Visual and refractive effects of collagen cross-linking in keratoconus

PURPOSE: Evaluation of visual and refractive effects of collagen cross-linking (CXL) in progressive keratoconus (KCN).
METHODS: A total of 95 eyes of 77 patients were retrospectively analyzed. The changes in uncorrected and corrected distance visual acuities (UDVA and CDVA, respectively); spherical or cylindrical refraction and spherical equivalent of refractive error (SPH, CYL, and SE, respectively); central corneal thickness (CCT); and mean keratometry values (K) in the Scheimpflug corneal tomography (Pentacam, Oculus®, Germany) were evaluated at the 1st, 3rd, and 6th post-operative months and the past visit, as compared to pre-operative values.
RESULTS: During follow-up, there was a progressive improvement in the mean UDVA and CDVA. Significant improvement was seen in CDVA at the 3rd month (from 0.51±0.23 to 0.59±0.22), in UDVA at the 6th month (from 0.34±0.24 to 0.44±0.25), and in SPH and SE values at the last control (from −2.75±3.50D to −1.92±2.52D for SPH; from −3.51±4.45D to −3.07±3.05D for SE). The mean CCT decreased in the post-operative 1st month and gradually increased in the 3rd and 6th months (from 466.87±63.94 μm to 449.76±50.09 μm, 443.92±42.44 μm, and 454.30±46.86 μm for 1st, 3rd, and 6th months, respectively); almost returned to pre-operative values. There was no significant change in mean CYL and K values throughout the follow-up (from −2.40±2.11D to −2.45±1.77D for CYL; from 46.89±3.66D to 47.35±5.04D for K).
CONCLUSION: CXL seems to not only slow down the progression of KCN but also improve the visual acuity, which may be a result of ultrastructural changes that occur in the corneal stroma postoperatively, rather than a simple corneal flattening effect.