strabismus

(strə-bĭz'məs)

[New Latin, from Greek strabismos, condition of squinting, from strabizein, to squint, from strabos, squinting.]

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For more information on strabismus, visit Britannica.com.

noun

The condition of not having the visual axes parallel: cross-eye, squint. See see/not see.

Definition

Strabismus is a condition in which the eyes do not align in the same direction. It is also called crossed eyes or squint.

Description

With normal vision, both eyes focus on the same spot and send the brain the same message. This binocular fixation (both eyes looking directly at the same object) is necessary to see three-dimensionally and to aid in depth perception. When an eye is misaligned, the brain receives two different images. Young children learn to ignore distorted messages from a misaligned eye, but adults with strabismus often develop double vision (diplopia). A baby's eyes should be straight and parallel by three or four months of age. A child who develops strabismus after the age of eight or nine years is said to have adult-onset strabismus.

Esotropia is the most common type of strabismus. It occurs when the eyes turn inward. Infantile esotropia develops in children under the age of six months. Accommodative esotropia develops in children under age three who cross their eyes when focusing on objects nearby. This usually occurs in children who are moderately to highly farsighted (hyperopic). Congenital esotropia is a very rare form of strabismus that occurs with certain birth defects.

Another common form of strabismus is exotropia, sometimes called walleye, where the eyes turn outward. It may only be noticeable when a child looks at distant objects, daydreams, or is tired or sick. Other strabismus conditions include hypertrophia, where the eyes turn upward, and hypotropia, where the eyes turn downward.

With strabismus, in some cases the eye turn occurs always in the same eye; however, sometimes the turn alternates from one eye to the other. Most children with strabismus have comitant strabismus, which means that no matter where they look, the degree of deviation does not change. In incomitant strabismus, the amount of misalignment depends upon which direction the eyes are pointed.

False strabismus (pseudostrabismus) occurs when a child appears to have a turned eye; however, this appearance may actually be due to other factors:

• extra skin that covers the inner corner of the eye
• a broad, flat nose
• eyes set unusually close together or far apart

False strabismus usually disappears as the child's face grows. An eye doctor (ophthalmologist) needs to determine whether the eye turn is true strabismus or pseudostrabismus.

Demographics

Strabismus affects 5 percent of people in the United States or more than 12 million individuals, most of them children. Infantile esotropia affects about 1 percent of full term, healthy babies and a higher percentage of babies born prematurely or born with other facial defects. Congenital esotropia is rare but does not occur at a higher rate in premature babies. Strabismus occurs equally in boys and girls and shows no variation in racial or ethnic distribution. Most strabismus develops in young children, although a few diseases may cause it to develop in adults.

Causes and Symptoms

Strabismus can be caused most often by a defect in the part of the brain that controls eye movement. It is caused less frequently by a defect in the muscles that control eye movement. It is especially common in children who have the following:

• brain tumors
• cerebral palsy
• Down syndrome
• hydrocephalus
• other disorders that affect the brain

Diseases that cause partial or total blindness can cause strabismus. So can extreme farsightedness, cataracts, eye injury, or having much better vision in one eye than the other.

The most obvious symptom of strabismus is an eye that is not always straight. The deviation can vary from day to day or during the day. People who have strabismus often squint in bright sunlight or tilt their heads to focus their eyes.

When to Call the Doctor

Parents should call their doctor whenever they notice their child's eyes appear misaligned, even if the child is very young. A baby whose eyes have not straightened by the age of four months should be examined to rule out serious disease. Strabismus is not a condition that a child will outgrow without medical intervention. Pediatricians can refer parents to an ophthalmologist (eye specialist) skilled in evaluating the vision of very young children.

Diagnosis

Every baby's eyes should be examined by the age of nine months. A pediatrician, family doctor, ophthalmologist, or optometrist licensed to use diagnostic drugs uses drops that dilate the pupils and temporarily paralyze eye-focusing muscles to evaluate visual status and ocular health. Early diagnosis is important. Some eye turns may result from a tumor. Untreated strabismus can damage vision and possibly result in lazy eye (amblyopia).

Treatment

Preserving or restoring vision and improving appearance may involve one or more of the following:

• glasses to aid in focusing and straighten the eye(s)
• patching to force infants and young children to use and straighten the weaker eye
• eye drops or ointments as a substitute for patching or glasses or to make glasses more effective
• surgery to tighten, relax, or reposition eye muscles
• medication injected into an overactive eye muscle to allow the opposite muscle to straighten the eye
• vision training (also called eye exercises)

Prognosis

Early consistent treatment usually improves vision and appearance. The most satisfactory results are achieved if the condition is corrected as early as possible and before the age of seven.

Prevention

Strabismus cannot be prevented, but it can be corrected with early intervention.

Parental Concerns

Parents are often concerned that eye turn is indicative of other vision problems. Sometimes strabismus does accompany other vision defects, so a complete eye examination by a pediatric ophthalmologist is advisable. Delay only increases the difficulty in correcting strabismus, so parents should not wait to see if their child outgrows the condition.

Resources

Books

Plager, David, et al. Strabismus Surgery: Basic and Advanced Strategies. Oxford, UK: Oxford University Press, 2004.

Organizations

American Academy of Ophthalmology. PO Box 7424, 655 Beach Street, San Francisco, CA 94120–7424. Web site: www.aao.org.

American Academy of Optometry. 6110 Executive Boulevard, Suite 506, Rockville, MD 20852. Web site: www.aaopt.org.

American Academy of Pediatric Ophthalmology and Strabismus (AAPOS). PO Box 193832 San Francisco, CA 94119. Web site: www.med-aapos.bu.edu.

Web Sites

Cooper, Jeffrey. "All about Strabismus." Optometrist Network, 2001. Available online at www.strabismus.org (accessed October 31, 2004).

Gerontis, Corina C. "Exotropia, Congenital." Available online at www.emedicine.com/oph/topic330.htm (accessed October 31, 2004).

Ocampo, Vincente V., and C. Stephen Foster. "Exotropia, Infantile." Available online at www.emedicine.com/oph/topic328.htm (accessed October 31, 2004).

Stidham, D. Brian, and Chris Noyes. "Exotropia, Accommodative." Available online at www.emedicine.com/oph/topic330.htm (accessed October 31, 2004).

[Article by: Tish Davidson, A.M. Maureen Haggerty]

Tutor's tip: This word was used in the 2006 Scripps National Spelling Bee finals.

LearnThatWord.com is a free vocabulary and spelling program where you only pay for results!

Deviation of the eye that the patient cannot overcome; the visual axes assume a position relative to each other different from that required by the physiological conditions. Called also squint.

Basic types of strabismus. By permission from Guyton R, Hall JE, Textbook of Medical Physiology, Saunders, 2000

• comitant s. — extraocular muscles are not paralyzed and the degree of deviation is the same in all directions.
• congenital s. — medial strabismus is seen in Siamese cats. See convergent strabismus (below).
• convergent s. — that in which the visual axes converge; esotropia, or cross-eye. A frequent finding in Siamese cats, related to an anomaly of neuronal pathways between the retina and lateral geniculate nucleus in which more neurons project contralaterally rather than ipsilaterally as in other cats.
• divergent s. — that in which the visual axes diverge; called also exotropia and walleye.
• inherited s. — see inherited exophthalmos.
• noncomitant s. — deviation due to paralysis of one or more muscles.
• traumatic s. — a complication of traumatic prolapse of the eye, due to rupture of extraocular muscles.

An abnormal ocular condition in which the eyes are crossed.

• Sickly, out of shape, dull, or weak

For the protein Strabismus, see Strabismus (protein).

Strabismus
Classification and external resources
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 (English pronunciation: /strəˈbɪzməs/; Modern Latin, from Greek στραβισμός strabismos; cf. στραβίζειν strabizein "to squint", στραβός strabos "squinting, squint-eyed"^[1]), also known as heterotropia,^[2] is a condition in which the eyes are not properly aligned with each other.^[3] 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 and preventing proper binocular vision, which may adversely affect depth perception.

Strabismus can be either a disorder of the brain in coordinating the eyes, or of one or more of the relevant muscles' power or direction of motion. Difficult strabismus problems are usually co-managed between orthoptists and ophthalmologists.

Contents 1 Classification 1.1 Paralytic strabismus 1.2 Other strabismus 2 Signs and symptoms 3 Pathophysiology 4 Diagnosis 4.1 Laterality 4.2 Onset 4.3 Differential diagnosis 5 Management 6 Prognosis 7 See also 8 References 9 External links

Classification

Paralytic strabismus

Forms of paralytic strabismus include

• Third (oculomotor) nerve palsy
• Fourth (trochlear) nerve palsy
  • Congenital fourth nerve palsy
• Sixth (abducent) nerve palsy
• Total (external) ophthalmoplegia
• Progressive external ophthalmoplegia
• Other
  • Kearns-Sayre syndrome

Other strabismus

Other forms of strabismus include:

• Convergent concomitant/Divergent concomitant
  • Esotropia
  • Exotropia
• Vertical strabismus
  • Hypertropia
  • Hypotropia
• Other and unspecified heterotropia
  • Microtropia
  • Monofixation syndrome
• Heterophoria
  • Esophoria
  • Exophoria
• Mechanical strabismus
  • Brown's sheath syndrome
• Other
  • Duane syndrome

Signs and symptoms

One eye moves normally, while the other points in (esotropia or "crossed eyes"), out (exotropia), up (hypertropia) or down (hypotropia).

Strabismus is often mistakenly referred to as "lazy eye" or known as amblyopia; a result from constant unilateral strabismus. It is also referred to as "crossed eyes", “wandering eyes”, or having a “cast”.^[4] Other names include "squint",^[5] "crossed eye", "google eye", "boss eye", "cock eye", "wonk eye", "codeye", "derpy eye", and "wok eye".^{[citation needed]}

"Cross-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle less than zero; the optic axes overconverge. "Wall-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle greater than zero; that is, the optic axes diverge from parallel.

Pathophysiology

Strabismus can be caused when the cranial nerves III (oculomotor), IV (trochlear) or VI (abducens) have a lesion. 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 VI is particularly vulnerable to damage from brain swelling, as it runs between the clivus and brain stem.

More commonly however, squints are termed concominant (i.e. non paralytic). This means the squint is not caused by a lesion 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.

Diagnosis

During eye examinations, orthoptists, 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 "straight" eye is covered, as long as the vision in this eye is good enough. If the "straight" 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); these are types of horizontal strabismus. "Hypertropia" is upward, and "Hypotropia" is downward; these are types of vertical strabismus, which are less common.

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, then the reflection will be in the same spot of each eye. Therefore, if the reflection is not in the same place in each eye, then the eyes aren't properly aligned.

Laterality

Strabismus may be classified as unilateral if the same eye consistently 'wanders', or alternating if either of the eyes can be seen to 'wander'. Alternation of the strabismus may occur spontaneously, with or without subjective awareness of the alternation. Alternation may also be seen following the cover test, with the previously 'wandering' eye remaining straight while the previously straight eye is now seen to be 'wandering' on removal of the cover. The cover-uncover test is used to diagnose the type of strabismus (also known as tropia) present.^[3]

Onset

Strabismus may also be classified based on time of onset, either congenital, acquired or secondary to another pathological process, such as cataract.^[3] Many infants are born with their eyes slightly misaligned. The best time for physicians to assess this is between ages 3 and 6 months.^[6]

Differential diagnosis

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.

Management

Surgery to correct strabismus on an eight-month-old Nicaraguan infant.

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.^[7]

Whereas amblyopia (lazy eye), 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 does not change the vision; it 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. The procedure can typically be performed in about an hour, and requires about a week for recovery. Double vision can result, and occasionally vision loss can occur. 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. Most children eventually recover from amblyopia by around age 10, if they have had the benefit of patches and corrective glasses.^[6]

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.

Botulinum Toxin (Botox) may also be used in the treatment of strabismus, to improve cosmetic appearance. Most commonly used in adults, the toxin is injected in the stronger muscle, causing temporary paralysis. The treatment may need to be repeated 3–4 months later once the paralysis wears off. Common side effects are double vision, droopy eyelid, over correction and no effect. The side effects will resolve fairly quickly.

In adults with previously normal alignment, the onset of strabismus usually results in double vision (diplopia).

Prognosis

When strabismus is congenital or develops in infancy, it can cause amblyopia, in which the brain ignores input from the deviated 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."^[8]

See also

• Orthoptist
• Duane syndrome
• Möbius syndrome
• Orthoptics
• International Orthoptic Association
• Pediatric ophthalmology
• Retinoblastoma
• Palsy of cranial nerve III (oculomotor), IV (trochlear), VI (abducens)
• Strabismus surgery
• Amblyopia
• Bates method

References

1. ^ Online Etymology Dictionary
2. ^ http://dictionary.reference.com/browse/strabismus
3. ^ ^{a b c} American Optometric Association. Optometric Clinical Practice Guideline: Care of the patient with strabismus: esotropia and exotropia. 1997.
4. ^ http://www.orbis.org/Default.aspx?cid=5615&lang=1
5. ^ Squint (NHS health encyclopaedia)
6. ^ ^{a b} Nield, LS; Mangano, LM (April 2009). "Strabismus: What to Tell Parents and When to Consider Surgery". Consultant 49 (4). http://www.consultantlive.com/display/article/10162/1399809. 
7. ^ Eskridge JB (October 1993). "Persistent diplopia associated with strabismus surgery". Optom Vis Sci 70 (10): 849–53. doi:10.1097/00006324-199310000-00013. PMID 8247489. 
8. ^ Scribe/Alum Notes Winter 2001 – Template

External links

Wikimedia Commons has media related to: Strabismus

• NHS "Lazy Eye" Site – information about lazy eye (amblyopia) and strabismus (squint)
• Practical approach to diagnosis of strabismus
• Have fun with strabismus – information, demonstration graphics, strabismus surgery

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