Biomechanical parameters of the cornea after collagen crosslinking measured by waveform analysis

PURPOSE: To compare 2 corneal biomechanical parameters--corneal hysteresis (CH) and corneal resistance factor (CRF)--before and after collagen crosslinking (CXL) for keratoconus. SETTING: Eye Research Center of Mashhad University of Medical Sciences, Khatam-al-Anbia Eye Hospital, Mashhad, and Department of Ophthalmology, Baqiyatallah University of Medical Science, Tehran, Iran. DESIGN: Case series study. METHODS: Topical riboflavin was applied to the deepithelialized cornea every 3 minutes for 30 minutes and every 5 minutes during ultraviolet-A irradiation of the cornea. Corneal hysteresis and CRF were measured by biomechanical waveform analysis (Ocular Response Analyzer) before and 6 months after CXL. The values were compared using the paired Student t test. RESULTS: The study comprised 51 patients (56 eyes). The mean age of the patients was 23.27 years ± 6.3 (SD). Before CXL, the mean CH was 7.9 ± 1.5 mm Hg and the mean CRF was 7.3 ± 1.4 mm Hg. Six months after CXL, the mean values were 8.20 ± 1.5 mm Hg and 7.59 ± 1.5 mm Hg, respectively. The changes in CH and CRF were not statistically significant (P>.05). The changes in central corneal thickness and Goldmann-correlated intraocular pressure (IOP) between preoperatively and postoperatively were not statistically significant, although the change in corneal-compensated IOP was (P<.05). CONCLUSION: Although previous in vitro studies found a change in corneal rigidity, this study found no significant change in CH or CHF measured by biomechanical waveform analysis.