Cadmium exposure may increase the risk for problems with a key component of good vision, according to a new study from the University of Wisconsin School of Medicine and Public Health.

The study, “Association of Cadmium and Lead Exposure with Incidence of Contrast Sensitivity Impairment Among Middle-Aged Adults,” was published in JAMA Ophthalmology. Adam Paulsen, researcher with the Department of Ophthalmology and Visual Sciences, is the lead researcher on the study.

The study looked at contrast sensitivity, a measure of how well someone sees an image against a background. Common low-contrast conditions include low light, fog or glare. Cadmium and lead are both neurotoxic heavy meals. Cadmium exposure typically happens through inhaling cigarette smoke or eating green leafy vegetables (cadmium can be found in soil), rice and shellfish. People are usually exposed to lead by polluted air, old lead-based paint or water pipes.

The study analyzed data from the long-term population-based Beaver Dam Offspring Study, a large ongoing study of aging adults in Beaver Dam, Wisconsin. Nearly 2,000 male and female adults who were free of contrast-sensitivity problems provided baseline data and then had follow-up exams, including blood tests and eye screenings, at five-year intervals. Data were collected from 2005 to 2017 and the participants ranged in age from 21 to 84 with a mean age of 48 at baseline.

Ten years after the beginning of the study, 24.8 percent of the participants had developed an impaired ability to see contrast, and higher incidence was linked to higher levels of cadmium exposure. Lead levels were not associated with higher risk of contrast sensitivity impairment. The incidence of the impairment was highest in the 65-to-84 age group. More than 87 percent of the cases occurred in participants whose visual acuity was no worse than 20/40 at any time.

“Contrast sensitivity is understudied, but it is an important part of your vision. It can impact daily life with increasing difficulty for near-vision tasks, like reading small print, inserting keys into locks and night driving, even if you have appropriately corrected visual acuity,” said Paulsen. “This study is important because it shows some of the risk may be somewhat preventable. For example, not smoking could make a difference to keep good vision, longer.”

Paulsen also says due to the design of the study, it could not pinpoint the exact mechanism by which cadmium might produce these problems.

Dr. Karen Cruickshanks, PhD, professor of ophthalmology and visual sciences and population health sciences, is the principal investigator of the study. Carla Schubert, researcher in the Department of Ophthalmology and Visual Sciences, was the second author.