The Best and Worst Habits for Eyesight

“Are carrots good? Is blue light bad? Experts weigh in on nine common beliefs.

Oumayma Ben Tanfous for The New York Times

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If you were ever scolded as a child for reading in the dark, or if you have used blue-light-blocking glasses when working on a computer, you might have incorrect ideas about eye health.

About four in 10 adults in the United States are at high risk for vision loss, according to the Centers for Disease Control and Prevention. But many eye conditions are treatable or preventable, said Dr. Joshua Ehrlich, an assistant professor of ophthalmology and visual sciences at the University of Michigan.

Here are nine common beliefs people have about eye health, and what experts have to say about them.

Reading a book or looking at an electronic device up close is bad for your eyes.

True. Our eyes are not meant to focus on objects close to our face for long periods of time, said Dr. Xiaoying Zhu, an associate clinical professor of optometry and the lead myopia researcher at SUNY College of Optometry in New York City. When we do, especially as children, it encourages the eyeball to lengthen, which over time can cause nearsightedness, or myopia.

To help reduce the strain on your eyes, Dr. Zhu recommends following the 20-20-20 rule: After every 20 minutes of close reading, look at something at least 20 feet away for at least 20 seconds.

Reading in the dark can worsen your eyesight.

False. However, if the lighting is so dim that you need to hold your book or tablet close to your face, that can increase the risks mentioned above and create eyestrain, which can cause soreness around the eyes and temples, headache and difficulty concentrating. But these are usually temporary symptoms, Dr. Zhu said.

Spending more time outside helps eyesight.

True. Some research (mostly focused on children) suggests that outdoor time can reduce the risk of developing myopia, said Maria Liu, an associate professor of clinical optometry at the University of California, Berkeley. Experts don’t fully understand why this is, but some research suggests that bright sunlight may encourage the retina to produce dopamine, which discourages eye lengthening (though these experiments have mostly been conducted with animals, Dr. Zhu said).

Too much ultraviolet light can harm eyesight.

True. There is a reason experts say not to stare at the sun. Too much exposure to ultraviolet A and B rays in sunlight can “cause irreversible damage” to the retina, Dr. Ehrlich said. This can also increase your risk of developing cataracts, he said.

Oumayma Ben Tanfous for The New York Times

Too much UV light exposure can also increase the risk for developing cancers in the eye, Dr. Ehrlich said — though this risk is low. Wearing sunglasses, glasses or contacts that block UV rays can offer protection.

Taking a break from wearing glasses can prevent your eyesight from getting worse.

False. Some patients who need glasses tell Safal Khanal, an assistant professor in optometry and vision science at the University of Alabama at Birmingham, that they don’t wear their glasses all the time because they think it will make their condition worse. “That’s not true,” he said. If you need glasses, you should wear them.

Even a little blue light from screens is damaging to your eyes.

False. While some research has found that exposure to blue light can damage the retina and potentially cause vision problems over time, no solid evidence has confirmed that this happens with typical exposures in humans, Dr. Ehrlich said. There’s also no evidence that wearing blue-light-blocking glasses will improve eye health, he added.

But screens can be bad for eyesight in the other ways described above, including by causing dry eyes, Dr. Zhu said. “When we stare at a screen, we just don’t blink as often as we should,” she said, and that can cause eyestrain and temporary blurred vision.

Smoking is bad for eye health.

True. A 2011 C.D.C. study linked smoking with self-reported age-related eye diseases in older adults, including cataracts and age-related macular degeneration, a disease where part of the retina breaks down and blurs your vision. Toxic chemicals in cigarettes enter your bloodstream and damage sensitive tissues in the eyes including the retina, lens and macula, Dr. Khanal said.

Carrots are good for your eyes.

True. While a diet full of carrots won’t give you perfect vision, some evidence suggests that the nutrients in them are good for eye health. One large clinical trial, for instance, found that supplements containing nutrients found in carrots, including antioxidants like beta-carotene and vitamins C and E, could slow the progression of age-related macular degeneration.

Oumayma Ben Tanfous for The New York Times

Following an antioxidant-rich diet won’t necessarily prevent an eye disease from occurring, but it can be helpful “particularly for people with early macular degeneration,” Dr. Ehrlich said.

Worsening eyesight is an inevitable part of aging.

False. Most causes of declining eyesight in adulthood — including age-related macular degeneration, cataracts and glaucoma — are preventable or treatable if you catch them early, Dr. Ehrlich said. If your vision is starting to wane, don’t dismiss it as “just aging,” he added. Seeing an optometrist or ophthalmologist right away (or regularly, every year) will give you the best chance of staving off these conditions, he said.“