Clinical and corneal biomechanical changes after collagen cross-linking with riboflavin and UV irradiation in patients with progressive keratoconus: results after 2 years of follow-up.

PURPOSE To assess the biomechanical and keratometric effects and the safety of treatment of progressive keratoconus with UV-riboflavin collagen cross-linking (CXL). METHODS This is a prospective clinical controlled study. Fourteen eyes of 14 patients with progressive keratoconus were treated with CXL after corneal deepithelization. Patients were assessed preoperatively, at week 1 and at months 1, 3, 6, 9, 12, and 24 after treatment. We measured uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA) (logarithm of the minimum angle of resolution), refraction, biomicroscopy and fundus examination, intraocular pressure, axial length, endothelial cell density, corneal topography, minimal corneal thickness, macular optical coherence tomography, and corneal biomechanics with the ocular response analyzer. RESULTS Comparing the preoperative results with 24-month postoperative results, we observed significant improvement in BCVA (0.21 ± 0.1 to 0.14 ± 0.1, P = 0.002) and stability in UCVA (0.62 ± 0.5 and 0.81 ± 0.49, P = 0.475). We observed a significant decrease in steepest-meridian keratometry (diopters) (53.9 ± 5.9 to 51.5 ± 5.4, P = 0.001) and in mean cylinder (diopters) (10.2 ± 4.1 to 8.1 ± 3.4, P = 0.001). Significant elongation of the eyes was observed, from 24.39 ± 1.7 mm to 24.71 ± 1.9 mm (P = 0.007). No significant change was observed in mean simulated keratometry, minimal corneal thickness, endothelial cell density, corneal hysteresis, and corneal resistance factor or foveal thickness. CONCLUSIONS Two years after CXL, the observation of stable UCVA, improved BCVA, and reduced keratometry suggests stabilization in progression of keratoconus. Unchanged corneal thickness, endothelial cell density, and foveal thickness suggest the long-term safety of this procedure. The observed increase in axial length and stability in corneal biomechanical parameters measured with the ocular response analyzer require further study for verification and explanation.