Clinical News
MEDICAL AND PRODUCT UPDATES

ARTIFICIAL ORGANS
Corneas, retinas --and eyes

The latest developments in man-made organs:

	Frog eyes grown from embryonic cells have allowed blind tadpoles to see.

Artificial corneas. Researchers at the Lions Eye Institute of Western Australia have developed the world's first flexible artificial cornea, named AlphaCor. The one-piece plastic device is similar to a donor graft in dimensions and flexibility, and is designed to replace a diseased or damaged cornea or failed human graft.

The AlphaCor has been implanted in 41 patients since 1998 who have been followed for up to 3 and a half years. The AlphaCor reportedly has a better than 80% 1-year success rate; some patients regained vision after many years of blindness.

Artificial retinas. Six patients who had lost their vision because of retinitis pigmentosa have been implanted with artificial silicon retinas. Although some of the patients were virtually blind, all regained limited vision.

The patients are part of a pilot study of a solar-powered microchip created by Optobionics, a private company based in Wheaton, Ill. The microchips, which convert light into electrical impulses, are smaller than the head of a pin and about half the thickness of a sheet of paper. They were surgically implanted behind the retina. In addition to the positive vision results:

• No inflammation, rejections or detachments have occurred.
• None of the chips has eroded or moved.
• None of the patients has experienced any pain or discomfort.

The chips also seem to be stimulating the remaining healthy retinal cells. Researchers report that vision is improving not only where the implant is but also in areas near the implant.

Artificial eyes. Professor Makoto Asashima, a leading embryologist at Tokyo University, has successfully grown artificial frog eyes in a test tube using cells from frog embryos. After transplanting them into 60 blind tadpoles, about 70% were able to see.

The work was reported at the 29th International Congress of Ophthalmol-ogy, held in Sydney, Australia in April.

REFRACTIVE SURGERY
Implantable contact lens

The world's first implantable contact lens -- a synthetic lens that is placed under the corneal epithelium -- could be on the market within 5 years. The device is being developed at the Cooperative Research Centre for Eye Research and Technology (CRCERT) at the University of New South Wales in Australia.

During implantation, the epithelium is removed; the lens is placed on the debrided surface, and the epithelium is allowed to regrow over the new lens. The procedure is permanent but reversible.

Although work on the lens is 70% complete, a lack of financing has temporarily stalled the project.

SURGICAL COMPLICATIONS
Healing without scarring

Tissue scarring following surgery helps to cause the failure of treatments for many blinding eye conditions, including glaucoma. Now, researchers are finding ways to duplicate the scarless healing that occurs following surgery on fetuses in the womb.

Peng Tee Khaw, professor and ophthalmic surgeon at the Institute of Ophthalmology and Moorfields Eye Hospital in London, has used a human antibody to neutralize a protein normally found in the healing process -- except in fetal wounds. Without this protein, called transforming growth factor beta, wounded eye tissue slowly regenerates, producing permeable tissue with minimal scarring.

CATARACT SURGERY AFTER PRK
Calculating lens power accurately

A nonrandomized, retrospective clinical study conducted in the Netherlands compared post-op refraction predictions to actual refractive outcomes when cataract surgery was performed on nine patients (15 eyes) who had had prior PRK to correct myopia.

Using eight different keratometric (K) values and three different IOL calculation formulas (SRK/T, Holladay 1, and Hoffer Q) researchers compared predictions (based on actual biometry and IOL parameters) to final refractive outcomes. They found:

• The most accurate K value for IOL calculation was the pre-PRK K value, corrected by the spectacle plane change in refraction.
• Use of the Hoffer Q formula would have avoided postoperative hyperopia in more cases than the other formulas.
• The mean underestimation of the change in corneal power after PRK varied from 42% to 74%, depending on the method of calculation.

The study appeared in a recent issue of Archives of Ophthalmology.