Exposure to a cadmium, a chemical in tobacco smoke, could make it more difficult for people to see in low-contrast conditions, such as low light, fog or glare, Reuters Healthreports.

Citing research led by Adam Paulsen of the University of Wisconsin, Madison, School of Medicine, which was recently published in JAMA Ophthalmology, Reuters Healthreports that higher levels of cadmium in the blood were found to be associated with diminished contrast sensitivity.

It isn’t just smokers, or those who lead what some might call unhealthy lifestyles, who are at risk for exposure to high levels of cadmium. consumption of leafy greens also can increase cadmium levels due to use of pesticides.

In addition to cadmium, cigarette smoke contains lead, which researchers also investigated for adverse impact on vision.

Both lead and cadmium accumulate in the retina. Volunteers’ contrast sensitivity was examined through an eye test. Instead of making letters smaller and smaller, researchers made successive reductions in the contrast between the letters and the background. Volunteers would start with black letters against a white background. Then, with each iteration, the letters would become more and more washed out.

At the beginning of the study, all 1,983 participants had no impairment. All were retested at five and 10 years after the study started. At the 10-year mark, nearly one quarter of the study volunteers had some impairment of their contrast sensitivity, and that impairment was associated with levels of cadmium, but not lead.

That doesn’t necessarily mean that lead won’t affect contrast sensitivity.