Smoking cigarettes has long been known for its ability to damage eyesight, on top of the harm it causes to the lungs, heart, and other organs.
But a new study suggests that smoking can impair vision far earlier than is commonly thought.
Heavy smokers with an average age of 35 were markedly worse than nonsmokers at distinguishing colors as well as the contrast between shades of gray, reported the study authors, including one from Rutgers University. Previous research has linked smoking with macular degeneration and cataracts, which tend to occur decades later.
The new results, published in Psychiatry Research, do not indicate how smoking damages perception of color and contrast.
But the broad nature of the impairment suggests that it is not the result of damage to specific kinds of light-sensitive cells, such as rods or cones, said coauthor Steven Silverstein, a professor of psychiatry and ophthalmology at Rutgers Robert Wood Johnson Medical School. Instead, cigarette use likely harms a more general aspect of vision biology such as blood vessels or nerve cells.
“There is probably some more widespread problem like overall blood flow in the eye that is compromised due to all the toxic chemicals in cigarettes,” said Silverstein, who collaborated with authors from the Perception, Neuroscience and Behavior Laboratory in João Pessoa, Brazil.
Study participants included 63 people who said they smoked more than 20 cigarettes a day and scored above seven on a 10-point scale of nicotine dependence. (Points are added for “yes” answers to questions such as “Do you smoke if you are so ill you can’t get out of bed?” and “Do you find it hard to refrain from smoking in places where it is forbidden?”)
The smokers were compared with 71 healthy volunteers, defined as people who had smoked fewer than 15 cigarettes in their lives.
To measure color perception, researchers asked participants to look at various rotated images of the letter C and identify whether it was facing left, right, up, or down — a standardized exam called the Cambridge Colour Test.
Researchers altered the colors of the letter and the background to make them progressively more similar throughout the test. At a certain point, smokers had trouble telling which way the C was facing because it seemed to blend with the background, whereas nonsmokers remained able to see the letter clearly.
To determine participants’ ability to perceive shades of gray, researchers asked them to pinpoint the location of a black-and-white-striped square against a gray background. The researchers varied the thickness of the stripes as well as the degree of contrast between them, altering them to appear dark gray and light gray.