mum (CXL-Plus; p < 0.0001) and changed from 0.71 +/- 0.28 to 0.73 +/- 0.36 mum (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.