Collagen crosslinking helps with stabilizing progressive hyperopia post-RK
June 1, 2007
Collagen crosslinking with riboflavin (C3-R) was used to treat six eyes with progressive hyperopia after RK that had experienced further progression after intervention using laser vision correction. Retrospective analyses based on a mean follow-up of 215 days after the C3-R procedure suggests keratometric stabilization.
Beverly Hills, CA–Collagen crosslinking with riboflavin (C3-R) is showing promise as a method for arresting progressive hyperopia after RK and laser ablation, said Brian S. Boxer Wachler, MD.
Mean follow-up for the six eyes was 215 days (range, 30 to 450 days). Outcomes analyzed included change in uncorrected visual acuity, best-corrected visual acuity, sphere, cylinder, spherical equivalent, keratometry (steep, flat, average), and endothelial cell count. None of those parameters changed significantly. Looking at individual values, no eye experienced more than 1 D of change in sphere or refractive cylinder or significant worsening of corneal topography, and a few exhibited keratometric steepening.
"However, based on these preliminary results, we are hopeful that stabilization is occurring and that this might be a nice treatment to offer patients who are suffering from progressive hyperopia after RK," he added.
Explaining the rationale, Dr. Boxer Wachler said post-RK corneas are often- although not always-unstable and that C3-R strengthens the cornea by causing fibril thickening and crosslinking.
"Pioneering work from Theo Seiler, MD, PhD, established that this technique could safely stabilize keratoconus, essentially by increasing biomechanical stiffness and making the cornea stronger," Dr. Boxer Wachler said.
"Its efficacy and safety as measured by lack of adverse changes in corneal and lens transparency, IOP, and endothelial cell count has subsequently been confirmed by other investigators," he said.
"We've been interested in evaluating the crosslinking procedure for stabilizing keratometry in corneas with a variety of pathologies, including progressive hyperopia post-RK. These latter eyes often go on to treatment with hyperopic LASIK or PRK," he added. "However, if the cornea is inherently unstable, the improvement gained with those procedures is likely to be only a temporary effect."
The treatment protocol was similar to that described by Wollensak and Seiler in their original 2003 paper in the American Journal of Ophthalmology with the exception that Dr. Boxer Wachler does not remove the epithelium. The central 7 mm of the cornea is exposed to 370-nm ultraviolet-A irradiation (5.4 J/cm2 ) for 30 minutes with application of the photosensitizing solution containing 0.1% riboflavin-5-phosphate and dextran prior to and every 3 minutes during the light treat- ment, he said.
The five patients analyzed had a mean age of 51 years and comprised two males and three females.
Individual results showed that sphere increased slightly in three eyes and decreased slightly in the other three; mean preoperative sphere was 2.04 D and was unchanged postoperatively.
Cylinder was unchanged in two eyes, increased slightly in two eyes, and decreased slightly in two eyes. Mean preoperative sphere was –1.88 D and decreased by an average of 0.04 D.
The average K value was 40.01 D preoperatively and was essentially unchanged at 39.98 D at the last postoperative visit, he said.
"The changes in keratometry observed in some of these patients are consistent with the idea that if RK weakens and flattens the cornea, this procedure may be tightening the incisions and thereby causing corneal steepening," Dr. Boxer Wachler said.
Mean endothelial cell count increased from 2,447 cells/mm2 to 2,711 cells/mm2 .
"The latter change likely reflects variability of the measurement rather than any effect of the procedure," Dr. Boxer Wachler said.