NEW YORK – 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 (CDC). But many eye conditions are treatable or preventable, says 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.

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

True. The eyes are not meant to focus on objects close to one’s face for long periods of time, says Dr Zhu Xiaoying, an associate clinical professor of optometry and the lead myopia researcher at the State University of New York College of Optometry in New York City.

When they do, especially as children, it encourages the eyeball to lengthen, which over time can cause near-sightedness, 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 ft (about 6m) away for at least 20 seconds.

2. 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 eye strain, which can cause soreness around the eyes and temples, headache and difficulty concentrating. But these are usually temporary symptoms, Dr Zhu says.

3. Spending more time outside helps eyesight

True. Some research (mostly focused on children) suggests that outdoor time can reduce the risk of developing myopia, says clinical optometry associate professor Maria Liu at the University of California, Berkeley.

Experts do not fully understand why this is, but some research suggests that bright sunlight may encourage the retina to produce dopamine, which discourages eye lengthening (although these experiments have mostly been conducted with animals, Dr Zhu says).

4. Too much ultraviolet (UV) 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 says. This can also increase your risk of developing cataracts, he adds.

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

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

False. Some patients who need glasses tell optometry and vision science assistant professor Safal Khanal, who is from the University of Alabama at Birmingham, that they do not wear their glasses all the time because they think it will make their condition worse. “That’s not true,” he says.

If you need glasses, you should wear them.

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

False. Although 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, says Dr Ehrlich. There is 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 says.

“When we stare at a screen, we just don’t blink as often as we should,” she says, and that can cause eye strain and temporary blurred vision.

7. Smoking is bad for eye health

True. A 2011 CDC 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 the vision.

Toxic chemicals in cigarettes enter your bloodstream and damage sensitive tissues in the eyes, including the retina, lens and macula, says Prof Khanal.

8. Carrots are good for your eyes

True. Although a diet full of carrots will not 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 with nutrients found in carrots, including antioxidants such as beta-carotene and vitamins C and E, could slow the progression of age-related macular degeneration.

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

9. Worsening eyesight is an inevitable part of ageing

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 says.

If your vision is starting to wane, do not dismiss it as “just ageing”, he adds.

Seeing an optometrist or ophthalmologist right away (or regularly, every year) will give you the best chance of staving off these conditions, he says. NYTIMES