Bowman Layer Graft Strengthens Eyes With Keratoconus

Laird Harrison

February 24, 2014

Grafting donor Bowman layers into the corneas of patients with keratoconus may allow the patients to wear contact lenses longer, according to research by Korine van Dijk, BSc, from the Netherlands Institute for Innovative Ocular Surgery and the Melles Cornea Clinic Rotterdam, and colleagues.

If validated by further research, the technique would give surgeons another option for treating a progressive disease that can leave patients blind.

"It's a brilliant idea that saves the patient a lot of painful surgeries," coauthor Jack Parker, MD, told Medscape Medical News. van Dijk and colleagues published their findings online February 20 in JAMA Ophthalmology.

In keratoconus, the cornea gradually bulges outward in the shape of a cone, distorting the patient's vision.

Glasses and contact lenses can correct mild cases, and hard contact lenses can help in moderate cases, but in severe cases the distortion of the cornea may progress to the point that the contact lenses become too uncomfortable to wear.

At that point, keratoplasty or deep anterior lamellar keratoplasty may restore some vision, but these procedures come with the risk for infection, may not halt the progress of the disease, and can make the cornea vulnerable to injury, said Dr. Parker, ophthalmology resident at the University of Alabama in Birmingham.

More recently, surgeons have used ultraviolet A radiation to induce collagen cross-linking in patients with mild to moderate keratoconus. This procedure can halt the progression of the disease, but it requires expensive equipment. In addition, it may harm healthy cells in deep layers of the cornea in patients with thin corneas or advanced keratoconus, Dr. Parker said.

He and colleagues are proposing Bowman layer grafts as an alternative.

Coauthor Gerrit R.J. Melles, MD, PhD, came up with the idea, Dr. Parker said. Dr. Melles, an ophthalmologist at the Netherlands Institute for Innovative Ocular Surgery in Rotterdam, has a reputation for pioneering new cornea surgeries.

For the study, the researchers operated on 10 eyes in 9 patients with progressive, advanced keratoconus. At baseline, the patients were able to wear contact lenses for only "a few hours a day" because of the steepness of the bulge in their corneas.

The Bowman layer is a smooth, acellular, nonregenerating membrane that lies between the superficial epithelium and the stroma in the cornea, made up of collagen fibrils. The surgeons removed these membranes from donor corneas.

The researchers slit halfway through the thickness of the patients' corneas. Using blades of different sizes, they gradually dissected the corneas from 1 side to the other, creating a pocket. They then inserted donor Bowman layers and unfolded them.

As the corneas healed, the donor Bowman layers attached to the patients' corneas, and the incisions closed without sutures. "The fibrotic healing stiffens and pulls the cornea back toward a natural configuration," said Dr. Parker. "It does normalize the topography of the cornea a bit."

The surgeons reported improvement in several measures of the cornea topography a month after the surgery:

  • mean anterior simulated keratometry values decreased from 65.9 D (standard deviation, 5.4 D) before surgery to 59.5 D (standard deviation, 4.6 D) at 1 month (P = .001);

  • mean Kmax values dropped from 78.5 D (standard deviation, 6.3 D) to 69.9 D (standard deviation, 3.8 D) (P = .001);

  • mean posterior keratometry values rose from −10.2 D (standard deviation, 0.8 D) to −9.0 D (standard deviation, 0.5 D) (P = .005); and

  • mean maximum corneal power fell from 74.5 D (standard deviation, 7.1 D) to 67.2 D (standard deviation, 3.0 D) (P = .004).

A year after the surgery, the patients' corneas still maintained these improvements.

The patients' uncorrected vision did not improve significantly after 6 months, but after the surgery, they were all able to resume wearing contact lenses for a full day.

There were no complications to the surgeries, although "an intrastromal cavity was seen in some eyes within the first days after surgery," the researchers report.

Asked to comment, Ivan R. Schwab, MD, a clinical spokesperson for the American Academy of Ophthalmology, told Medscape Medical News he admired the virtuosity of the surgery. Because a cornea ranges in thickness from half a millimeter to 1 mm, creating a pocket inside one might be outside the skill of most ophthalmologists, he said.

"Dr. Melles is a gifted surgeon...it's not everybody who can do these procedures," said Dr. Schwab, director of the Cornea and External Eye Disease Service at the University of California Davis Health System Eye Center.

He said it is difficult to evaluate the procedure without knowing the measurements of the patients' vision, both with and without contact lenses, before and after the procedure. Those data were not included in the researchers' report.

He also wanted to know how the patients fared over the long term. "If their vision is really improved, if they can really see better to the point that they can drive and they can read, then I think this procedure is going to offer a lot to a relatively small number of people," he noted.

Most patients can already benefit from existing treatments, he said, and it is not clear how this procedure compares to surgeries already available.

Dr. Melles is a consultant for DORC International/Dutch Ophthalmic USA. The other authors and Dr. Schwab have disclosed no relevant financial relationships.

JAMA Ophthalmol. Published online February 20, 2014. Abstract

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