Strabismus

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Strabismus is defined as any form of ocular misalignment.
  • Strabismus can be intermittent or constant.
  • There are many types of strabismus, which are defined by the direction of misalignment.
    • Esotropia: inward or nasal deviation of the eyes
    • Exotropia: outward or temporal deviation of the eyes
    • Hypertropia: one eye elevated above the other eye
  • Strabismus can be comitant (amount of misalignment is the same in all directions of gaze) or incomitant (variable angle of deviation, 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 depth perception, amblyopia (decreased vision), and/or ocular torticollis.
  • Strabismus can result in significant psychosocial problems for children, which warrant attention and treatment.
  • 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.

EPIDEMIOLOGY

Prevalence

For children <6 years of age, the prevalence of strabismus is 4–5%.

RISK FACTORS

  • 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
  • Hydrocephalus
  • Neurologic problems—stroke, brain tumor
  • Family history of strabismus

Genetics

  • There is a 4-fold increase in the risk of strabismus for a child with an affected 1st-degree relative.
  • 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.

PATHOPHYSIOLOGY

  • 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.
  • Accommodative esotropia is a common form of strabismus in young children. It is associated with high hyperopia (farsightedness) and anisometropia (see “Refractive Error” chapter). When a child with high hyperopia attempts to focus at any distance, they need to focus their intraocular lens (accommodation). This focusing can trigger overconvergence of the eyes, resulting in 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. Strabismus in these cases tends to be incomitant.
  • 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.

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