|Nov 2, 2011
By: Lynda Charters
Bristol, United Kingdom—Transepithelial crosslinking is effective for increasing the best-corrected visual acuity (BCVA) and reducing the corneal curvature in patients with progressive keratoconus, but it is not as effective as results reported previously. Epithelial debridement might not be necessary to the success of the procedure.
“Crosslinking procedures performed with unstable riboflavin and ultraviolet radiation (UV-A) are used in ophthalmology to create new bonds between collagen fibers to strengthen the cornea,” said Tahmina Islam, FRCS, MRCOphth, Bristol Eye Hospital, Bristol, United Kingdom. “The standard technique includes debridement of the corneal epithelium, but this can be complicated by infections, slow healing, subepithelial haze, and discomfort.”
Because riboflavin does not readily penetrate the ocular tissues, substances that enhance riboflavin’s ability to penetrate the eye were evaluated. In this study gentamicin, anesthetics, and ethylendiaminetetraacetic acid (EDTA) have been used to enhance the epithelial permeability as well as benzalkonium chloride and surfactants. Dr. Islam evaluated the feasibility of using these substances with a transepithelial approach.
She and co-author Antonio Leccisotti, MD, PhD, the first author on this study and visiting professor at the School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, and director of the Ophthalmic Department, Casa di Cura Rugani, Siena, Italy, designed a prospective, consecutive, single-masked, paired-eye study that included 51 patients with progressive keratoconus. The patients ranged in age from 18 to 40 years.
The study protocol included 3 hours of eye drop instillation before the crosslinking procedure. Specifically, gentamicin, benzalkonium chloride, and EDTA were instilled for 3 hours, then oxybuprocaine for 30 minutes. Riboflavin 0.1% in 20% dextran T500 and oxybuprocaine then were instilled for 30 minutes. UV-A irradiation was applied to the central 7.5 mm of the cornea for 30 minutes, while riboflavin was instilled every 5 minutes, Dr. Islam explained.
“The results were promising and showed improvements in corneal curvature 1 year after the treatment,” Dr. Islam said. The authors recently published their results (Leccisotti A, Islam T. Transepithelial corneal collagen cross-linking in keratoconus. J Refract Surg. 2010;26:942-948).
The investigators found that the mean best spectacle-corrected visual acuity improved by 0.036 logarithm of the minimum angle of resolution (logMAR) after crosslinking and worsened by 0.039 logMAR in the controls (p < 0.05). The safety index was 1.05 after crosslinking and 0.96 in the control group. The mean spherical equivalent decreased by 0.35 D (less myopic) after crosslinking and increased by 0.83 D in the controls (p < 0.05). The mean apex curvature increased by 0.51 D after crosslinking and by 1.61 D in the controls, a difference that was not significant. The mean average simK decreased by 0.10 D after crosslinking and increased by 0.88 D in the controls (p < 0.05). The mean index of surface variance worsened by 0.9 after crosslinking and by 5.3 D in the controls (p < 0.05). Finally, the mean endothelial cell density remained unchanged.
The cases previously reported in the literature using this crosslinking technique had reductions in spherical equivalent, flattening of the cornea, and improvements in BCVA, she said. However, the current cases, according to Dr. Islam, did not have results that were as good as those previously reported.
“However, the results, while not quite as comparable, were still good,” she said.
The investigators concluded that epithelial debridement is not fundamental to the treatment.
“Despite this, the procedure still achieved improvements in BCVA, a reasonable decrease in the mean corneal curvature, and maintained the safety of the endothelium,” Dr. Islam said. “Most importantly, however, we can reduce complications such as the development of haze and infection and improve comfort for all patients.”