UV rays, eye rubbing and atopy (type 1 hypersensitive response) are three known risk factors for keratoconus. Researchers recently investigated if pollution, whose role in the physiopathology of keratoconus is unclear, should be added to that list.

A correlation study was performed to determine the influence of pollution on keratoconus. The study looked at environmental levels of fine particulate matter (PM) at sizes of 2.5µm and 10µm, as these are most frequently involved during pollution peaks and correlate with prevalence in World Health Organization (WHO) epidemiological studies, the researchers explained in their paper.

The team compared WHO data from 2012 to 2016 with a literature review of 24 journal articles on keratoconus prevalence. Statistical analysis showed a moderate correlation between prevalence of keratoconus and the levels of PM_2.5 and a strong correlation with the levels of PM₁₀. This study shows a correlation between the rate of fine particles and the prevalence of keratoconus, they concluded.

“Patients’ cornea with keratoconus could be particularly sensitive to the accumulation of reactive oxygen species and that process could be favored by a dysfunction of antioxidant mechanisms,” the authors noted in their study. “In the long-term, the pollution could increase the rate of cell death and cause a degradation process of the extracellular matrix leading to corneal thinning.” The impact, they speculated, could be greater in keratoconic eyes than in healthy corneas. “This could induce the development of keratoconus in genetically susceptible individuals and aggravate its evolution when already present.”

The authors noted their analysis was solely on two types of fine particles, not other substances in the atmosphere such as metals, gases, soot and nanoparticles.

“Pollution seems to be an important new factor for understanding the disease’s evolution or appearance on predisposed terrain,” the authors concluded. “This factor could promote existing risk factors (eye rubbing and atopy). It also has its own effects: cytotoxic effects, disturbance of cell function (senescence) and increased apoptosis caused by particles would constitute a direct effect of pollution on the cornea. In the stroma, nanoparticles could be able to integrate into the structure of collagen fibrils,” theoretically disrupting the structure and function of the stroma.