This is called, Amblyopia, a disorder of sight. It’s a decreased vision in an eye that otherwise appears normal, or out of proportion. In amblyopia, visual stimulation either fails to be or is poorly transmitted through the optic nerve to the brain for a continuous period of time. It can also occur when the brain "turns off" the visual processing of one eye to prevent double-vision, for example in strabismus (crossed eyes).
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Signs and symptoms
People who have severe amblyopia may experience related visual disorders, most notably poor depth perception.
Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity (VA), contrast sensitivity function (CSF), and vernier acuity as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. People with amblyopia also have problems of binocular vision such as limited stereoscopic depth perception and usually have difficulty seeing the three-dimensional images in hidden stereoscopic displays such as autostereograms. However, perception of depth from monocular cues such as size, perspective, and motion parallax remains normal.
Three main causes of amblyopia
Strabismic: by strabismus (misaligned eyes) usually results in normal vision in the preferred sighting eye (the eye that the person prefers to use), but may cause abnormal vision in the deviating or strabismus eye due to the difference between the images projecting to the brain from the two eyes it causes double vision (diplopia), since the two eyes are not fixed on the same object these tend to show ocular motion deficits when reading, they tend to make more saccades per line than persons with normal stereo vision, and to have a smaller reading speed, especially when reading a text with small font size.
Refractive: by anisometropia (high degrees of nearsightedness, farsightedness, or astigmatism in one or both eyes), Refractive or anisometropic amblyopia may result from anisometropia (unequal refractive error between the two eyes). Anisometropia exists when there is a difference in the power between the two eyes. The eye which provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system.
Deprivational: by deprivation of vision early in life by vision-obstructing disorders such as congenital cataract. Deprivation and occlusion amblyopia results when the ocular media become opaque, such as is the case with congenital cataract or corneal haziness. These opacities prevent adequate visual input from reaching the eye, and therefore disrupt development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the eyelid (ptosis) or some other problem causes the upper eyelid to physically occlude a vision, which may cause amblyopia quickly. Occlusion amblyopia may be a complication of a hemangioma that blocks some or the entire eye.
A lazy eye (amblyopia) is often diagnosed and treated by an orthoptist under the supervision of an ophthalmologist.
The two main treatment options for a lazy eye are:
Encouraging the use of the affected eye so that vision can develop properly.
Glasses Vision problems such as short- or long-sightedness can be corrected using glasses. Glasses may also help to straighten a squint, and in some cases can fix the lazy eye without the need for further treatment.
Source:
http://en.m.wikipedia.org/
http://www.nhs.uk/Conditions/
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