A new study points towards an association between small particle pollution and age-related macular degeneration.
An increased risk of progressive and irreversible sight loss through age-related macular degeneration (AMD) could arise from air pollution, in particular, from small particulate matter suggests a large study¹ recently conducted in the UK.
Whilst previous research had linked pollution and glaucoma, this new paper indicates that even a small rise in air pollution can trigger a rise in AMD cases. The observational study is the first to assess the connection between pollution, diagnosis of AMD, and damage in the retina.
Doctors and medical scientists have long suspected that small particle air pollution — classified as PM2.5 — could cause significant damage to the eyes when it enters the bloodstream. Whilst a 2019 study² revealed all organs can be damaged by inflammation caused by inhaled air pollution when it hits the bloodstream, the eyes receive significantly greater blood flow than other organs, thus making them potentially more vulnerable.
Currently standing at 200 million diagnosed cases and projected to reach 300 million by the year 2040 AMD is one of the major forms of irreversible eye disease, especially for the over 50s and in economically advantaged countries. Air pollution is currently not the biggest risk factor associated with AMD with genetics and poor physical health playing larger causal roles. But with lifestyles becoming healthier, the researchers believe that the weight of air pollution as a cause of AMD will increase.
It’s not all bad news, however. The authors of the study, published in the British Journal of Ophthalmology, says that its findings give doctors a new way of combating AMD. As well as pointing to new treatment options, the results of the study suggest that policy-makers must crackdown on factors that increase air pollution.
Making AMD Observations
In order to reach their conclusion, the study’s authors used data from over 100,000 individuals aged 40–69, which was collected by UK Biobank (UKBB). These participants displayed no indications of eye problems when the study began in 2006. Any formal diagnosis of AMD delivered by a medical professional to the subjects was relayed to the team.
Further to this, they assessed structural changes in the thickness of light receptors in over 52 thousand additional people using retinal imaging.
These assessments were correlated with estimates of ambient air pollution — PM2.5s, nitrogen dioxide (NO2), and nitrogen oxides (NOx) — provided by the Small Area Health Statistics Unit as part of the BioSHaRE-EU Environmental Determinants of Health Project.
Official information on traffic, industrial activity, land use, and geographical factors were used to model pollution levels in the areas immediate to participants’ homes.
The team found that from the total number of participants, over 1% — 1286 individuals — were diagnosed with AMD. Of 52,000 participants that underwent retinal imaging, 75% with a clinical diagnosis of AMD showed signs of the condition, whilst only 12% that had not received such a diagnosis showed the same effects.
When the team accounted for potentially confounding factors, lifestyles, and underlying health conditions, they concluded that PM2.5 fine particle exposure was correlated with an 8% greater risk of AMD. Apart from coarse particle pollution, all other forms of pollution were also associated with detrimental changes in retinal structure.
Building on AMD Observations
The research team that conducted the study caution about drawing conclusions from this research alone. As this was an observational study it is difficult to conclude a cause for AMD as other confounding factors could play a role in the development of the disease.
Despite these well-understood limitations, the results obtained by the team do conform to both previous research and expectations.
“Overall, our findings suggest that ambient air pollution, especially fine [particulate matter] or those of combustion-related particles, may affect AMD risk,” the authors say. “It is possible that the structural features observed may be unrelated to AMD, but associated with pollution-induced retinal toxicity.”
They add that the direction of the relationships between air pollution and both AMD and associated retinal layer thicknesses indicates higher exposure to air pollution may make the cells more vulnerable and increase the risk of AMD.
“Our findings add to the growing evidence of the damaging effects of ambient air pollution, even in the setting of relatively low exposure,” the team concludes. “If [the results] are replicated, this would support the view that air pollution is an important modifiable risk factor for AMD.”
1. Chua. S. Y. L., Warwick. A., Peto. T., et al, , ‘Association of ambient air pollution with age-related macular degeneration and retinal thickness in UK Biobank,’ British Journal of Opthalmology, [https://bjo.bmj.com/content/early/2021/01/11/bjophthalmol-2020-316218]
2. Schraufnagel. D. E., Balmes. J. R., Cowl. C. T., , ‘A Review by the Forum of International Respiratory Societies’ Environmental Committee, Part 1: The Damaging Effects of Air Pollution,’ CHEST, [DOI:https://doi.org/10.1016/j.chest.2018.10.042]