The Effect of Corneal Collagen Cross-Linking on Higher Order Aberrations in Keratoconus

Abstract

Purpose: To assess the changes in ocular high order aberrations after collagen cross linking for keratoconus. Patients and Methods: This study included 30 eyes with confirmed KCN. Baseline evaluation focused on: UDVA and BSCVA using logMAR notation, MRSE, corneal topography using Orbscan IIZ and wave-front aberrometry using Zywave II. CXL was performed per ‘Dresden protocol’ through a 30-minutes exposure to 370 nm UVA with an irradiance of 3 mW/cm 2. Patients had comprehensive ophthalmic evaluation after 6 months with special attention to: UDVA, BSCVA, MRSE, corneal topography and wave-front aberrometry changes.  Results: The mean age was 25.5±5.84 (20:31) years. After 6 months, there was a significant decrease in corneal thickness from 493.2± 24.17µ to 486.7±24.26µ (P<0.05) and a significant decrease in K max from 47.4±1.17D to 46.1±1.17D (P<0.05). BSCVA improved from preoperative value (0.00:0.5 logMAR (median 0.3)) to 6 months’ value (0.1:1.00 logMAR (median 0.2) (P <0.05). Preoperative MRSE was -7.25: -0.5D (median -2.85D) and at 6 months was -6.25: -0.5D (median - 2.125D) (P<0.05). A significant correlation was found at 6 months between changes in both BSCVA and: K max (P<0.001), corneal thickness (P<0.05), vertical coma (P<0.001) and trefoil (P<0.001).  Conclusions: Improvement in HOA was detected after CXL for KCN. The changes in total, vertical coma and vertical trefoil aberrations were significantly correlated with postoperative improvement in BSCVA. Thus, improvement in HOA profile after CXL is one of the explanations of improvement in visual function after CXL in KCN.