Antioxidant Supplements Don't Affect Intraocular Pressure

SAN FRANCISCO, California — A large epidemiological study is the first to report that high-dose supplements have no effect on intraocular pressure, the major risk factor for glaucoma.

"For people taking supplements in our study, there was no benefit in terms of reducing intraocular pressure (IOP)," lead investigator Thasarat Vajaranant, MD, from the University of Illinois at Chicago, Chicago, Illinois, told Medscape Medical News.

"Our results don't provide any evidence that high-dose antioxidants would protect against glaucoma through an IOP reduction," Dr. Vajaranant said of the research presented here at the American Glaucoma Society (AGS) 23rd Annual Meeting.

In the study, researchers analyzed data on 3017 subjects in the Age-Related Eye Disease Study (AREDS) in which participants were randomized to high-dose antioxidants — including beta carotene, vitamin C, vitamin E, and zinc — or placebo.

AREDS found that high-dose antioxidants can protect against macular degeneration, but the University of Illinois at Chicago researchers wanted to assess whether the supplements had an effect on intraocular pressure.

Basic research indicates that oxidative damage to the trabecular meshwork may compromise drainage and increase intraocular pressure, Dr. Vajaranant said. Several large epidemiologic studies have looked at the question of whether diets high in antioxidants can protect against glaucoma, but their results have been conflicting, she noted.

Findings From AREDS

For their study, the researchers analyzed data on 3017 AREDS participants collected at 5 and 10 years after randomization, including IOP measurements.

The AREDS study excluded patients with glaucoma, and the University of Illinois at Chicago researchers excluded those who reported glaucoma during the study.

At 5 years after randomization, IOP data were available on over 1400 patients in the AREDS study. After 5 years, the mean IOP for the 739 patients in the high-dose supplement group was 15.8 vs 15.7 for the 719 patients in the placebo group.

At 10 years, data on IOP were available for 618 patients in the antioxidant group and 582 patients in the placebo group. Again, there was no difference in IOP between the two groups — with a mean IOP of 15.8 for the subjects who took antioxidants vs 15.7 for those who took placebo.

Still, the researchers' conclusion — that their study fails to support a protective effect of antioxidants against glaucoma — is too far reaching, Anne Coleman, MD, from the University of California at Los Angeles, Los Angeles, California, told Medscape Medical News.

Although the study did not detect a link between high-dose antioxidants and eye pressure, it does not automatically follow that high-dose antioxidants have no implications for glaucoma, according to Dr. Coleman, Fran and Ray Stark professor of ophthalmology and professor of epidemiology at UCLA.

"Since those who had glaucoma at baseline were excluded, and the investigators excluded those who reported it during the study, all we know is the effect on eye pressure, not on glaucoma," Dr. Coleman said.

Dr. Coleman's own research has suggested a link between antioxidants in food and a protective effect against glaucoma. "But associations in the data do not prove causality," she said.

"Whether or not high-dose antioxidants might protect against glaucoma is an interesting question," Dr. Coleman added, "but studies to date have not provided definitive answers."

The investigators and Dr. Coleman have reported no relevant financial relationships.

American Glaucoma Society (AGS) 23rd Annual Meeting: Abstract 87. Presented March 2, 2013.