An increased risk of glaucoma can be added onto the hefty list of negative consequences of pollution. Photo: Getty Images.

Most people think of respiratory illness when considering the adverse health effects of poor air quality—and rightfully so—but it also contributes to a number of less obvious issues, including rates of diabetes and glaucoma. Particles smaller than 2.5µm (PM2.5) are known risk factors for diabetes, and diabetes itself is a risk factor for glaucoma. Because PM2.5 has been demonstrated to induce the expression of hypoxia-inducible factor 1-alpha in mice, first causing retinopathy and then glaucoma, researchers recently examined whether the risk of glaucoma changes when diabetes patients are exposed to different PM2.5 concentrations. They found that PM2.5 not only increases the risk of glaucoma but also represents an independent risk factor for glaucoma in patients with diabetes.

The researchers obtained data from the National Health Insurance Research Database of Taiwan and the Air Quality Monitoring Network from 2008 to 2013. Their nested case-control study included 197 diabetes patients with glaucoma and 788 diabetes patients without glaucoma.

The Migraine Connection

Migraine is sometimes defined as a vascular and neurological disorder, with pain often attributed to trigeminal neurovascular system activation. In their study, the researchers noted that patients without migraine had an OR of glaucoma of 1.7. “Change in blood vessel diameter may relate to vascular disorders or vasospasms,” they said. “Therefore, the common underlying pathophysiological mechanism could be the link between glaucoma and migraine.”

Though the literature is inconsistent regarding the association between migraine and glaucoma, the current study found that both the degree of migraine and the degree of urbanization affect the risk of a patient with diabetes developing glaucoma. The researchers believe there may be a positive correlation between migraine and glaucoma because exposure to higher concentrations of PM2.5 was an independent risk factor for glaucoma. However, the relationship is complex and the role diabetes plays still requires further research.

The researchers reported that the odds ratio (OR) of glaucoma at PM2.5 exposure concentration in the fourth quartile compared with the first quartile was 1.7. “For glaucoma risk, the OR was 1.013 at a PM2.5 exposure concentration in the first quartile, 1.004 in the third quartile and 1.003 in the fourth quartile,” they said. “In the subgroup analysis of patients living in non-emerging and non-agricultural towns, the ORs of glaucoma in the fourth quartile compared with the first were 2.1 and 1.8, respectively.”

“Epidemiological studies have become significantly important in this aging society with chronic disease,” the researchers noted. “Economic growth and increased longevity have also increased the number of people with diabetes mellitus. Recently, the public has become increasingly aware of air pollution and its harmful effects.”

They pointed out that the literature already shows that long-term exposure to PM2.5 increases the risk of developing type two diabetes, and that it’s been linked to neurological diseases as well. “In the present study, we have found that individuals living in more urbanized areas have a higher risk of developing glaucoma,” they said. “However, research in India has shown that the risk of developing closed glaucoma is higher in rural populations, while those patients with diabetes may have a higher risk of developing glaucoma. No statistical relationship has been established between air pollution and blood pressure disorders. In urban areas, open-angle glaucoma had a high prevalence due to the higher prevalence of myopia in these areas.”

The researchers concluded that while some of the effects of PM2.5 on the eye haven’t fully been explored yet, their results indicate that PM2.5 increases glaucoma risk in diabetes patients, with higher cumulative exposure posing a significantly higher risk. They advise increased awareness of the harm air pollution causes, especially in older populations and those with diabetes-associated diseases. Methods such as face masks and air purifying measures may help lower the risk of these diseases, they say.

Chiang Y, Wu S, Luo C, et al. Air pollutant particles, PM2.5, exposure and glaucoma in patients with diabetes: a national population-based nested case-control study. Intl J Environ Res Pub Health. 2021;18(18):9939.