Several environmental factors were shown to influence AMD risk in this study, including ozone, geographic latitude and pollution. Photo: Federico Respini, Marcin Jozwiak. Click image to enlarge.

Coupling patient-level information from the IRIS Registry with environmental data has provided a unique opportunity to investigate whether natural factors contribute to AMD. A recent analysis revealed significant associations between several environmental variables and the risk of active exudative AMD, including latitude, solar irradiance and pollution. Notably, the strongest environmental associations differed between AMD subgroups.

The researchers included 9,884,527 patients older than 55 and categorized them as non-exudative, inactive exudative, active exudative or unaffected. Elevation, latitude, solar irradiance measured in global horizontal irradiance and direct normal irradiance, temperature, precipitation and pollution were included in the study’s models.

Statistically significant associations with active exudative AMD were global horizontal radiation (OR: 3.848), direct normal irradiance (OR: 0.58), latitude (OR: 1.11), ozone (OR: 1.01) and nitrogen dioxide (OR: 1.00). The only significant environmental associations with any AMD were inches of snow in the winter (OR: 1.00) and ozone (OR: 1.01).

“Our findings reveal previously unappreciated associations between environmental factors and disease progression in AMD,” the researchers wrote in their paper for the Ophthalmology journal. “The development of exudative AMD from non-exudative AMD represents a clear progression in disease severity, and thus motivates the distinction between exudative and non-exudative forms of AMD.”

The team noted that separating solar irradiance into global horizontal irradiance (direct and scatter irradiance) vs. direct-only irradiance revealed that these distinct classes of sunlight had opposing associations with the risk of developing active exudative AMD.

They noted that global horizontal irradiance may better indicate the irradiance incident on the human retina. “Human eyes are situated to naturally view the horizon, and typically the light incident on the retina is scatter irradiance, rather than light directly from the solar disc,” the researchers wrote. “Thus, higher global horizontal irradiance may increase AMD risk because it indicates the amount of incident light on the retina.”

One thing to keep in mind is that, due to the retrospective and associational nature of the study, causal effects of environmental influences on AMD development cannot be established.

Nevertheless, the team concluded, “This study advances the understanding of environmental influences on AMD risk at different stages of the disease, highlighting associations between latitude, solar irradiance and pollution in active exudative AMD.”

Hunt MS, Chee YE, Saraf SS, et al. Association of environmental factors with age-related macular degeneration using the Intelligent Research in Sight Registry. Ophthalmology. July 11, 2022. [Epub ahead of print].