Eye Diseases: Nearsightedness
Myopia; Shortsightedness; Refractive error - nearsightedness
Nearsightedness is when light entering the eye is focused incorrectly, making distant objects appear blurred. Nearsightedness is a type of refractive error of the eye.
If you are nearsighted, you have trouble seeing things that are far away.
Causes, incidence, and risk factors
People are able to see because the front part of the eye bends (refracts) light and points it to the back surface of the eye, called the retina.
Nearsightedness occurs when the physical length of the eye is greater than the optical length.
This makes it more difficult for the eyes to focus light directly on the retina. If the light rays are not clearly focused on the retina, the images you see may be blurry.
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 myopia 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. It usually stops progressing as a person stops growing in his or her early twenties.
Other symptoms may include:
Signs and tests
A nearsighted person can easily read the Jaeger eye chart (the chart for near reading), but has trouble reading the Snellen eye chart (the chart for distance).
A general eye examination, or standard ophthalmic exam may include:
Eye pressure measurement (See: Tonometry)...
References: Zadnik K, Mutti DO. Biology of the eye as an optical system. In: Tasman W, Jaeger EA, eds. Duane 's Ophthalmology On DVD-ROM. 1st ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2012: chap 34.
Whitmore WG, Curtin BJ. The optics of myopia. In: Tasman W, Jaeger EA, eds. Duane 's Ophthalmology On DVD-ROM. 1st ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2012: chap 42.
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