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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Myths About Vision

October 10, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Healthy Lifestyle
Medical Myths
Myths About Vision
Myths About Vision
Misconceptions about health and disease are remarkably common. Thus, it should come as no surprise that for something as important as vision and sight, medical myths seem particularly ubiquitous and difficult to dislodge.
Harvard Medical School Commentary

Misconceptions about health and disease are remarkably common. Thus, it should come as no surprise that for something as important as vision and sight, medical myths seem particularly ubiquitous and difficult to dislodge.

A few of the most common vision- and sight-related myths you might have heard (especially as a child) are:

  • If you cross your eyes, they may get stuck.
  • If you sit too close to the television, you'll ruin you eyesight.
  • If you try to read without enough light, you'll hurt your eyes.

Is there any truth to these adages? Although the eyes put up with a lot of use and perhaps overuse through one's lifetime, they typically respond well to stresses such as these. For example, although the muscles that control eye movement may tire if you try to keep your eyes crossed or in a particular position for a long time, no harm will come simply by trying. Similarly, you may not see well in dim light, but no part of the eye wears out or is injured if you read with a tiny penlight under the covers.

That's not to say that any of these activities are advisable. You will probably annoy those around you less by keeping your eyes in their normal alignment, will probably be more comfortable if you move back from the television while watching a show and will probably have an easier time reading in better light. Yet doing these things will not necessarily keep your eyes healthier.

These myths persist because, as with other medical myths , they seem intuitively true and were probably passed down by figures of authority. Perhaps your mother or father used such scare tactics to get you to go to sleep rather than read late into the night.

The Truth About Eye Function

For many people, the eye is complex and poorly understood, which only fuels such medical myths. The truth is simply much more interesting than fiction when it comes to sight.

You may be most surprised to learn that your eyes rely on a complicated set of muscles to function. Light enters the front of the eye through the transparent cornea and then travels through the pupil, a hole that increases in size when more light is needed and constricts in bright light. Then the light travels to the retina, which sends signals to the brain. From the retina's perspective, the pupil acts as an automatic dimmer switch. This is all thanks to tiny muscles and ligaments that flex and relax automatically.

Other specialized muscles control the shape of the lens (for focusing) and eye movements (to keep the eyes moving together). If an object is close to the eye, the muscles controlling the lens automatically change its shape to bring the object into proper focus (called accommodation). Similarly, the muscles that keep the eyes moving together (that is, they keep the eye movements conjugate) normally contract and relax in a synchronized way. You can upset this synchronicity by trying to see the tip of your nose: each inwardly turned eye sends signals to the brain that are so different than the normal signals, causing vision to "double" -- that is, the vision sees two disparate images that cannot be readily integrated into one.

Fortunately, these tiny muscles that control eye function are like other muscles in the body: they may fatigue, but they are resilient. Your body, including your eyes, evolved to handle a lot of daily wear and tear. So if you are one of those skeptics who doubts that crossing your eyes, sitting close to a television or reading in dim light is really harmful, you are seeing it all quite clearly.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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