Fine-tuning of the crosslinking procedure is producing better end results for patients.
A closer look highlighted some problems with the procedure. The epi-on procedure is more challenging than the epi-off procedure because obtaining the optimal levels of the components is more challenging with the epithelium in place. Notably, the epithelium can block both the stromal loading of the riboflavin and the UVA light but mostly affects the oxygen level.
An adequate oxygen level is paramount to the success of CXL.
“As soon as the UV light is turned on, the oxygen is consumed rapidly and an extended period is required for the oxygen level to recover,” Dr. Rocha said.
In addition, a significant biomechanical effect of CXL is dependent on oxygen. She noted with a normal oxygen level, better changes in the corneal biomechanics are seen compared to what happens when the oxygen level is low.
One approach to address this problem was attempted by adding supplemental oxygen. Dr. Rocha noted that the result was that supplemental oxygen enabled sustained aerobic CXL under high-irradiance UVA light delivery.
Phase III study
The end of the phase III multicenter registration study of epi-on CXL is near. In this randomized, sham-controlled trial, the control eyes can undergo CXL after six months. About 275 eyes with progressive keratoconus are included in patients ranging in age from 12 to 55 years. Patients are treated with transepithelial riboflavin ophthalmic solution with a 10-minute soaking time, supplemental oxygen is supplied, and an accelerated UV protocol (10 J/cm2) is used.
The primary endpoint is a 1-D difference between the treatment group and controls in the mean change in the Kmax value from baseline at the six-month time point. The results have not yet been reported.
State of the art in CXL
The best way to achieve most corneal flattening is by combining the epi-off conventional protocol with implantation of corneal implants (Intacs, Addition Technology).
The epi-off procedure is safe and the efficacy is established and approved by the FDA. The epi-on procedure provides rapid recovery, less pain, and less risk for the development of haze and infection.
“In CXL, the future is bright and the results have improved as a result of oxygen supplementation, pulsed accelerated protocols, and iontophoresis,” Dr. Rocha concluded.
Karolinne M. Rocha, MD, PhD
E: [email protected]
This article is based on Dr. Rocha's presentation at the American Academy of Ophthalmology's annual meeting. Dr. Rocha has no financial interest in any aspect of this report.