Corneal onlays in early stages of development

Lynda Charters

San Francisco-Early experience with the use of corneal onlays for refractive correction seems to indicate that extracellular matrix substitutes can be made into onlays that can integrate functionally within host corneas. Epithelial pockets can be created and there is potential for these lenticules to be useful future supplements for, or alternatives to, laser-based refractive correction, according to W. Bruce Jackson, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

"The idea surrounding this work is to put a corneal onlay above Bowman's membrane under the epithelium that would allow the correction of ±6 D and some astigmatism," Dr. Jackson said. "In addition, the procedure is noninvasive, reversible, causes minimal discomfort, and results in rapid visual recovery."

Another advantage to this technology would be the ability to ablate the onlay as well, he pointed out.

"Dr. Griffith has been cross-linking a porcine collagen and synthetic materials to increase stability and strength," he said. Investigators are also working with human recombinant collagen, the properties of which are similar to the porcine collagen.

The corneal onlays and inlays have been implanted in pigs for up to 12 months.

"The nerve growth that will grow into this material is visible, and the implants remain clear," said Dr. Jackson.

Epithelial pocket creation

The manufacturer Gebauer developed a delaminating device for creation of an 8-mm pocket under the epithelium and above Bowman's membrane.

"The creation of the pocket has been extremely reproducible," Dr. Jackson said. "One area for improvement is to narrow the entrance to the pocket, but we are still in the early stages of this procedure."

He demonstrated on electron micro-scopy slides the separation between Bowman's membrane and the basement membrane that was still attached to the epithelium.

"The separation between the two is very clean," he emphasized.

The first onlay was implanted in a human during a procedure performed in Bogotá, Colombia. The patient was a woman with keratoconus who was to undergo a corneal transplant. Dr. Jackson was amazed the device used to create the pocket works extremely well in eyes with keratoconus and the pocket is created cleanly.