Keratoconus: cracking the corneal code

Denver-During the American Academy of Optometry's Academy 2014, leading researchers and clinicians detailed the latest knowledge regarding the origins of and treatments for keratoconus.

Jan Bergmanson, OD, PhD, professor, University of Houston College of Optometry, said that histopathological research conducted at the Texas Eye Research and Technology Center has shown that the pathological changes of keratoconus have an anterior focus, involving both the epithelial and anterior stromal tissue. In particular, this research has demonstrated that corneal stromal lamellae break up into smaller pieces. When this lamellar splitting co-occurs with corneal thinning, as in keratoconus and post-refractive surgery, says Dr. Bergmanson, ectasia develops.

When do you diagnose keratoconus?

Conversely, the “slippage” theory posits that the lamellae slide over each other, creating a thinner cornea over the cone. To examine this theory, Dr. Bergmanson and colleagues essentially counted the lamellae in the entire cornea, which had never been done before.

“We found that there were more lamellae in the keratoconus than normal corneas. We wondered what we had done wrong-this could not be true.” But ultimately, says Dr. Bergmanson, researchers realized that patients who undergo refractive surgery already have at least the beginnings of lamellar splitting. “So we concluded that for ectasias to occur, you need lamellar splitting. But you also need thinning of the cornea.” He likened lamellar splitting to a rope that unravels over years. Because keratoconus is a pan-corneal phenomenon, he adds, “Scleral contact lenses make a great deal of clinical sense.”

Dr. Bergmanson and colleagues also have observed that over time, some transplant patients seem to develop recurrent keratoconus. In other words, “Was your patient so unlucky that he got someone else's keratoconus?”

Previously, he says, it was unclear whether this disease emanated from the host or donor tissue. But in the case of a musician whose keratoconus returned 25 years after he underwent bilateral penetratingkeratoplasty (PKP), said Dr. Bergmanson, the odds of contracting keratoconus from both donors used were one in 4 million. “Today, we call this complication recurrent keratoconus. If the pathology is never completely surgically removed, it may find its way to the donor tissue." Accordingly, he says, “Recurrence is really reemergence,” a risk of which optometrists should inform transplant patients.

Regarding the therapeutic armamentarium, Optometry Times Editorial Advisory Board member William Tullo, OD, predicted that with 27 clinical studies underway, some form of corneal collagen cross-linking will earn FDA approval in 2015.

While preferred orientations for lamellae allow the cornea to maintain transparency, says Dr. Tullo, “We see significant differences in the different regions of the cornea,” anterior versus posterior, and central versus peripheral. Additionally, “As patients get older, their Young's modulus-which is a very good direct measure of corneal rigidity-increases. We don't know exactly what is happening in the cornea. But we see this stabilization with age, and that's why we see less progression with time."

He and his colleagues discovered-accidentally-that applying riboflavin, UV-A and oxygen stimulates cross-linking, which strengthens the cornea. "We're doing the exact opposite of what we do in macular degeneration-we're purposely putting free radicals on the cornea to induce these covalent bonds."

Regarding the procedure's efficacy, he said in nearly 700 studies, 96 percent of treated eyes achieved topographic stability, and an average flattening of 1.7 D. As for safety, he says the procedure exposes patients' corneas to less UV than they would get in 15 minutes under Florida sunshine.