Smoking a pack of cigarettes a day can pose threats to your health, including your vision. That’s the upshot of recent findings by a Rutgers University researcher, who noted significant changes in color vision among heavy smokers.

The study included 63 people who smoked at least 20 cigarettes a day and 71 others who had smoked less than a pack of cigarettes in their lives. The participants were 25 to 45 years old and had normal or corrected vision.

Both groups were tested for vision contrast and their ability to distinguish colors while observing images on a monitor from nearly five feet away. The smokers had significant changes in blue-yellow and red-red green color perception compared with those who had smoked only a handful of cigarettes or less. The heavy smokers also had a diminished ability to distinguish contrast, which are subtle differences in brightness.

The findings suggest that substances with neurotoxic chemicals like those in cigarettes may lead to an overall loss of color vision. That may be because cigarette smoking has been associated with effects on areas of the brain that help to process vision.

This is not the first study to associate smoking with vision issues. Other researchers have shown that long-term smoking can turn the eye’s lens yellow and double the risk of macular degeneration, a disease that causes irreversible vision loss.

The recent findings didn’t establish a definite physiological basis for smoking’s effect on vision, but some evidence suggests that tobacco use may damage the eye’s retina.

For the 34.3 million smokers in the United States, vision damage is yet another reason to consider quitting.