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Strabismus, also known as "heterotropia", "squint", "crossed eye", "cockeyed', "wandering eye", or "wall eyed", is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles which prevents bringing the gaze of each eye to the same point in space, preventing proper binocular vision, which may adversely affect depth perception. Strabismus can be either a disorder of the brain coordinating the eyes, or a disorder of one or more muscles, as in any process that causes a dysfunction of the usual direction and power of the muscle or muscles.
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Classification
The misalignment of the eyes in strabismus can be classified in many different ways:
Involvement of accommodative system
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Direction
Strabismus may be classified as convergent, divergent, or vertical based on the direction of the deviating eye.
Convergent strabismus, also known as esotropia, is strabismus in which the deviating eye turns inward, so that its foveal line of sight crosses the line of sight of the fixating eye at a point nearer than the object of fixation.[Cline D; Hofstetter HW; Griffin JR. Dictionary of Visual Science. 4th ed. Butterworth-Heinemann, Boston 1997. ISBN 0-7506-9895-0]
Divergent strabismus, also known as exotropia, is strabismus in which the deviating eye turns outward, so that its foveal line of sight crosses the line of sight of the fixating eye at a point beyond the object of fixation or at a hypothetical point behind the eyes.
Vertical strabismus is strabismus in which the deviating eye is turned either up or down.[ Hypertropia is strabismus characterized by the upward deviation of the line of sight of the non-fixating eye with reference to that of the fixating eye.][ Hypotropia is strabismus characterized by the downward deviation of the line of sight of the non-fixating eye with reference to that of the fixating eye.][ ]
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Concomintance
Strabismus may be classified based on whether the deviation remains equal or varies with the direction of gaze (i.e. concomitance).
Concomitant strabismus is strabismus in which the angle of deviation remains constant for all directions of gaze and with either eye fixating.[ This indicates that the individual extraocular muscles function individually, but that they may simply not be aimed at the same target. Concomitant strabismus in a child under the age of 6 rarely indicates serious neurologic disorder. Blindness in one eye usually causes concomitant strabismus, with the eye of a child turning inward, and that of an adult turning outward.]
Nonconcomitant strabismus is strabismus in which the angle of deviation varies with the direction of gaze and/or with the eye that fixates.[ It is due to paralysis or paresis of one or more of the extraocular muscles.][ This indicates that one or more of the extraocular muscles may not be functioning normally.]
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Frequency
Strabismus may be classified based on how frequently it is present.
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Involvement of accommodative system
Strabismus may be classified based on whether it is affected by accommodation.
Accommodative strabismus is strabismus that results from abnormal demand on accommodation, such as convergent strabismus resulting from uncorrected hyperopia or divergent strabismus resulting from uncorrected myopia.
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Differential diagnosis: pseudostrabismus
Pseudostrabismus is the false appearance of strabismus. It generally occurs in infants and toddlers whose bridge of their nose is wide and flat. This causes the appearance of strabismus. With age the bridge of the child's nose will narrow and the folds in the corner of the eyes will go away. To detect the difference between pseudostrabismus and strabismus, a flashlight is shone in the child's eyes. When the child is looking at the light a reflection can be seen on the front surface of the pupil. If the eyes are properly aligned with one another then the reflection will be in the same spot of each eye. If strabismus is present, then the reflection from the light will not be in the same spot of each eye.
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Diagnosis
During eye examinations, ophthalmologists and optometrists typically use a cover test to aid in the diagnosis of strabismus. If the eye being tested is the strabismic eye, then it will fixate on the object after the "good" eye is covered, as long as the vision in this eye is good enough.
If it is the "good" eye, there will be no change in fixation, as it is already fixated.
Depending on the direction that the strabismic eye deviates, the type of tropia or phoria may be assessed.
A simple screen for strabismus is the Hirschberg test.
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Treatment and management
As with other binocular vision disorders, the primary therapeutic goal for those with strabismus is comfortable, single, clear, normal binocular vision at all distances and directions of gaze.
If minor and detected early, amblyopia can often be corrected with use of an eyepatch on the dominant eye and/or vision therapy. The use of eyepatches is unlikely to change the angle of strabismus. Advanced strabismus is usually treated with a combination of eyeglasses or prisms, vision therapy, and surgery, depending on the underlying reason for the misalignment. Surgery attempts to align the eyes by shortening, lengthening, or changing the position of one or more of the extraocular eye muscles, and is frequently the only way to achieve cosmetic improvement. Glasses affect the position by changing the person's reaction to focusing. Prisms change the way light, and therefore images, strike the eye, simulating a change in the eye position.
Early treatment of strabismus and/or amblyopia in infancy can reduce the chance of developing amblyopia and depth perception problems. Eyes that remain misaligned can still develop visual problems. Although not a cure for strabismus, prism lenses can also be used to provide some comfort for sufferers and to prevent double vision from occurring.
In adults with previously normal alignment, the onset of strabismus usually results in double vision (diplopia).
Advocates of the Bates method assert that it can reverse strabismus.
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Prognosis
When strabismus is congenital or develops in infancy, it can cause amblyopia, in which the brain ignores input from the deviated eye. Both strabismus and amblyopia are sometimes referred to as lazy eye. The appearance of strabismus may also be a cosmetic problem. One study reported that 85% of adult strabismus patients "reported that they had problems with work, school and sports because of their strabismus". The same study also reported that 70% said strabismus "had a negative effect on their self-image".
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People with strabismus
The Italian painter Giovanni Francesco Barbieri (1591-1666) was known as Il Guercino, meaning, in Italian, "The Squinter," a nickname that was given to him because he was cross-eyed.
Kate Moss and Harry Chapin (and his son) are examples of a celebrities with a easily recognized amount of strabismus.
Marty Feldman had strabimus, accompanied by exophthalmos (his eyes also bulged).
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Wikibook
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See also
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