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exotropia
Exotropia (from Greek εξοτρὀπια, εξο "exo" meaning "to exit" or "move out of" and τρὀπειν "tropein" meaning "to turn"),〔(【引用サイトリンク】title=''Exotropia'' Origin )〕 also referred to as ''divergent squint'', is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision. Infantile exotropia (sometimes called "congenital exotropia") is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.
The brain's ability to see three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and aimed at the same target, the visual portion of the brain fuses the forms into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. This causes loss of depth perception and binocular vision. There have also been some reports of people that can "control" their nonfunctioning eye.
==Causes==
The causes of exotropia are not fully understood. There are six muscles that control eye movement, four that move the eye up and down and two that move it side to side. All these muscles must be coordinated and working properly in order for the brain to see a single image. When one or more of these muscles doesn't work properly, some form of strabismus may occur. Strabismus is more common in children with disorders that affect the brain such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors. One study has found that children with exotropia are three times more likely to develop a psychiatric disorder in comparison with the general population.〔Mayo Clinic. "(Eye Divergence In Children Triples Risk Of Mental Illness )." ScienceDaily 28 November 2008. 30 November 2008〕〔McKenzie J, et al "Prevalence and sex differences of psychiatric disorders in young adults who had intermittent exotropia as children" Arch Ophthalmol 2009; 127:743-47.()〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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