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Strabismus
From Wikipedia, the free encyclopedia
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| Strabismus prevents bringing the gaze of both eyes to the same point in space | |
| ICD-10 | H49. - H50. |
| ICD-9 | 378 |
| OMIM | 185100 |
| DiseasesDB | 29577 |
| MedlinePlus | 001004 |
| MeSH | D013285 |
Strabismus (from Greek: στραβισμός strabismos, from στραβίζειν strabizein "to squint," from στραβός strabos "squinting, squint-eyed"[1]) is a condition in which the eyes are not properly aligned with each other.[2] It typically involves a lack of coordination between the extraocular muscles that prevents bringing the gaze of each eye to the same point in space and 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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During eye examinations, ophthalmologists, orthoptists, 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 the "good" eye is being tested, there will be no change in fixation, as it is already fixated. Depending on the direction that the strabismic eye deviates, the direction of deviation may be assessed. Exotropic is outwards (away from the midline) and esotropic is inwards (towards the nose).
A simple screening test for strabismus is the Hirschberg test. A flashlight is shone in the patient's eye. When the patient 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, the reflection will be in the same spot of each eye. Therefore, if strabismus is present, the reflection from the light will not be in the same spot of each eye.
Strabismus may be classified as unilateral, bilateral, or alternating based on whether one eye or both eyes are affected. A unilateral strabismus will consistently have the same eye 'wandering'. Bilateral strabismus is a condition where both eyes are squinting at the same time; either convergently or divergently (both are subtypes of Concomitant strabismus). Finally, an alternating strabismic patient can fixate on a target object with either eye. In this case either eye may be askew while the opposite eye is focused on the target. The cover-uncover test is used to diagnose various types of tropias, which is a medical term for strabismus.[2]
Strabismus may also be classified based on time of onset, either congenital or acquired.[2]
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.[3]
Whereas amblyopia, if minor and detected early, 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).
In his book Perfect Sight without Glasses, maverick ophthalmologist William Bates advocated relaxation and thinking relaxing thoughts as a way to reduce strabismus: "When the disturbing thought is replaced by one that relaxes, the squint disappears, the double vision and the errors of refraction are corrected; and this is as true of abnormalities of long standing as of those produced voluntarily." Bates was of the opinion that the cause of "squint, or of any other functional disturbance of the eye" was simply "wrong thoughts" and these "wrong thoughts" (and therefore the resulting pathology of the visual system) could be cured by relaxing thoughts. "In a fraction of a second the highest degrees of refractive error may be corrected, a squint may disappear, or the blindness of amblyopia may be relieved. If the relaxation is only momentary, the correction is momentary. When it becomes permanent, the correction is permanent."[4]
The mainstream medical community regards the Bates method with skepticism.[5] However, advocates continue to make the assertion that it can reverse strabismus.[6]
When strabismus is congenital or develops in infancy, it can cause amblyopia, in which the brain ignores input from the deviated eye. Strabismus can lead to a permanent weakening of vision in the strabismic eye called amblyopia 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."[7]
Pseudostrabismus is the false appearance of strabismus. It generally occurs in infants and toddlers whose bridge of the nose is wide and flat, causing the appearance of strabismus. With age, the bridge of the child's nose narrows and the folds in the corner of the eyes go away. To detect the difference between pseudostrabismus and strabismus, a Hirschberg test may be used.
Strabismus can be an indication that a cranial nerve has a lesion. Particularly Cranial Nerve III (Occulomotor), Cranial Nerve IV (Trochlear) or Cranial Nerve VI (Abducens). A strabismus caused by a lesion in either of these nerves results in the lack of innervation to eye muscles and results in a change of eye position. A strabismus may be a sign of increased intracranial pressure, as CN III is particularly vulnerable to damage from brain swelling.
More commonly however, squints are termed concominant (i.e. non paralytic). This mean the squint is not caused by a leison reducing innervation. The squint in this example, is caused by a refractive error in one or both eyes. This refractive error causes poor vision in one eye and so stops the brain from being able to use both eyes together.
Strabismus is often incorrectly referred to as "lazy eye" (which in fact refers to the associated condition amblyopia). It is also referred to as "squint" [8], "crossed eye", "cockeye", "codeye" and "wall eye".[citations needed]
- Duane syndrome
- Mobius syndrome
- Orthoptics
- Pediatric ophthalmology
- Sixth (abducent) nerve palsy
- Strabismus surgery
- Michael Morris, a fictional character with a Lazy Eye
- Vincent Margera, featured in Viva La Bam, has pronounced strabismus.
- ^ http://www.etymonline.com/index.php?term=strabismus
- ^ a b c American Optometric Association. Optometric Clinical Practice Guideline: Care of the patient with strabismus: esotropia and exotropia. 1997.
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8247489&dopt=Abstract
- ^ William Bates. Perfect Sight Without Glasses, Chapter 10.
- ^ Robyn E. Bradley. "ADVOCATES SEE ONLY BENEFITS FROM EYE EXERCISES", The Boston Globe (MA), September 23, 2003.
- ^ http://www.iblindness.org/
- ^ http://www.med.wayne.edu/Scribe/scribe00-01/scribesp01/baker-strabismus.htm
- ^ Squint (NHS health encyclopaedia)
- SEE-KID: Computer-assisted Simulation and Treatment of Eye Motility Disorders
- NHS "Lazy Eye" Site - information about lazy eye (amblyopia) and strabismus (squint)
- VisionSimulations.com | What the world looks like to people with various diseases and conditions of the eye
- Practical approach to diagnosis of strabismus
- Have fun with strabismus - information, demonstration graphics, strabismus surgery