Corneal Collagen Crosslinking(CXL) is a minimally invasive surgical procedure to slow or halt keratoconus or other corneal ectasia. There are two categories of Epi-On and Epi-Off. Epi-Off is further divided into two different protocols for delivery-the Dresden Protocol and Accelerated CXL. “Epi” refers to the epithelium or top layer of the cornea. In Epi-Off the epithelium is removed prior to the procedure. In Epi-On the epithelium is left in place while the procedure is performed.
The Dresden protocol for Epi-Off has been FDA approved since 2016. This protocol is considered by experts to be relatively reliable and have fairly good outcomes. The Dresden Protocol involves “painting” a solution of dextran and riboflavin onto the cornea, which breaks down the bonds of the cornea. Then a UV light is used to re-attach the bonds. The bonds are then stronger than they were originally. The downside of this procedure is that the solution applied to the cornea to break the bonds can dehydrate the cornea, causing scarring, melting, infection, and/or delayed wound healing. The vision can fluctuate afterward for 3-6 months.
Accelerated Collagen Crosslinking (CXL)
Accelerated CXL offers a shorter exposure to the UV light which may reduce the risk of complications and speed recovery time
Some keratoconus patients may have corneas which are too thin for Epi-Off CXL. Epi-On can accommodate some of these patients. This procedure has faster recovery, lower risk of side effects and offers more stable vision than Epi-Off. The biggest downside of this protocol is that is may be less effective in strengthening the cornea because the riboflavin my not penetrate the cornea as well through the intact epithelium. Epi-On is currently in phase III clinical trials, which should be complete by June 2020.
Other Cornea Strengthening Investigations:
I-CXL uses low volt electrical current to attempt to increase the penetration of riboflavin deeper into the cornea.
PiXl customizes where the UV light is applied to attempt to normalize the corneal shape while strengthening it.
Other Refractive CXL
Athens Protocol combines CXL and PRK (photo refractive keratectomy). This method combines saline with the riboflavin instead of dextran which causes less dehydration to the cornea. PRK is a laser procedure which re-shapes the cornea to attempt to normalize the shape.