A recent study found that heavier women were less likely to get one type of glaucoma than their thinner peers - the first time this association has been shown, the authors report.

The finding doesn’t mean that anyone at risk for the disease should try to pack on the pounds, they say, but it could be a first step towards learning more about why people develop glaucoma and how it progresses.

Glaucoma is a degenerative eye condition that occurs when there is damage to the optic nerve - fibers that run between the eye and the brain. According to the Glaucoma Research Foundation, more than 4 million Americans, mostly older adults, have glaucoma. Common treatments for glaucoma include medicated eye drops and other drugs as well as surgery.

Researchers have suspected that heavier people might be more at risk for glaucoma. A higher body mass index (BMI) - a ratio of weight to height - means people are more likely to have diabetes, and diabetes could be linked to the rising inner eye pressure that is seen in many glaucoma cases, the authors write.

But their findings suggest a different pattern.

Led by Dr. Louis Pasquale, researchers from the Harvard Medical School and Harvard School of Public Health followed about 120,000 middle-aged adults who are part of two long-term studies of healthcare workers. Over the course of at least 18 years, study participants filled out questionnaires every other year that asked for lifestyle and health information such as weight, diet, and diagnosed medical conditions.

About 8,300 of the participants reported in their questionnaires that they had been diagnosed with glaucoma at some point during the study. The authors narrowed this down to approximately 1,000 cases that they could confirm with the patients’ doctors and on their own.

One previous study found that around 4 percent of adults age 40 and over have glaucoma.

After picking out the confirmed glaucoma cases, the authors looked at how likely patients were to have glaucoma based on their BMI.

Women with a higher BMI and higher weights were less likely than thinner women to develop a certain type of glaucoma, called normal tension glaucoma, which occurs when pressure in the eye isn’t any higher than normal.

For every unit of increase in BMI - equal to about a 6-pound gain in a woman of average height and weight - a woman’s risk for normal tension glaucoma dropped by 6 percent. Women who reported that they had been heavier for their height as young adults were also less likely to develop this kind of glaucoma.

In women with higher inner eye pressure and in all men, there was no link between BMI or body weight alone and how likely a person was to get glaucoma.

The reason why weight might protect women against glaucoma isn’t completely clear, but Pasquale thinks it could have something to do with estrogen. “Our hypothesis is that women with higher BMI have higher circulating estrogen levels than women with lower BMI,” Pasquale told Reuters Health by email. It might be that estrogen helps keep the optic nerve working, he said.

Differences in body composition between men and women, and in the amount of estrogen they produce, could help explain why there is a link between weight and glaucoma risk in women but not men, Pasquale added.

Height had no association with glaucoma risk in men or women in the study, which is published in the journal Ophthalmology.

One limitation of the study, the authors write, is that the participants were mostly white - and glaucoma is much more common in African-Americans.

Pasquale and his colleagues are trying to dig deeper into the connection between weight and glaucoma in women to better explain their findings. In the meantime, Pasquale said, the results should not change anything about the way doctors treat patients with glaucoma or those at risk for the condition.

SOURCE:  Ophthalmology, August 2010.