This Rabbit Test Suggests Glaucoma Relief for Humans : Medicine: Tiny disc placed on eyes lowers fluid pressure, which can damage the optic nerve and lead to blindness.

A tiny disc placed on the eyes of rabbits released a substance that lowered the fluid pressure inside their eyeballs, suggesting a possible new approach to treating glaucoma.

In glaucoma, which affects perhaps 3 million Americans age 40 and over, excessive fluid pressure in the eye can damage the optic nerve and lead to blindness.

Most cases are treated with eye drops. But they can cause side effects, patients do not always take them, and they eventually stop working in many patients.

If drugs fail, doctors can use a scalpel or laser to make a tiny hole that lets excess fluid leak out. But that hole can become plugged or heal up, ending the procedure’s effectiveness, and making a hole carries risks of surgical complications, said researcher Dr. Jacob Dan.

In the experimental procedure, an enzyme released by the disc thins the white of the eye underneath. That lets fluid drain through the tissue without creating a major hole.

Dan, with Arieh Yaron of the Weizmann Institute of Science in Rehovot, Israel, reports the work in the March issue of the journal Ophthalmology. Dan is affiliated with the institute and the California Pacific Medical Center in San Francisco.

Dan said human experiments are expected to begin soon, but he stressed that it is not yet clear whether the disc will work in people. Even if it does work, it will be years until it could be widely available, he said.

The Ophthalmology article reported results in 15 rabbits without glaucoma. In each animal, the fluid pressure of the two eyes was virtually the same before treatment.

Researchers applied the disc, which was less than one-third the size of a small hard contact lens, to one eye in each animal under local anesthesia. The disc did not disturb eye movement or blinking for the four hours it was in place, Dan said.

During that time, an enzyme called collagenase released from the disc thinned the tissue below by more than three-fourths its original width, researchers found.

Pressure in the treated eyes was initially reduced by 40% to 60% below that of the untreated eyes. The reduction narrowed to about 20% from the 10th through the 30th day after the procedure.

The effect lasted more than twice as long as has been seen with surgical treatment in rabbits, the researchers said.

No side effects were seen, other than some slight and temporary irritation where the disc had been applied, Dan said.

“It is promising and exciting,” commented Dr. Eve Higginbotham, an associate professor of ophthalmology at the University of Michigan’s Medical School in Ann Arbor.

But she cautioned that its effectiveness in people is not known, and that the technique would have to be refined before it could be useful in most patients.