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Why Are You Nearsighted? Here's an Explanation You May Not Have Heard


Story at-a-glance -

  • Higher levels of total time spent outdoors are associated with less nearsightedness in children
  • Outdoor light helps you maintain proper vitamin D levels, which supports the function of muscle tissue around the lens in your eye
  • Outdoor light exposure triggers the release of dopamine, a neurotransmitter that slows down growth of the eye and perhaps stops the elongation of the eye during development

By Dr. Mercola

Nearsightedness, also known as myopia, is a vision problem in which close objects appear clear but distant objects appear blurry. This condition is said to be caused by refractive errors. Refraction is the bending of light as it passes through one object to another.

When light rays are refracted through your eye’s cornea and lens, they become focused on the retina, which then “converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see,” as stated by the National Eye Institute.1

Refractive errors occur when the shape of your eye prevents light from focusing on your retina. This is caused by changes in the shape of your eye (such as the length of your eyeball or shape of your cornea) or aging of the lens.

Nearsightedness is incredibly common, affecting up to 40 percent of Americans and up to 90 percent of young adults in Asian countries.2 It’s estimated that up to one-third of the world’s population may be nearsighted by the end of the decade – that’s 2.5 billion people.3

Why some people develop refractive errors and others don’t is unknown, but there’s an emerging theory that spending too much time indoors may be to blame.

Your Eyes May Need Time Outside to Stay Healthy

It was once suggested that an excess of close bookwork could lead to nearsightedness, by altering growth and shape of the eyeball. This theory came about centuries ago when a German astronomer by the name of Johannes Kepler stated that his studies caused his nearsightedness.

The theory seemed plausible, especially as rates of the condition skyrocketed in regions like Shanghai, where teens spend about 14 hours a week on homework (compared to about six in the US).4

A strong association has also been found between rates of nearsightedness and increasing educational pressures. However, the bookwork theory was missing one crucial aspect.

When researchers looked at number of books read per week or hours spent using a computer, no significant link to nearsightedness was found.5 What did have a significant association, however, was the number of hours spend playing sports or engaging in other outdoor activity.6

This was found in 2006 and again in 2007, when researchers found that higher levels of total time spent outdoors were associated with less nearsightedness in children.7 As reported in Nature:8

“[Researchers] tried to eliminate any other explanations for this link — for example, that children outdoors were engaged in more physical activity and that this was having the beneficial effect.

But time engaged in indoor sports had no such protective association; and time outdoors did, whether children had played sports, attended picnics, or simply read on the beach. And children who spent more time outside were not necessarily spending less time with books, screens, and close work.

“We had these children who were doing both activities at very high levels and they didn't become myopic,” says [researcher Kathryn] Rose. Close work might still have some effect, but what seemed to matter most was the eye's exposure to bright light.”

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How Does Outdoor Light Affect Your Vision?

Spending time outdoors offers exposure to multiple types of light, including ultraviolet B rays (UVB, which leads to the production of vitamin D) and visible bright light.

Research shows that people with nearsightedness have lower blood levels of vitamin D,9 which supports the function of muscle tissue around the lens in your eye. According to the Ohio State University College of Optometry:10

This muscle not only helps focus light on the retina, but may also maintain the proper eye shape and length between the lens and the retina, something that can become distorted during the rapid growth of a child’s eye.”

It might also be that vitamin D levels are a marker for time spent outside, and outdoor light is known to have beneficial effects beyond vitamin D production.

When exposed to outdoor light, for instance, cells in your retina trigger the release of dopamine, a neurotransmitter that slows down growth of the eye and perhaps stops the elongation of the eye during development.


Retinal dopamine is normally produced on a diurnal cycle — ramping up during the day — and it tells the eye to switch from rod-based, nighttime vision to cone-based, daytime vision.

Researchers now suspect that under dim (typically indoor) lighting, the cycle is disrupted, with consequences for eye growth.

‘If our system does not get a strong enough diurnal rhythm, things go out of control,’ says [researcher Regan] Ashby, who is now at the University of Canberra. ‘The system starts to get a bit noisy and noisy means that it just grows in its own irregular fashion.’

Three Hours Outside a Day May Help Protect Children’s Eyes

As for how much time outdoors is necessary for eye health, research by researcher Ian Morgan of the Australian National University, suggests three hours per day with light levels of at least 10,000 lux may protect children from nearsightedness.12

This is the amount of light you would be exposed to on a bright summer day. An indoor classroom, by comparision, would only provide about 500 lux. It seems clear that the more time children spend outdoors, the lower their risk of nearsightedness becomes.

At a school in Taiwan, for instance, when children began spending their 80-minute daily break outdoors rates of myopia diagnosis dropped to 8 percent compared to 18 percent at a nearby school.13 And as reported by Ohio State University:14

"Data suggest that a child who is genetically predisposed to myopia is three times less likely to need glasses if they spend more than 14 hours a week outdoors," says Optometrist Donald Mutti, OD, PhD, of The Ohio State University College of Optometry."

In Singapore, public health campaigns have even been introduced encouraging children to get outdoors to prevent nearsightedness. The slogan? “Keep myopia away, go outdoors and play!”15

Why I Rarely Wear Sunglasses

I only wear sunglasses on rare occasions, such as when I'm skiing or, sometimes, if I'm boating on the water. Under these conditions, the snow or water greatly magnifies the sunlight, which could potentially be harmful, especially after hours of exposure.

On an average sunny day, however, wearing sunglasses is the last thing you want to do for your vision health, because you will be blocking potentially beneficial wavelengths of light from reaching your eyes. There are actually more than 1,500 wavelengths of light that you need to nourish your eyes.

So I avoid using sunglasses, because I believe your eyes need to receive the full spectrum of light to function optimally, and sunglasses block out some essential waves of the light spectrum.

Instead of sunglasses, I wear a lightweight cap with a visor like this one to protect my face and eyes from direct sunlight. This is typically all that is needed and will still allow your eyes to benefit from the full spectrum of light.

Eyes’ Exposure to Bright Light Is Important for Overall Health

There's another reason beyond vision health why you need to be careful about overly shielding your eyes from sunlight, and that is because when full-spectrum light enters your eyes, it not only goes to your visual centers enabling you to see, but also goes to your brain's hypothalamus where it impacts your entire body.

Your hypothalamus controls body temperature, hunger and thirst, water balance, and blood pressure. Additionally, it controls your body's master gland, the pituitary, which secretes many essential hormones, including those that influence your mood. Exposure to full-spectrum lighting is actually one effective therapy used for treating depression, infection, and much more.

Studies have also shown that poor lighting in the workplace triggers headaches, stress, fatigue, and strained watery eyes, not to mention inferior work production. Conversely, companies that have switched to full-spectrum lights report improved employee morale, greater productivity, reduced errors, and decreased absenteeism.

Some experts even believe that "malillumination" is to light what malnutrition is to food. Your “body clock” is also housed in tiny centers located in the hypothalamus, controlling your body's circadian rhythm. This light-sensitive rhythm is dependent on Mother Nature, with its natural cycles of light and darkness, to function optimally.

Consequently, anything that disrupts these rhythms, like inadequate sunlight exposure to your body (including your eyes), has a far-reaching impact on your body's ability to function. The best way to get exposure to healthy full-spectrum light is to do it the way nature intended, by going out in the sun with your bare skin – and “bare” eyes -- exposed on a regular basis.

Your Diet May Be Another Factor in Nearsightedness

Exposure to outdoor light is likely only one factor that plays a role in the development of nearsightedness. Your diet is likely another. Studies carried out in hunter-gatherer societies and in recently westernized hunter-gatherer groups indicate that myopia normally occurs in 0 to 2 percent of the population, and that moderate to high myopia is either non-existent or occurs in about one person out of 1,000.

Sugar and diets high in refined starches such as breads and cereals increase your insulin levels. This affects the development of your eyeball, making it abnormally long and causing near-sightedness, according to Evolutionary Biologist Loren Cordain, at the Colorado State University in Fort Collins.16 Cordain found that when these hunter-gatherer societies change their lifestyles and introduce grains and carbohydrates, they rapidly develop (within a single generation) myopia rates that equal or exceed those in western societies.

The reason for this is because high insulin levels from excess carbohydrates can disturb the delicate choreography that normally coordinates eyeball lengthening and lens growth. And if the eyeball grows too long, the lens can no longer flatten itself enough to focus a sharp image on the retina. Hunter-gatherer diets are typically characterized by high levels of protein, moderate levels of fat, and low levels of carbohydrates compared to modern western diets.

Additionally, the carbohydrates present in hunter-gatherer diets are of a low glycemic index, meaning they are absorbed slowly, producing a gradual and minimal rise in blood sugar and insulin levels when compared to the sugars and refined starches in western diets.

This theory is also consistent with observations that you’re more likely to develop myopia if you are overweight or have adult-onset diabetes, both of which involve elevated insulin levels. Following my nutrition plan will automatically reduce, or eliminate, excess sugar and grain intake from your diet.

Are You Nearsighted? Try the Bates Method

According to Greg Marsh, a certified natural vision coach, clear vision is achievable, even if you’re already wearing strong corrective lenses. The method Greg teaches was initially conceived by Dr. William H. Bates, over 100 years ago.

A board-certified ophthalmologist at the top of his field, Dr. Bates taught his method to many, and it was so effective that it ended up being banned in New York after the optometrists lobbied the local politicians! So how does the Bates Method work? Greg explains:

"Basically, there are six muscles on the outside of your eye, and they're moving it around... Ideally, these muscles are easily following visual interests... The problem is – it could be for emotional reasons, physical stress, or whatever – you start to strain. Once you start to strain, your vision starts to go."

The action of straining essentially squeezes your eyeballs, contorting them. This makes your vision blurry, as it alters where the field of vision "lands" on your retina. Now you have three basic choices:

  1. Find out what's stressing you, making you strain. Let it go, relax, and get your vision back. Dr. Bates developed ingenious tools for doing just that
  2. Get laser in-situ keratomileusis (LASIK), which permanently alters your focal length
  3. Get corrective lenses. The problem with corrective lenses is that now you're creating permanent strain

The Bates Method isn't really an exercise; it's more of a mental approach. It's also worth noting that the Bates Method is clearly NOT a medical approach. You still need to see your regular eye doctor for checkups. One of the most famous Bates Method techniques is palming. Look around and notice the level of clarity of your vision at present.

Then, simply place the center of your palms over your eyes. Relax your shoulders. You may want to lean forward onto a table or a stack of pillows, to facilitate relaxation. Relax like this for at least two minutes. Then remove your hands, open your eyes, and notice whether anything looks clearer. Usually, it will.

The Bates Method is really quite simple, yet it requires patience, and some finesse. Remember, the goal is not to “train” or exercise your eyes to make them stronger. The goal is to relax them. Greg’s program provides thorough instructions that can help you get there. Also, remember that your mindset is important. With faith in yourself and your body’s self-regenerative ability, the toughest hurdle is learning to relax, so your eyes can function in accord with their natural design.