Smoking or living with cigarette smoke can accelerate age-related degeneration of the eyes, researchers from Johns Hopkins Medicine found, and it hurts young eyes more.

“Smoking is often assumed to accelerate aging by releasing tissue-damaging molecules called free radicals,” Dr. James T. Handa, principal investigator and chief of the retina division of the Wilmer Eye Institute, said in a press release. “We saw the expression of aging genes linked to mitochondrial function, [protein stability], [cellular self-cleanup], inflammation and metabolism.”

Aside from lung cancer, it has long been known that smoking can cause disease, death and disability. The Centers for Disease Control and Prevention reports that more than 16 million Americans live with a smoking-related disease. Smokers are four times more likely to suffer loss of vision and blindness, according to the Food and Drug Administration.

The exact cause has not been known, until now.

The Hopkins research revealed how smoking harms the eye by observing genetic expression — non-permanent shifts in the way cells use segments of DNA. These changes in expression harm cells in the eye directly, as well as impair their ability to respond to environmental stresses.

Then they compared their mouse observations to retinal tissue from organ donors who smoked and those who did not. They found that cigarette smoke increased or decreased the expression of the same 1,698 genes in the eyes of both humans and mice.

The National Institutes of Health funded the research, published in the Proceedings of the National Academy of Sciences in January.

A separate Hopkins study funded by the FDA and National Heart, Lung, and Blood Institute adds to evidence that “cutting back” on smoking does little to reduce the damage. Quitting entirely is the most effective way to improve future health, they found.

“This study shows that even low levels of smoking — for example, only a few cigarettes a day — carry substantial cardiovascular risks,” Dr. Michael Blaha, director of clinical research for the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease and the study’s corresponding author, said on the Hopkins website. “Quitting completely — not just cutting back — provides the greatest health benefit.”

They reviewed data from 22 studies following more than 300,000 adults for almost 20 years. They found 125,000 deaths and 54,000 heart attacks or other events.

They also developed a risk index based on the number of cigarettes per day, how long someone smoked, and how long it has been since they quit smoking.

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