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.
Symptoms
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.
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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:
Eyestrain
Headaches (uncommon)
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)
Refraction test, to determine the correct prescription for glasses
Retinal examination
Slit-lamp exam of the structures at the front of the eyes
Test of color vision, to look for possible color blindness
Tests of the muscles that move the eyes
Visual acuity, both at a distance (Snellen), and close up (Jaeger)
Treatment
Wearing eyeglasses or contact lenses can help shift the focus of the light image directly onto the retina, producing a clearer image.
The most common surgery to correct myopia is LASIK. An excimer laser is used to reshape (flatten) the cornea, shifting the focus.
Expectations (prognosis)
Early diagnosis of nearsightedness is important, because a child can suffer socially and educationally by not being able to see well at a distance.
Complications
Complications can occur in people who use contact lenses (corneal ulcers and infections)
Complications of laser vision correction are uncommon, but can be serious
People with myopia can, in rare cases, develop retinal detachments or retinal degeneration
Calling your health care provider
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:
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Flashing lights
Floating spots
Sudden loss of any part of the field of vision
Prevention
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.
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.
