People are able to see because the front part of the eye bends (refracts) light and focuses it on the back surface of the eye, called the retina.
Nearsightedness occurs when there is a mismatch between the focusing power of the eye and the length of the eye. Light rays are focused in front of the retina, rather than directly on it. As a result, what you see is blurry. Most of the eye's focusing power comes from the cornea.
Nearsightedness affects males and females equally. People who have a family history of nearsightedness are more likely to develop it. Most eyes with nearsightedness are healthy, but a small number of people with severe nearsightedness develop a form of retinal degeneration.
A nearsighted person sees close-up objects clearly, but objects in the distance are blurred. Squinting will tend to make far away objects seem clearer.
Nearsightedness is often first noticed in school-aged children or teenagers. Children often cannot read the blackboard, but they can easily read a book.
Nearsightedness gets worse during the growth years. People who are nearsighted need to change glasses or contact lenses often. Nearsightedness usually stops progressing as a person stops growing in his or her early twenties.
Call for an appointment with your health care provider if your child shows these signs, which may indicate a vision problem:
Having difficulty reading the blackboard in school or signs on a wall
Holding books very close when reading
Sitting close to the television
Call for an appointment with your eye doctor if you or your child is nearsighted and experiences signs of a possible retinal tear or detachment, including:
Sudden loss of any part of the field of vision
There is no way to prevent nearsightedness. Reading and watching television do not cause nearsightedness. In the past, dilating eye drops were proposed as a treatment to slow the development of nearsightedness in children, but they have never been proven effective.
The use of glasses or contact lenses does not affect the normal progression of myopia -- they simply focus the light so the nearsighted person can see distant objects clearly. Hard contact lenses will sometimes hide the progression of nearsightedness, but vision will still get worse "under" the contact lens.
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Whitmore WG. The optics of myopia. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology Vol. 1. Philadelphia, PA: Lippincott Williams & Wilkins; 2013:chap 42.
Zadnik K, Mutti DO. Biology of the eye as an optical system. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology. Vol. 1. Philadelphia, PA: Lippincott Williams & Wilkins; 2013:chap 34.
Franklin W. Lusby, MD, ophthalmologist, Lusby Vision Institute, La Jolla, CA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.