New types of soft plastics being manufactured by a Pasadena company and tested at UCLA may soon replace those currently being used in artificial lenses implanted in the eyes of cataract victims, reducing long-term damage to the eye from such lens implants, researchers said Monday.
Similar plastics can also be used as artificial corneas and perhaps reduce reliance on corneal transplants, which are frequently rejected, the researchers told a meeting of the American Chemical Society in Los Angeles.
The new materials, which are just starting to be tested in humans, could find wide use. More than 1.2 million Americans--90% of all cataract victims--received intra-ocular lens implants during cataract operations last year, and more than 2 million people worldwide, according to materials scientist Eugene P. Goldberg of the University of Florida in Gainesville.
And about 30,000 Americans received corneal transplants in the same year after chemical burns to the eyes or as a result of immunological disorders that damaged the cornea, according to chemist Jean T. Jacob-LaBarre of the Tulane University School of Medicine in New Orleans. About 6,000 of those recipients have already rejected or will reject the new corneas, she said.
Problems With Plastic
A plastic called polymethylmethacrylate is now used for intra-ocular lenses and, to a limited extent, as an artificial cornea, but it produces problems in both applications. The hard plastic intra-ocular lens is inserted in the eye just behind the pupil. In some cases, the iris of the pupil can stick to the plastic, becoming damaged in the process.
The hard surface of the lens, furthermore, can irritate and inflame adjacent tissues.
Goldberg devised a chemical technique for coating the surface of conventional polymethylmethacrylate with a second plastic, similar to that now widely used in soft contact lenses, that absorbs water and becomes both soft and slippery. The iris thus cannot stick to the lens and other tissues slide smoothly over it.
Goldberg has licensed the technique for coating the lenses to Pharmacia Ophthalmics Inc. of Pasadena. Pharmacia is sponsoring clinical trials of the lenses at six U.S. medical centers, including UCLA. Nearly 200 lenses have been implanted and the company hopes to have Food and Drug Administration approval for marketing the lenses by the end of 1989, Goldberg said.
Rigidity a Problem
Artificial corneas can produce some of the same problems as the hard-plastic intra-ocular lenses. But even more important, Jacob-LaBarre said, their rigidity frequently causes them to be sheared free from the flexible surface of the eyeball.
Jacob-LaBarre and Tulane ophthalmologist Delmar R. Caldwell have developed an artificial cornea in which the center is a clear plastic lens similar to those now used. Attached to the rim of the lens, however, is a ring of porous, water-absorbing plastic with six "spokes" extending radially outward.
The artificial cornea is placed on the surface of the eye and each of the six spokes is sutured to the side of the eyeball. Tissue then grows around them and into the pores to anchor the cornea.
Caldwell implanted the cornea in a human for the first time last December, and has subsequently performed two more implants. He has approval from the FDA to treat 12 patients.