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- Strabismus is defined as any form of ocular misalignment. It derives from the Greek word strabismos (to squint).
- Strabismus can be intermittent or constant.
- There are many types of strabismus, which are defined by the direction of misalignment.
- Exotropia: out-turning of eyes
- Esotropia: in-turning of eyes
- Hypertropia: one eye higher than the other eye
- Strabismus can be comitant (amount of misalignment is the same in all directions of gaze) or incomitant (variable angle of deviation, which is dependent on the direction of gaze).
- Comitant strabismus is the most common form of strabismus. These children are typically developmentally normal.
- Incomitant strabismus is less common. It is caused by paralytic strabismus such as cranial nerve palsies or restrictive strabismus such as Brown syndrome.
- Strabismus may cause permanent loss of three-dimensional vision, amblyopia (visual acuity loss), and/or ocular torticollis.
- Strabismus can result in significant psychosocial problems for children, which warrant attention.
- Patients with intermittent strabismus can also develop lifelong loss of depth perception and visual acuity. These children should be evaluated and potentially treated for their strabismus.
For children younger than 6 years of age, the prevalence of strabismus is 4–5%.
- Low birth weight
- Maternal cigarette smoking
- Retinopathy of prematurity
- Refractive errors: high hyperopia and anisometropia
- Congenital or acquired vision loss
- Cerebral palsy
- Craniofacial syndromes
- Seizure disorders
- Developmental delays
- There is a 4-fold increase in the risk of strabismus for a child with an affected family member.
- There is limited knowledge of the genetic inheritance patterns of common strabismus. There appears to be polygenic pattern, but the STBMS1 gene has been isolated as a specific locus for a few individuals.
- There is a limited understanding of the pathophysiology of the most common comitant strabismus. There is no specific pathologic abnormality of the cranial nerves, extraocular muscles, or orbits. Therefore, a “tight” or “weak” muscle is not the cause of the strabismus problem.
- Accommodative esotropia is a common form of strabismus in young children. It is associated with high hyperopia (farsightedness) and anisometropia (see “Refractive Error”). When a child with high hyperopia attempts to focus at any distance, he or she needs to focus his or her intraocular lens (accommodation). This focusing can trigger overconvergence of the eyes (esotropia).
- Paretic strabismus is caused by weakness of cranial nerves and their associated extraocular muscles. Examples of this type of pathology include cranial nerve palsies—III, IV, and VI; Möbius syndrome; or Duane syndrome.
- Neuromuscular diseases such as myasthenia gravis can cause strabismus with decreased extraocular muscle function.
- Restrictive strabismus is a result of muscle tightness causing a limitation in eye movement. Examples include Graves disease, Brown syndrome, or trauma to extraocular muscles.
- Sensory strabismus results from poor visual acuity in one eye.
Commonly Associated Conditions
- Strabismus can be a sign of a vision- or life-threatening neurologic problem.
- A physician needs to consider that retinoblastoma, brain tumor, cataract, and other conditions may initially present with ocular misalignment.
- Other ocular problems often coexist with strabismus including amblyopia, nystagmus, and refractive error.