Clinical Testing on Treatment for RP Is Underway
Evaluating RP therapy with hope and caution
People with retinitis pigmentosa have watched and waited for news of any treatment that might stop the progression of the disease or even allow them to recover lost vision. Now there is some reason to hope that a sustained release implant being evaluated at the U-M Kellogg Eye Center and 13 other centers across the nation could deliver the long-awaited therapy. Participants whose condition meets specific criteria will have surgery to receive an implant that releases a naturally occurring protein known to retard retinal degeneration. Today patients with retinitis pigmentosa (RP) have very few treatment options. Antioxidant vitamins may help, but they do not cure. There are no known effective treatments for these degenerative eye diseases that affect 100,000 Americans and, over time, can lead to blindness.
John R. Heckenlively, M.D., an internationally known expert on inherited retinal disease, will lead the study for the U-M Kellogg Eye Center. He is cautiously optimistic about the prospects for the new treatment because earlier research has demonstrated that the protein, ciliary neurotrophic factor (CNTF), has the ability to slow the degeneration of photoreceptors, the light-sensing cells essential for sight. Dr. Heckenlively, Paul R. Lichter Professor of Ophthalmic Genetics, explains that after a promising start in the early 1990s, the research on CNTF stalled for lack of a practical method to deliver the therapeutic protein to the eye. With the development of encapsulated cell technology by Neurotech USA, Inc., the delivery problem appears to have been solved.
The symptoms and severity of RP can vary, but the disease often begins with the loss of peripheral or side vision and difficulty seeing at night. As the disease progresses, an individual will have a narrower range of vision, resulting in tunnel vision. The remaining vision may or may not be clear and sharp.
“In light of the preliminary work on CNTF, there are high expectations for this new therapeutic technology,” says Dr. Heckenlively. “This is the first non-specific therapy to emerge with promising experimental results.” He adds that RP is difficult to treat, in part, because there are so many genetic forms. “Rather than targeting a particular type of RP,” says Dr. Heckenlively, “this new therapy focuses on the endpoint of all RP types: vision loss due to degeneration of photoreceptors.”
In 2005, a Phase I Clinical Trial concluded that the CNTF implant exhibited a safe profile for humans. Currently, two Phase II /III clinical trials are evaluating two different doses of CNTF: a high dose or a low dose in one eye, as well as a sham surgery in the other eye so participants will not know which eye has been treated with CNTF.
Vicki Parker, whose mother and grandmother both had RP, hopes to participate in the trial. “With my family history, I’m lucky. My mother and grandmother both had some vision in their final years,” she says. “Naturally, I’m always interested in the latest research. I’m hoping that if this study is successful, the treatment will become routine for people with RP and other types of eye diseases.”
For more information, see the Retina, Uveitis & Ocular Oncology Clinic at the Kellogg Eye Center.
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