AUG 31, 2016
Investigators have shown that epithelium-on corneal collagen crosslinking (CXL) using tetracaine can result in significant corneal flattening and improved vision in patients with advanced kerataconus.
While more evidence is needed to truly show the effectiveness of epi-on versus epi-off CXL, this small study offers some evidence that an effective epi-on protocol may exist. The authors used tetracaine 1.0% to initiate chemical disruption of the epithelial tight junctions, and a hypotonic riboflavin solution was used without dextran to increase the permeability of the corneal epithelium.
It was a prospective study that included 21 patients with bilateral keratoconus. Only the patient’s worse eye was treated. During the riboflavin imbibition period, patients were allowed to blink normally. Tetracaine 1.0% without BAC was applied every minute for 15 minutes. Subsequently, hypotonic riboflavin 0.5% solution without dextran (China Resources Double-Crane Pharmaceutical Co. Ltd.) was applied every minute for 30 minutes. UVA with irradiance of 3mW/cm2 was applied over the cornea for 30 minutes.
At 1-year postop, patients experienced a significant improvement in both uncorrected and corrected distance visual acuity compared with baseline (both, P ≤0.009). Kmax values decreased by 1.63 D in treated eyes compared with untreated fellow eyes (P<0.001).
Additionally, investigators noted a significant decrease in anterior elevation but not in posterior elevation, suggesting that flattening occurred mainly in the anterior cornea. Cross-linking with this algorithm did not affect central corneal thickness or posterior corneal curvature.
The study is limited by its small sample, and investigators did not measure the demarcation line and degree of discomfort after the treatment. Finally, an argument could be made that selecting the worse eye selects the more burnt out or stable eye, which could skew results. While more research is required, this protocol achieved sufficient topographic flattening and the risk for corneal haze or scar formation was minimized.