Uprooting a major cause of blindness.

Uprooting a major cause of blindness

A new laser technique developed by a husband-and-wife research team shows promise as a treatment for age-related macular degeneration, the most common cause of irreversible blindness in U.S. adults over 65 years old. The condition begins with a proliferation of leaky blood vessels under the macula, or central portion of the retina, causing damage and scarring followed by progressive blindness.

The macula -- 100 times more sensitive to visual detail than other parts of the retina -- is essential to such activities as reading fine print, driving a car and recognizing faces. Nobody knows why the underlying blood vessels so often begin to proliferate late in life. But early detection and ablation of these leaky vessels is critical, since the light-detecting macular cells won't recover once they're damaged by the seeping blood plasma and other fluids.

Opthalmologists already use lasers to destroy proliferating vessels in some patients with early macular degeneration. This prevents the vessels from disrupting the delicate retinal architecture and stanches the leakage of damaging fluids. But the treatment's value remains limited to the 25 percent of cases in which only a few, easily targeted abnormal vessels have developed. Most cases involve many abnormal vessels scattered beneath the macula, leaving opthalmologists uncertain where to aim the beam. And because each laser hit destroys a tiny portion of the retina, wholesale lasing of every leaky vessel might take too heavy a toll on visual acuity.

Neil M. Bressler and Susan B. Bressler of the Johns Hopkins University School of Medicine started a pilot trial one year ago for patients with diffuse macular vessel proliferation. Using krypton and tunable dye lasers, they applied tiny laser hits in a grid pattern over the back of the retina. The treatment gives the retina the appearance of a miniature pegboard, with hits 150 microns apart, but it leaves the vast majority fo the retina intact while zapping a significant number of abnormal blood vessels, the researchers say. Moreover, they report indirect evidence that the treatment may prompt certain specialized retinal cells to release so-called anti-angiogenic factors, which suppress vessel proliferation.

As of July, the Bresslers had treated 53 patients. They say the results are encouraging; in some cases the treatment has let to complete elimination of retinal fluid leakage within six weeks.

Many more patients must receive the experimental treatment before its usefulness can be confirmed, the researchers add. And since scientists don't really know what ultimately causes blindness in victims of macular degeneration, it remains unclear whether the anatomic improvement achieved with laser treatment will ultimately preserve patients' vision. The Bresslers hope to answer that question within another year.

Meanwhile, in the October ARCHIVES OF OPHTHALMOLOGY, they will report results from the first large-scale, prospective study seeking to identify those people at highest risk of developing age-related macular degeneration. The Hopkins team examined a five-year series of retinal photographs from 127 people who developed macular degeneration, tracking the changes in various cellular features. From those data, they created a predictive diagnostic formula that identifies those patients at highest risk of developing the vision-threatening vessel profusion.