Purpose: To study the corneal flattening effect of cross-linking (CXL) overtime and to look for a potential association with preoperative topographic variables and the central depth of demarcation line (DDL).
Methods: 201 eyes of 146 patients (mean age of 31.2 ± 7.3 years) with progressive keratoconus who underwent CXL between June 2007 and December 2012 were enrolled in this retrospective study. Follow-up visits were performed at different time intervals for at least 5 years. Preoperative parameters and depth of demarcation line were collected from LaserVision ophthalmology center in Lebanon. Corneal flattening was defined by a change in postoperative Kmax (ΔKmax) greater than 1.00 D.
Results: ΔKmax increased from 50.25% to 61.69%, from first to last follow-up visits. The only factor significantly correlated to ΔKmax during all follow-up visits was preoperative maximum keratometry (Kmax) especially when greater than 50.00 D (OR, 1.92; 95% CI, 1.10-3.34). All eyes showed a corneal demarcation line (mean central depth (DDL): 217.11 ± 26.54 μm), with no statistically significant correlation between DDL and ΔKmax.
Conclusion: CXL effect on cornea can be cumulative overtime and delayed flattening occurs in some cases. ΔKmax is positively correlated with preoperative Kmax and no association was found between ΔKmax and DDL. Therefore, DDL may not be a valid measure for the efficacy of CXL.
Keywords: Corneal dystrophies; corneal degenerations; diseases of the ocular surface; examination techniques: pachimetry; ocular surface surgery.