In the 15 years since corneal cross-linking was introduced, unexpected results and complications have occurred only rarely, said Farhad Hafezi, MD PhD, whether used for keratoconus, corneal ectasia, edema, melting or infectious keratitis.
However, when they do occur, it’s usually because the limits of the procedure were not respected, Dr. Hafezi said at the 2014 meeting of the European Society of Cataract and Refractive Surgeons.
The endothelial damage threshold level was determined at 0.36 mW/cm2. When applied in corneas with a stromal thickness of 400 µm and more, the current fluence settings allow for safe CXL because the initial energy is subsequently attenuated in deeper layers. If overall fluence and minimal thickness are respected, the endothelium should not decompensate.
He said that the few reports published on endothelial decompensation involved dextrane in the riboflavin solution, which is known to induce stromal thinning, while others used handheld ultrasound pachymetry as the only measure to determine corneal thickness.
While transient haze related to UV light is standard, if it persists beyond three or four months it may become permanent and often occurs concomitant with a massive reduction in Kmax readings of up to 10D. Dr. Hafezi said such reactions are rare and were observed in about one in 200 cases. He also noted no case of stem cell decompensation has occurred in 15 years.
“There have been a number of case reports on infectious keratitis after CXL, it usually happens when there’s a mishandling of the open surface or improper use of medication,” Dr. Hafezi said.
In cases of infection with subsequent melting, it was also reported that the patient abused topical NSAIDs on the open corneal surface. NSAIDs may upregulate matrix metalloproteinases and other collagenases, and induce corneal melting. As a result, he doesn’t prescribe NSAIDS for pain. Instead, he uses a bandage contact lens for the first night only.
In other presentations on CXL here in London, the consensus is that, as of today, epi-on corneal collagen cross-linking is still the preferred method. The experimental work done with epi-on procedures is promising and exciting anecdotal evidence was presented, but there is not enough evidence to support its use currently.