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Subjects seeing better after use of CO2-enhancing drug

Eye redness was the clue that something was happening to Celia Ramirez's vision. Although she wasn't having trouble driving or doing other tasks, her children urged her to have a checkup. It turned out she was in the early stages of age-related macular degeneration (AMD), a disease that attacks a person's central field of vision.

Mrs. Ramirez, who lives in Mission in the Rio Grande Valley, had surgery that successfully controlled her eye pressure, but her central vision continued to deteriorate. Her specialist is William E. Sponsel, M.D., associate professor and director of research in the department of ophthalmology at The University of Texas Health Science Center at San Antonio (UTHSC). Dr. Sponsel's research led him to prescribe treatment with new combinations of medications. "These last two medicines he's had me on, they have really worked," Mrs. Ramirez said. "We've done a lot of praying. This is somewhat of a miracle."

The miracle involves carbon dioxide, which is crucial for vision. The healthy eye produces enough carbon dioxide to dilate blood vessels around the retina and maintain proper blood flow. The ailing eye does not produce enough. This holds important implications for the treatment of patients with blinding eye diseases such as AMD and glaucoma, which are marked by diminished circulation of blood in the back of the eye. Eye pressure also is a conventional barometer of eye health.

About 60 of 65 patients have seen their vision improve while receiving treatment at UTHSC's teaching hospital, University Hospital. "The patients are receiving combination drug therapy, including agents that trick the eye into retaining more of its carbon dioxide," Dr. Sponsel said. "We have patients with glaucoma and no AMD, patients with AMD and no glaucoma, and patients with both disorders. All appear to demonstrate benefit in the central visual area, regardless of the cause of that visual loss."

The Health Science Center is the first medical center to initiate this combination therapy for patients with central visual loss, Dr. Sponsel said. Considerable research yielded the conclusions that now help patients. "You don't expect these patients to get better, you expect them to get worse," he said. "We have seen dramatic results that bode well for treatment of these disorders in the future."

The researchers measure patients' sensitivity to light on visual function tests. An increase of 10 points represents more than a million-fold increase in actual visual acuity. Mrs. Ramirez's vision in the macula — the central visual area that enables perception of letters and colors — was scored as virtually zero on early tests. After the recent treatment, her score is now 24.

The miracle agents are called "carbonic anhydrase inhibitors" (CAI's). Given as eyedrops, CAI's reach the back of the eye rapidly and slow the clearance of carbon dioxide while increasing the supply of nutrients. They help dilate blood vessels within and behind the retina, which is the structure that receives, processes and transmits visual images relayed from the brain.

Dr. Sponsel pursued this line of research in an intriguing way — after discovering that adults who hyperventilated and rapidly blew off their body's carbon dioxide showed decreased vision, eye pressure and circulation in the back of the eye. He was treating subjects one week with a CAI called dorzolamide and the next week with placebo eyedrops. During hyperventilation, the subjects on dorzolamide maintained good light sensitivity in their central field of vision, while the same subjects during placebo treatment showed central visual loss.

Dr. Sponsel holds two U.S. patents on this work. One valuable aspect of the research is that it proves increased eye pressure is not necessarily the definitive indicator of eye vessel disease.

AMD affects 12 million Americans, including one of six between the ages of 55 and 64 and one of four between ages 65 and 74, according to the Macular Degeneration Foundation. Each year, 1.2 million will suffer severe central vision loss and 200,000 will lose all central vision in both eyes. Glaucoma affects an estimated 3 million Americans, according to the National Eye Institute.

Mrs. Fernandez is seeing more light at the end of the tunnel these days, thanks to the combination therapy Dr. Sponsel is testing. "Vision is precious," he said. "Despite the odds, she has had a beautiful retention of her ability to see."

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Contact: Will Sansom