NEW THERAPIES HOLD PROMISE FOR TREATING EYE DISORDER.

Byline: Colette Bouchez New York Daily News 

It's the leading cause of blindness in both young and old, and one in 10 people over age 65 is sure to be affected. The disease is macular degeneration. Normally, not even early diagnosis can save its victims' sight. This, however, soon may change.

Two new experimental therapies hold promise for revolutionizing treatment of this disease.

``We can't cure macular degeneration, but we may be able to halt the progression of blindness,'' reports Dr. Richard Rosen, now testing one of the new therapies at New York Eye and Ear Infirmary.

While no one is certain why macular degeneration develops, when it does, it occurs in one of two forms: the ``dry'' type, which rarely leads to blindness and normally requires no treatment, and the ``wet'' type, which is far more dangerous.

``In the wet form, an abnormal number of blood vessels begin rapidly growing at the back of the eye, just behind the retina,'' explains Dr. Anthony Berson, chairman of radiation oncology at St. Vincent's Comprehensive Cancer Center in New York, and a pioneer of one of the new treatments. The vessels usually begin to leak, depositing minute amounts of blood, fat and fluid, which in turn cause scars to form. ``That scarring is what ultimately destroys the vision,'' Berson says.

While doctors have long believed the key to treating macular degeneration would be to stop the vessels from leaking, doing so was not an easy task. Although lasers were a good beginning - they fuse vessels with heat - the strength of the beams needed to produce results increased the risk of damage to healthy eye tissue. As a result, only about 10 percent of patients with wet macular degeneration were eligible for treatment.

Now, however, there are two new options. Neither will restore eyesight that already is lost, but both offer new ways to stabilize vision and check the development of blindness.

The first - called photodynamic therapy - uses a laser beam in combination with photosensitive drugs. ``The theory is that certain chemicals - in this case a drug called tin ethyl etiopurpurin, or SnET2 - have an affinity for rapidly growing blood vessels,'' says Rosen. When administered (intravenously), the drug heads straight for the excess vessels and attaches itself to the cells. Within 20 minutes, doctors focus an extremely low-light laser beam into the eye.

``On its own, the beam is too weak to cause any damage,'' says Rosen. However, for the cells carrying the drug, it becomes a powerhouse of energy.

``The drug makes the cells so sensitive to the light, they react as if they were being hit with a much stronger beam,'' says Rosen. As a result, the laser is able to seal the vessels shut. But because the drug does not stick to the normal cells, they escape any laser damage.

``With the leakage stopped, the progression of blindness appears to be halted,'' says Rosen.

In the second new therapy, doctors use low-dose external beam radiation to accomplish much the same result.

``The beam passes through the side of the head, and into the area of the retina affected by the macular degeneration,'' Berson explains. The radiation seals the vessels, stopping leakage and preserving sight, all without harming other eye tissue.

The entire process requires just 10 two-minute treatments, administered during 10 days, with radiation exposure equal to no more than a chest X-ray.

Current studies show two-thirds of all patients who tried this form of radiation therapy retained stabilized vision for two years and counting. Doctors caution that both new treatments still are considered experimental.