Keratoconus is a bilateral and asymmetric corneal ectasia. Progressive corneal thinning leads to deteriorated visual acuity. Cross-linking uses ultra-violate rays to induce covalent bonds between collagen fibers and enhancement of corneal tissue. The purpose of this study was to use in vivo confocal microscopy (IVCM) to quantitatively analyze microstructural changes over time, after corneal collagen crosslinking in keratoconus patients.

In this before-and-after study, total of 45 keratoconic eyes were selected for cross-linking among patients referred to Al-Zahra ophthalmology clinic during 2013- 2014. All patients underwent complete ophthalmologic examinations including best corrected and uncorrected visual acuity and refractive errors. Keratocytes and the presence of activated keratocytes were calculated preoperatively and at 1, 3, 6, and 12 months postoperatively using confocal microscopy. All collected data were analyzed statistically using ANOVA test and Bonferroni correction.

One year after collagen cross-linking best corrected and best uncorrected visual acuity was increased significantly (p<0.001). Spherical equivalent and spherical refractive errors reduced significantly (p<0.001). The reduction in density of anterior and mid stromal keratocytes was significant (p<0.001). The percentage of activated keratocytes showed a significant increase one month after cross linking (p<0.001) albeit this percent reduced as the corneal healing proceeded. The endothelial cells showed no significant reduction during the follow up.

Collagen cross-linking induced significant reduction in keratocyte density. The percent of activated keratocytes increased significantly after cross-linking which showed reduction with improvement of corneal healing. After collagen cross-linking, hyper reflective structures were observed consistent with the stromal collagen