Additive Effect of Repeated Corneal Collagen Cross-linking in Keratoconus

PURPOSE: To report the long-term clinical outcome in a patient diagnosed as having bilateral progressive keratoconus who received a single corneal collagen cross-linking (CXL) treatment in the right eye and repeated CXL in the left eye. METHODS: Observational case report. Topographical changes were assessed by high-resolution Scheimpflug imaging. The right eye underwent a standard epithelium-off CXL procedure in February 2008, followed by the left eye 4 weeks later. In 2012, the left eye was treated with CXL for a second time. Irradiation was performed in all cases at a fluence of 5.4 J/cm(2). Energy settings were 30 minutes @ 3 mW/cm(2) for the CXL procedures performed in 2008, and 10 minutes @ 9 mW/cm(2) for the second CXL procedure of the left eye that was performed in 2012. RESULTS: The right eye that underwent a single CXL procedure showed a flattening of keratometry values between 2008 and 2012, followed by stabilization. The left eye showed a similar flattening effect between 2008 and 2012, followed by another flattening effect after the second CXL procedure and accompanied by a distinct increase in corrected distance visual acuity. CONCLUSIONS: Following repeated CXL, the corneal stroma and endothelium remained inconspicuous, and postoperative haze and visibility of the stromal demarcation line was similar to what is usually observed after a single CXL procedure. Whether the additive flattening effect of the anterior surface observed in this single case goes along with an additive increase in biomechanical stiffness remains to be seen.