Basics
Description
- 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.
Epidemiology
Prevalence
For children younger than 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
Genetics
- 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.
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. 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; M ¶bius 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.
Diagnosis
- It is normal for infants younger than 2 months of age to have intermittent strabismus but not constant strabismus.
- After 4 months of age, any strabismus is abnormal and warrants an ophthalmologic exam.
- Children do not commonly "grow out " of strabismus.
- A delay in diagnosis and treatment can lead to a worse prognosis for normal visual development.
Signs and Symptoms
- Children are typically asymptomatic. Because the brain suppresses one eye in childhood strabismus, the patient has no diplopia and is not aware of ocular misalignment.
- Strabismus needs to be screened for and identified by primary care providers and family members.
History
- Onset of misalignment
- Frequency, duration, and direction of deviation
- Torticollis
- History of eye or head trauma
- Birth and developmental history focusing on prematurity, seizure disorder, or neurologic abnormality
- History of glasses, patching, or other vision therapy
- Family history of strabismus, amblyopia, refractive error, or childhood vision problems
Physical Exam
- Patient 's visual acuity should be evaluated in an age-appropriate manner individually for each eye (see "Amblyopia " and "Refractive Error " ).
- The presence of torticollis may indicate strabismus.
- Ocular alignment
- Corneal light reflex (Hirschberg test): With a patient looking at a light, look for the location of the corneal light reflex. The light reflex should be focused at the center of each pupil symmetrically. If the reflex is located outside of the pupillary center and asymmetric, the child likely has strabismus. If it is positioned laterally, the child has esotropia, and if it is positioned medially, the child has exotropia.
- Red reflex test (Br ¼ckner): With dimmed room lights, an examiner uses a direct ophthalmoscope to look at the red reflex of both eyes simultaneously from 2 " 3 feet. Normally, the pupils should be red and the pupils should symmetrically fill with light. If there is asymmetry to the brightness, a dulled reflex, or a black or white area within the reflex, there is likely an ocular problem, which could be strabismus.
- Alternate cover test: The examiner should get the patient to focus on a single target. While they are holding fixation, the examiner should occlude each eye for a brief period of time. The examiner should watch for movement of the eye to pick up fixation. If the eyes remain still while you alternately occlude each eye, then there is no strabismus. If the eyes move from inward to outward, the child has esotropia. If the eyes move from outward to inward, the child has exotropia.
- Ocular rotations
- Each eye should be evaluated for full movement in horizontal and vertical directions. If the eye has limited movement in a particular direction, then there may be paralytic or restrictive strabismus. If there is limited movement, a patient should be evaluated by an ophthalmologist urgently.
- Complete ophthalmic examination is indicated whenever there is suspicion of strabismus or abnormal vision based on history, screening tests, or examination.
Diagnostic Tests & Interpretation
Serologic or radiologic testing is rarely performed to work up the etiology of routine strabismus.
Lab
- In select patients, a physician may order antiacetylcholine receptor antibodies testing to test for myasthenia gravis or thyroid function studies to test for thyroid eye disease.
Imaging
If orbital or neurologic pathology is suspected, an MRI or CT scan may be performed to evaluate for a restrictive or paralytic strabismus.
Differential Diagnosis
- In the initial evaluation, one needs to differentiate between true strabismus and pseudostrabismus.
- Children with wide epicanthal folds often give the false appearance of esotropia due to minimal amount of conjunctiva showing in the medial canthal region.
- Rather than looking at the amount of "whites " showing, a practitioner can use the corneal light reflex (Hirschberg test) to see if the light reflex lies in the central pupil and perform a cover test.
- If there is any doubt about the presence of strabismus, a referral to an ophthalmologist is warranted.
- In children with abnormal eye movements (incomitant strabismus), the differential diagnosis includes the following:
- Cranial nerve palsies (III, IV, or VI)
- Craniofacial anomalies
- Orbital fracture
- Systemic or localized motor abnormalities such as myasthenia gravis
- Orbital pseudotumor
- Thyroid eye disease (Graves)
- Strabismus syndromes
- Strabismus syndromes include the following:
- Duane syndrome: congenital aberrant innervation of cranial nerve III
- M ¶bius syndrome: congenital absence of cranial nerve VI and VII
- Brown syndrome: an abnormality of the trochlear-superior oblique tendon causing a monocular elevation deficit
- Sensory strabismus is caused by any form of vision loss. The strabismus can be either esotropia or exotropia. If a child has sensory strabismus, it is crucial to identify the cause of vision loss because it can be life threatening (such as retinoblastoma or intracranial tumor).
Additional Treatment
General Measures
- If a child remains strabismic for a prolonged period, it can result in irreversible loss of depth perception and vision loss (amblyopia). Therefore, it is imperative that a child receives prompt evaluation and treatment.
- Treatment options can include glasses, occlusion therapy, orthoptic exercises, surgery, or a combination of these therapies.
- Glasses are primary treatment for a common form of strabismus " accommodative esotropia.
- Occlusion therapy is typically used for amblyopia rather than strabismus. If occlusion therapy improves vision, occasionally, the strabismus may improve, but more importantly, better vision improves prognosis for strabismus treatment.
- Eye exercises (orthoptic exercises) are useful in patients with convergence insufficiency. There is no evidence that they improve typical childhood esotropia and exotropia.
Surgery/Other Procedures
- If patching and glasses do not improve strabismus, then surgery is often recommended to improve binocular vision.
- In strabismus surgery, the eye muscles are either weakened by moving the muscle 's insertion or tightened (strengthened) by removing a small piece of muscle tissue.
- For most patients, strabismus surgery is performed in an outpatient setting with minimal risk or morbidity.
- In large-case series, there is ¢ ¼80% success rate for surgery and a ¢ ¼20% reoperation risk.
Ongoing Care
Long-term follow-up is important for children to monitor their vision development until at least 10 years of age. There is a risk for amblyopia and strabismus recurrence even after a successful surgical correction.
Additional Reading
- American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Preferred Practice Pattern ®; Guidelines. Esotropia and Exotropia. San Francisco: American Academy of Ophthalmology; 2012. http://www.aao.org/ppp. Accessed March 17, 2015.
- American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Preferred Practice Pattern ®; Guidelines: Pediatric Eye Evaluations. San Francisco: American Academy of Ophthalmology; 2012. http://www.aao.org/ppp. Accessed March 17, 2015.
- Handler S, Fierson WM, Section on Ophthalmology, et al. Learning disabilities, dyslexia, and vision. Pediatrics. 2011;127(3):e818 " e856. [View Abstract]
Codes
ICD09
- 378.9 Unspecified disorder of eye movements
- 378.10 Exotropia, unspecified
- 378.00 Esotropia, unspecified
- 378.30 Heterotropia, unspecified
- 378.31 Hypertropia
- 378.20 Intermittent heterotropia, unspecified
- 378.50 Paralytic strabismus, unspecified
ICD10
- H50.9 Unspecified strabismus
- H50.10 Unspecified exotropia
- H50.00 Unspecified esotropia
- H50.40 Unspecified heterotropia
- H50.30 Unspecified intermittent heterotropia
- H50.22 Vertical strabismus, left eye
- H50.21 Vertical strabismus, right eye
- H49.9 Unspecified paralytic strabismus
SNOMED
- 22066006 Strabismus (disorder)
- 399054005 Exotropia
- 16596007 Esotropia (disorder)
- 128602000 heterotropia (disorder)
- 400942002 paralytic strabismus (disorder)
- 40608009 Hypertropia
- 27590007 Intermittent esotropia
- 2967003 Non-comitant strabismus (disorder)
FAQ
- Q: Will a child 's strabismus resolve on its own?
- A: In most cases, children do not outgrow strabismus. Diagnosis and treatment should not be delayed.
- Q: Should a child wait to have surgery until he or she is older?
- A: When a child has strabismus, there are anatomic changes to the brain to prevent diplopia. The longer a child spends strabismic, the more adaptation occurs and the harder it is to regain normal depth perception. Therefore, it is important not to delay diagnosis and treatment. There is improved prognosis with prompt treatment.
- Q: Does strabismus cause learning difficulties?
- A: There is no proven association between strabismus and learning disabilities. If a child has learning difficulties and has strabismus, the learning issues should be evaluated outside of the strabismus.
- Q: How does loss of depth perception affect a child?
- A: A child may demonstrate subtle changes in fine motor skills, visual " spatial tasks, and athletic capabilities.
- Q: Will surgery in older children and adults improve their ocular function?
- A: With surgery, older children and adults may expand their visual fields and restore binocularity. The psychosocial effects of strabismus can significantly affect a person 's sense of self and social interaction. For this reason, strabismus surgery can dramatically improve quality of life.
- Q: When is vision therapy prescribed for strabismus?
- A: Vision therapy has limited use for patients with strabismus. Eye exercises have been proven effective for one type of exotropia called convergence insufficiency. For most childhood strabismus, there is no evidence that vision therapy successfully treats ocular misalignment.