Corneal Swelling Characteristics With Hypotonic Riboflavin During Corneal Collagen Crosslinking

Abstract

Purpose: : To investigate corneal swelling using hypotonic riboflavin 0.1% during corneal collagen crosslinking (CXL).

Methods: : As part of a multi-center clinical study, 47 patients (50 eyes) underwent CXL for keratoconus (KC) or ectasia (32 and 18 eyes respectively). CXL was performed using the UVX system (Peschke Meditrade GmbH) using the technique of Seiler and colleagues. Following epithelial debridement riboflavin 0.1% plus dextran was administered every 2 minutes for 30 minutes. The corneal thickness was then checked using ultrasound pachymetry (Sonogage). For thicknesses <400µm, two drops of hypotonic riboflavin 0.1% were added every 10 seconds for 2 minutes and pachymetry rechecked; this cycle was repeated until a minimum of 400µm was reached. The cornea was then exposed to a UVA 365nm light for 30 minutes at an irradiance of 3mW/cm² with riboflavin 0.1% plus dextran administered every 2 minutes.

Results: : Thirty-nine of 50 eyes (78%) required the use of hypotonic riboflavin. Of the eyes requiring hypotonic riboflavin, the mean number of cycles of hypotonic riboflavin was 2.9 cycles (5.8 minutes). KC eyes required significantly less hypotonic riboflavin compared to ectasia eyes (mean 5.5 and 8 minutes respectively) to achieve similar thickness changes. Mean cornea swelling was 20.0µm per 2 minute cycle. For all eyes, the greatest corneal swelling (mean 41.4µm (SD 20.7)) occurred during the first cycle of hypotonic riboflavin 0.1%. No significant differences in swelling rates were seen in KC eyes compared to ectasia eyes; 17.3µm/2min (SD 17.1) and 19.6µm/2min (SD 7.4) respectively. For all eyes, neither initial corneal thickness (r²=0.004) nor endothelial cell density (r²=0.002) affected swelling rates. In KC eyes, the degree of disease severity also failed to influence swelling rates.

Conclusions: : Cornea swelling using hypotonic riboflavin may be necessary to achieve a minimum thickness of 400µm to protect the endothelium from potential UV cytotoxic effects during CXL. Ectasia eyes require more hypotonic riboflavin to achieve similar cornea swelling compared to KC eyes which may be due to the presence of the LASIK flap.

Clinical Trial: : www.clinicaltrials.gov NCT00647699 & NCT00674661

Keywords: keratoconus • refractive surgery: other technologies • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials