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Oxygen = Glaucoma?

More Oxygen in the Eyes of African Americans May Help Explain Glaucoma Risk

Measuring oxygen during eye surgery, investigators at Washington University have discovered a reason that may explain why African Americans have a higher risk of glaucoma than Caucasians.

They found that oxygen levels are significantly higher in the eyes of African Americans with glaucoma than in Caucasians with the disease. The researchers report their findings in the July issue of the Archives of Ophthalmology. They suspect that more oxygen may damage the drainage system in the eye, resulting in elevated pressure.

The study provides the first physiologic clue about the link between race and risk for glaucoma, which is the leading cause of blindness among African Americans. Compared to Caucasians, glaucoma is about six times more common in African Americans, and blindness caused by glaucoma is roughly 16 times more likely in African Americans.

“Our findings suggest there may be physiologic differences in oxygen metabolism between African Americans and Caucasians,” says first author Carla Siegfried, MD, a Washington University ophthalmologist at Barnes-Jewish Hospital. “In our studies, we were not looking specifically at African Americans, but the racial difference in oxygen levels was significant, and we believe this observation deserves further study.”

Siegfried says it’s not surprising that oxygen may play a big role in the development of glaucoma because it may be a source of free radicals that damage cells. Oxidative stress, an imbalance between these free radicals and antioxidants, is linked to the aging process and many other age-related conditions such as cardiovascular and neurodegenerative diseases.

The researchers measured oxygen levels in the eyes of patients who were having surgery for cataracts or glaucoma or both. Because all the patients were having eye surgery, the researchers did not have a comparison or control group. But the African American patients having surgery often were younger than Caucasians.

“Glaucoma often affects African Americans at a younger age,” Siegfried says. “And when we used statistical methods to adjust for differences in age, the difference in oxygen levels between African Americans and Caucasians became more significant. Then, when we controlled for racial differences, we found that increased age became an important indicator of elevated oxygen levels in certain locations in the front part of the eye.”

Siegfried says it is not yet possible to say whether the elevated oxygen levels cause pressure to rise and optic nerve damage to occur, but she says higher levels of oxygen are clearly associated with factors, like race, that carry increased glaucoma risk. Her team has received a four-year grant from the National Eye Institute to further investigate that association.

“When we understand the underlying reason for elevated oxygen and how it may damage the eye, we will be in a better position to develop ways to prevent this disease,” Siegfried says.

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