Small-particle air pollution may raise risk of glaucoma in some people

In people who already have a genetic vulnerability, small-particle air pollution known as black carbon may raise the risk of developing glaucoma, a new study suggests.

Researchers found that in older men with genetic variations that made them especially susceptible to oxidative stress, long-term exposure to black carbon, a pollutant linked to vehicle emissions and other products of combustion, was associated with higher pressures in the eye, according to the study published in JAMA Ophthalmology.

“Oftentimes, when we think about glaucoma we think about risk factors like age and genetic predisposition and we don’t think about the environment,” said the study’s lead author, Jamaji Nwanaji-Enwerem, an MD/PhD candidate at the Harvard Medical School in Boston. “But one thing we’re starting to appreciate more is how the environment impacts health outcomes.”

One area in which there hasn’t been a lot of research is the impact of the environment on eye disease, Nwanaji-Enwerem said. So, he and his colleagues decided to look at the effect of the tiny particles of black carbon, which are smaller than 2.5 microns in diameter and can penetrate deep into the lungs, and from there, into the bloodstream.

The researchers analyzed data from 419 older men from the Boston area who had been participating since the 1960s in a larger U.S. Department of Veterans Affairs aging study. They came in for health exams every three to five years after joining the study and as part of those exams intraocular pressure was measured.

Glaucoma, which can eventually result in blindness if not treated, is most often caused by high intraocular pressure, or high fluid pressure within the eye.

 “When eye pressure is too high, it causes damage to the optic nerve, the cable that connects our eyes to the brain and visual pathways,” explained Dr. Christopher Starr, an ophthalmologist at NewYork-Presbyterian/Weill Cornell Medicine in New York City, who was not involved in the new research. “If you lose cells in that nerve, you lose vision. It usually starts with peripheral vision loss and as time goes on you lose more and more.”

For the study, Nwanaji-Enwerem’s team determined the men’s pollution exposure using a modeling program that included black carbon levels gleaned from 83 monitoring sites and weather data.

The researchers then analyzed the pollution results along with each man’s eye pressure readings and a host of other health and lifestyle factors, including BMI, smoking status, heart disease, blood pressure and diabetes.

Overall, they found no link between pollution and eye pressure. But when they looked just at men who had certain gene versions that made them vulnerable to oxidative stress, the researchers found an association between higher pollution levels and a slight increase in eye pressure.

While interesting, the new study’s findings will need to be duplicated, Starr noted, adding that even if proven, the effects seen in this study are small. “They may not even be clinically significant in the context of glaucoma,” he said.

The differences in intraocular pressure might have been more striking if the men in the study had lived in a place that had high levels of black carbon pollution, Starr said.

While it’s clear that family history can raise your risk for glaucoma, studies of other possible variables have been mixed, said Dr. Julia Polat, an assistant professor of ophthalmology at the University of Pittsburgh Medical Center in Pennsylvania, who was not involved in the new research.

 “When patients ask, ‘what can I do to modify my risk?’ unfortunately I don’t have a lot of definitive information to give them,” Polat said. “I tell them to eat healthy, exercise and stop smoking, not necessarily because it will help with glaucoma, but because these changes can make them healthier overall.”

Glaucoma is especially insidious because it generally develops with no symptoms, Starr said. That’s why people should be getting their pressures checked on a regular basis, he added.

 “One of the ironic things, if you look at global surveys in almost all societies and cultures vision is by far what people cherish and value most,” Starr said. “And yet, people see their GP for yearly checkups, but don’t see an eye doctor regularly.”