Retinitis pigmentosa

Testing an experimental treatment that they liken to replacing old, deteriorated film in a camera with a fresh roll, scientists have begun injecting cells harvested from the eyes of aborted fetuses into the eyes of people with retinitis pigmentosa, the most common inherited cause of blindness.

This week, researchers involved in the effort claimed that five of the first eight patients who received the fetal cells have experienced discernible, though extremely limited, improvement in vision. Such cell transplants are unlikely ever to restore completely the eyesight of people with retinitis pigmentosa, but even a small improvement in vision would be welcome and useful, says Manuel del Cerro of the University of Rochester (N.Y.) School of Medicine and Dentistry, who reported the initial results of the cell transplants at a Society for Neuroscience meeting in Washington, D.C.

Retinitis pigmentosa, which afflicts several million people worldwide, slowly robs a person of sight by destroying the photoreceptor cells that line the eye's retina. The light-sensitive cells, commonly known as rods and cones, convert incoming images into patterns of electric impulses that travel through other retinal cell layers and finally to the brain.

For more than a decade, del Cerro and other researchers have investigated whether rods and cones ravaged by retinitis pigmentosa could be replaced with new photoreceptors (SN: 11/4/89, p. 297). In 1991, del Cerro's group found that fetal eye cells implanted into the eyes of blinded rats partially restored the animals' ability to perceive light (SN: 11/23/91, p. 325).

Those results encouraged del Cerro to collaborate with eye surgeons at the L.V. Prasad Eye Institute in Hyderabad, India, on a human trial. The surgeons selected eight retinitis pigmentosa patients whose vision had deteriorated to the point where they could only perceive the difference between light and dark. Working on one eye of each patient, the surgeons made a small incision in the retina and injected about 1 million fetal eye cells into the space beneath the incision.

Their hope was that the fetal eye cells, which had yet to differentiate into any one cell type, would develop predominantly into new photoreceptors and establish the retinal connections needed to convey visual information.

It took 4 to 6 months before any of the patients reported an improvement in vision, says del Cerro. Two of the patients now detect hand motion, he says. Two others can reportedly count fingers held up at a short distance.

The fifth patient can now recognize faces and walk around unaided, thanks to the development of a tiny field of view in which he has 20/200 vision. It's "a little keyhole view of the world," says del Cerro.

Several retinal transplant researchers contacted by Science News argue that the trial in India should have included an independent evaluation of each patient's vision before and after the surgery.

"I simply don't believe these results," says Peter Gouras of Columbia University, who has experimented with cell transplants for a retinal disease called age-related macular degeneration.

Other vision researchers privately echo Gouras' skepticism, and some raise the issue of whether there has been sufficient evidence that cell transplants work in animals to justify the decision to start trials in humans.

Undeterred by the criticism and buoyed by the apparent success of the first trial, del Cerro and his colleagues have already started additional human trials in India and at Johns Hopkins Medical Institutions in Baltimore. A research group led by Henry Kaplan of Washington University in St. Louis is ready to start its own human trial of the cell transplant strategy, using photoreceptors harvested from adult eyes.

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