Keratoconus is a bilateral and asymmetric corneal ectasia. Cross-linking uses ultra-violate rays to enhance corneal tissue. The purpose of this study was to use in vivo confocal microscopy to quantitatively analyze microstructural changes over time, after corneal collagen cross-linking (CXL) in keratoconus patients. In this before-and-after study, a 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. Keratocytes and the present of activated keratocytes were calculated preoperatively and at 1, 3, 6, and 12 months postoperatively using confocal microscopy. One year after CXL, 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 initially (p < 0.001). During follow-up, the density of keratocytes increased significantly in all layers reaching near normal values by 12 months. The percentage of activated keratocytes showed a significant increase 1 month after cross-linking (p < 0.001) albeit this percent reduced as the corneal healing proceeded by month 12. 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 structures. Further studies are needed to assess possible changes on corneal biomechanics. The consistency in corneal endothelium numbers proves the safety of this technique.
Keywords: Cross-linking; In vivo confocal microscopy; Keratoconus; Keratocytes.