Cornea specialist outlines ideal candidate for cross-linking
ATLANTA – As corneal collagen cross-linking makes its way through the FDA approval process, a presenter here at SECO shared pearls for patient selection and explained the procedure’s mechanism of action.
Terry Kim, MD, chairman of the cornea department at Duke University School of Medicine, shared guidelines that he said are based on more than 20 clinical trials.
“Your ideal candidate for corneal collagen cross-linking will have a diagnosis of progression over 12 to 24 months,” he said. “He or she will have an increase of more than 1 D in terms of the steepest keratometry readings, an increase of at least 1 D in regular astigmatism and a myopic shift of at least 0.5 D.
“The patient will have the presence of central or inferior steepening, axial topography consistent with keratoconus/ectasia, the steepest manual K of at least 47 and pachymetry of at least 300 microns to 400 microns at the thinnest point,” he added.
Kim explained that with the corneal collagen cross-linking procedure, the central 7 mm to 9 mm of epithelium is removed. Riboflavin B2 in 20% Dextran is applied 5 minutes prior to the procedure and every 5 minutes during the procedure. UVA (365 nm to 370 nm) is applied for 30 minutes. Patients are treated with a bandage contact lens and topical antibiotics and steroids for 2 weeks.
Kim said that the procedure creates covalent bonds between collagen molecules.
“You’re cross-linking the cornea by this effect,” he said. “We naturally self cross-link our corneas as we get older. A 70-year-old patient is at much less risk of developing keratoconus than a 20-year-old because that cornea has already been cross-linked. It’s debated whether there’s a benefit to treating older patients.”
Kim said a debate also exists regarding removing the epithelium.
“We know that riboflavin B2 penetrates better if you take it off,” he said. “The problem is that some patients have had delayed healing because of epithelial infections or scarring.
“You can apply the riboflavin by doing stromal punctures to help it penetrate,” he continued. ”The issue is: Will you get a sustained and high enough level to have the effect of cross-linking? The other issue is changing the energy. Some use a high fluency treatment.”
Kim explained an alternative treatment.
“Some are treating patients with oral vitamin B2 and asking them to sunbathe to get the same effect,” he said. “A small German study showed some stabilization of keratoconus just doing this. We had a young basketball player a few years ago with keratoconus and we recommended this to him.”
Kim said it is important to convey to patients that keratoconus is a progressive disease.
“We know that eye rubbing has a lot to do with it,” he said. “My Down’s syndrome patients are always rubbing their eyes and they typically have advanced keratoconus. We need to try to stabilize the disease process in this condition that progresses.” – by Nancy Hemphill, ELS, FAAO
Disclosure: Kim has no relevant financial disclosures.