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Eyesight to the blind.


Vision loss resulting from a potent radiation treatment can now be prevented and even reversed, say ophthalmologists at the University of Florida (UF) Eye Center. The blinding disorder, known as "radiation-induced optic neuropathy," is a rare but recognized risk of radiation therapy for brain tumors.

The radiation, designed to shrink tumors inside the head targeted by external beams, occasionally damages blood vessels supplying the optic nerve that enables the brain to register visual impulses. The answer, says UF ophthalmologists Dr. John Guy, is to expose the blind patient to high-pressure oxygen in a hyperbaric chamber, a pressurized, submarine-like tank that made the entertainment news a few years ago when singer Michael Jackson began using one as a preventive measure against aging. Although most physicians consider this usage to be mere quackery, the machine itself is anything but useless, having proven its effectiveness against decompression sickness (occurring whenever scuba divers encounter "the bends"), carbon monoxide poisoning, anemia, and skin graft rejection, among other ailments.

Vision can start to fade, says Guy, either while a patient is still receiving therapy, or afterwards. In fact, he says, blindness may not develop for several months or even years after treatment has ceased. This is why, he says, "the earlier a patient's vision loss is diagnosed, the greater their chances are that hyperbaric therapy will help them." Although quite rare ("We treat about one patient a year at the University of Florida," Guy says), radiation-induced blindness can still be emotionally devastating to people already distraught from their battle against cancer.

Hyperbaric therapy, Guy says, "has been shown to reverse vision loss within two weeks of sight loss, as well as permanently stop the progression of the blinding disorder." Guy first began hyperbaric therapy in 1983 and has treated five patients since. Of that number, two experienced total restoration of vision and a third patient's vision loss was nipped in the bud before total blindness occurred. Saturating the patient's body with three atmospheres of oxygen pressure--the equivalent of being 60 feet below sea level--for two-and-a-half hours a day over a two-week period, Guy says, allows the blood to deliver the extra oxygen directly to the affected area. As a result, vision is either partially or completely restored.

Guy is a pioneer in this form of therapy: "There previously was no treatment for cancer patients who lost their vision as a result of radiation therapy," he says. "Although radiation therapy might cure their tumors, there was no hope to prevent blindness if they developed optic neuropathy after the treatment." Guy adds, "Although radiation-induced blindness is very uncommon, cancer patients having to undergo radiation therapy to the brain can feel more comfortable knowing there is a treatment available if the adverse effect occurs."
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Title Annotation:hyperbaric therapy for radiation-induced optic neuropathy
Publication:Medical Update
Date:Apr 1, 1989
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