THURSDAY, Aug. 5 (HealthDay News) -- While maintaining a healthy weight is linked to a lowered risk of heart disease and diabetes, being overweight may actually protect some women from a form of glaucoma, Harvard researchers say.

This new finding suggests that overweight women may have a lower risk of developing primary open-angle glaucoma (POAG), one of the most common age-related eye diseases. In particular, overweight women may be especially protected from a variant of POAG called normal-tension glaucoma, the researchers say.

"While being overweight has many negative health consequences, increased risk of primary open-angle glaucoma was not one of them," said lead researcher Dr. Louis R. Pasquale, director of the Glaucoma Service at the Massachusetts Eye and Ear Infirmary and an associate professor of ophthalmology at Harvard Medical School.

"While this study was a comprehensive assessment of the relation between body shape and glaucoma, it should not lead to recommendations about adopting an ideal body weight to prevent glaucoma," he added.

The report is published in the August issue of Ophthalmology.

For the study, Pasquale's group collected data on 78,777 women in the Nurses' Health Study and 41,352 men in the Health Professionals Follow-up Study.

The researchers found that each unit increase in body mass index (BMI) was associated with a 6 percent lowered risk for normal-tension glaucoma. BMI is a measurement that takes into account a person's height and weight.

In addition, women with a high BMI when they were young also had reduced risk of developing normal-tension glaucoma.

Among men, there was no association between BMI and the risk for POAG, the researchers noted.

Since most of those in the study were white Europeans, these findings may be limited to similar patients, they added.

Glaucoma is a potentially blinding illness that damages the optic nerve. Increased pressure in the eye is linked to optic nerve damage. Effective treatments to control eye pressure are available. But in people with normal-tension glaucoma, optic nerve damage happens even though their eye pressure is not high, the researchers noted.

"There is no stereotypical body shape associated with primary open-angle glaucoma, but the negative relation we found between body mass index and the normal-tension variant of primary open-angle glaucoma in women may give some clues regarding eye-pressure independent mechanisms of optic nerve deterioration in this disease," Pasquale said.

"We postulate that fatty tissue in the body may release hormonally related signals that help prevent optic nerve deterioration in glaucoma," he said.

Dr. Krishna S. Kishor, an assistant professor of clinical ophthalmology at the Bascom Palmer Eye Institute of the University of Miami Miller School of Medicine, said usually there is a connection between being overweight and increased eye pressure and a loose correlation between glaucoma and diabetes, which often affect the obese.

"But in overweight women some hormones may be binding with the retina and may be protecting these women from getting glaucoma," he said.

However, Kishor is cautious and thinks more research is needed to see if this correlation holds true. For example, blacks, who are more susceptible to glaucoma, were not well-represented in the study, he noted. In addition, these data were self-reported, which is not always accurate, he added.

In any case, people should not put on weight in hopes of preventing glaucoma, Kishor said. "Don't gain weight thinking that it might somehow protect you," he said.

More information

For more information on glaucoma, visit the U.S. National Library of Medicine.