Alternative to Corneal Transplant for Keratoconus Promising

Marcia Frellick

October 25, 2016

CHICAGO — For people with keratoconus, the minimally invasive transplantation of just the second layer of the cornea — the Bowman layer — can help delay or prevent full corneal transplantation or other high-risk procedures, new results from a long-term study show.

The 5-year findings — which build on 3-year data — were presented here at the American Academy of Ophthalmology 2016 Annual Meeting by investigator Jack Parker, MD, from the University of Alabama at Birmingham Callahan Eye Hospital.

Keratoconus is a degenerative disease that causes the cornea to become thin and cone-shaped. It can first appear in childhood or adolescence, and can lead to severe visual impairment, including myopia, astigmatism, and blindness. The prevalence is about 1 in 2000.

Because the cornea becomes cone-shaped, patients cannot wear contact lenses for extended periods, and glasses can lose their effectiveness. Other treatment options include corneal collagen cross-linking with laser, which involves the use of eye drops to strengthen collagen fibers, and deep anterior lamellar keratoplasty, which involves implantation of the front and middle layers of the cornea.

Some patients will need a full corneal transplant, but adverse effects can be associated with wound healing and persistent astigmatism.

In this study, all participants had 20/400 vision with glasses before transplantation and could not wear contacts for extended periods of time. None were eligible for cross-linking because their corneas were too steep and thin.

At 5-year follow-up, Bowman layer transplantation improved vision to 20/200 and stabilized disease in 90% of 22 eyes with advanced keratoconus. None of the 19 patients studied experienced any complications after surgery, and all could wear contact lenses for extended periods.

An advantage of Bowman layer transplantation is that it does not involve an incision, Dr Parker explained. Donor tissue is inserted into the middle layer of the recipient eye through a tiny tube, which strengthens and flattens the cornea, making it easier to wear contact lenses. In addition, the Bowman layer is acellular, which reduces the risk for rejection.

Technique Only Suited for Niche Population, Experts Caution

The number of patients for which Bowman layer transplantation is uniquely the best option at this time is relatively small.

Although the technique has merit, "the number of patients for which Bowman layer transplantation is uniquely the best option at this time is relatively small," said Stephen McLeod, MD, professor and chair of the Department of Ophthalmology at the University of California, San Francisco.

"The vast majority of those who have keratoconus will never advance significantly, and for most it's correctable with glasses," he told Medscape Medical News.

Many patients with keratoconus can be treated with cross-linking and gas-permeable or advanced scleral contact lenses, he explained. However, if a surgical solution is needed, those with very steep but clear corneas unsuitable for a scleral lens might be candidates for the procedure.

And for those with poor vision because of corneal scarring, "a Bowman's membrane transplant isn't going to help you because the issue isn't contour, it's clarity," he pointed out.

In the very small subset of people who could benefit, "an anterior procedure that largely eliminates the risk of rejection and does not produce the same degree of mechanical risk that a full-thickness or deep lamellar keratoplasty does is a clear advantage," he said.

The Bowman layer transplantation is promising, but will only serve a niche patient population, said Joung Kim, MD, from the section of corneal, external disease, and refractive surgery at Emory Eye Center in Atlanta.

The technique leaves the integrity of the eye essentially intact, and the risk for allograft rejection is negligible, he explained. However, time and skill are required to prepare the Bowman's layer graft.

"Even if effective," said Dr Kim, "it will likely not become a common procedure unless the tissue can be prepared by the eye bank."

In the United States, a donor eye cannot be used for multiple procedures in different patients, so the increased need for suitable tissue that would result from the widespread use of this technique would strain the eye bank system, he pointed out.

Dr Parker is a consultant for Dutch Ophthalmic Research Center International. Dr McLeod and Dr Kim have disclosed no relevant financial relationships.

American Academy of Ophthalmology (AAO) 2016 Annual Meeting: Abstract PO356. Presented October 17, 2016.


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