In people who already have genetic vulnerability, small particle air contamination known as black coal can increase the risk of developing glaucoma, according to a new study.
Researchers have found that older men with genetic changes that are particularly susceptible to oxidative stress, long-term exposure to black carbon, a pollutant associated with vehicle emissions and other combustion products, were associated with increased pressure in the eye, according to a study published in JAMA ophthalmology.
"Often, when we think of glaucoma, we think about risk factors such as age and genetic predisposition, and we do not think about the environment," said chief study author Jamaji Nwanaji-Enwer, MD / PhD candidate at Harvard Medical School in Boston. "But one thing we start to appreciate is how the environment affects the health of the outcome."
One area where there was not much research is the environmental impact of eye disease, Nwanaji-Enwer said. So he and his colleagues decided to look at the effect of tiny black carbon particles, which are smaller than 2.5 microns in diameter and can penetrate deep into the lungs and then into the bloodstream.
The researchers analyzed data from 419 older Boston-born men who had been involved since the 1960s in a larger American study of the aging US Veterans' Ministry. They came to medical examinations every three to five years after joining the study, and intraocular pressure was measured as part of these studies.
Glaucoma, which can result in blindness if not treated, is most often caused by high intraocular pressure or high pressure of fluid 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 the visual pathways," explained Dr. Christopher Starr, an ophthalmologist at New York-Presbyterian / Weill Cornell Medicine in New York, who was not involved in new research. "If you lose cells in that nerve, you lose sight, usually begins with peripheral loss of vision, and as time passes, you lose more and more."
For the study, Nwanaji-Enwer's team determined men's exposure by means of a modeling program that included black carbon levels collected from 83 surveillance sites and time data.
The researchers then analyzed the pollutants' results by reading the eye pressure of each human being and a number of other health and lifestyle factors, including BMI, smoking status, heart disease, blood pressure and diabetes.
Overall, they did not find the connection between pollution and eye pressure. But when they looked only at men who had certain gene versions that were subject to oxidative stress, researchers found the connection between higher levels of pollution and mild increase in eye pressure.
Although interesting, new research results will have to be duplicated, Starr noted, adding that even if proved, the effects seen in this research are small. "They may not even be clinically significant in the context of glaucoma," he said.
Differences in intraocular pressure could be more pronounced if men in the study lived in a place that had high levels of black carbon contamination, Starr said.
Although it is clear that family history may increase glaucoma risk, mixed studies of other possible variables are mixed, said Dr Julia Polat, Assistant Ophthalmology at Pittsburgh Medical Center, Pennsylvania, which was not included in the new study.
"When do patients ask," What can I do to change my risk? "Unfortunately I do not have a lot of definitive information I give them," said Polat. "I'm telling them to eat healthy, exercise, and stop smoking, not necessarily because they will help with glaucoma, but because these changes can make them healthier overall."
Glaucoma is especially obnoxious as it generally develops without symptoms, Starr said. That is why people should regularly check their pressures, he added.
"One of the ironic things, if you look at global research in virtually all societies and cultures, the vision is far from what people are most cherished and most costly," Starr said. "Yet, people see their doctors for annual examinations, but they do not regularly see the doctor's eye."
SOURCE: https://bit.ly/2JNqelK and https://bit.ly/2FlnQnE JAMA ophthalmology, online November 8, 2018.