PURPOSE

To use in vivo confocal microscopy (IVCM) to quantitatively analyze microstructural changes over time, after corneal collagen cross-linking for keratoconus.

DESIGN

Prospective cohort study.

PARTICIPANTS

A total of 38 eyes of 38 patients undergoing collagen cross-linking for keratoconus.

METHODS

Prospective, clinical cohort study of corneal collagen cross-linking in progressive keratoconus. Laser scanning IVCM performed preoperatively and at 1, 3, 6, and 12 months postoperatively.

MAIN OUTCOME MEASURES

Density of corneal sub-basal nerves, anterior and posterior keratocytes, and corneal endothelium.

RESULTS

Compared with baseline values, the mean sub-basal nerve density decreased significantly at 1, 3, and 6 months postoperatively (P < 0.01); however, this returned to preoperative values at 12 months (P = 0.57). One month postoperatively, there was complete absence of keratocyte nuclei in 86% of corneas. Anterior stromal edema with hyper-reflective cytoplasm and extracellular lacunae in a honeycomb-like appearance was observed and persisted at 3 months postoperatively. Scattered, presumed fragmented keratocyte nuclei, were observed at 1 and 3 months, but by 6 months, keratocyte repopulation of the anterior stroma was apparent. Quantitative analysis confirmed a significant decrease in the mean anterior keratocyte density 1, 3, and 6 months postoperatively (P ≤ 0.01) with return to baseline values at 12 months postoperatively (P = 0.57). The demarcation between treated and untreated corneal stroma appeared as a region where normal keratocytes transitioned into elongated, hyper-reflective, needle-like structures and then into large hyper-reflective stromal bands. There was no significant change in posterior keratocyte density or endothelial density at any postoperative time point.

CONCLUSIONS

This prospective IVCM study revealed complete loss of the sub-basal nerve plexus and loss of anterior stromal keratocytes in the early postoperative period, with complete regeneration of the sub-basal nerve plexus and keratocyte repopulation by 12 months postoperatively. The posterior stroma and corneal endothelium were unaffected.