Strabismus

Monte D. Mills, MD

Strabismus - BASICS

Strabismus - description

• From the Greek strabismus (to squint), strabismus is abnormal misalignment of the eyes. The misalignment can be constant or intermittent, and the eyes can be misaligned in any direction.
• When the deviation between the eyes is constant in all gaze positions, the deviation is comitant.
  • Most childhood strabismus is comitant.
• Incomitant strabismus, with a variable angle depending on the direction of gaze, is seen with palsy of cranial nerve III, IV, or VI, and in some strabismus syndromes such as Duane and Brown syndromes and Graves ophthalmopathy.
• Patients with intermittent strabismus may benefit from treatment, even if the deviation is not present constantly.

Strabismus - epidemiology

Most patients with idiopathic comitant strabismus are otherwise developmentally and neurologically normal.

Strabismus - prevalence

Strabismus of all types has an overall prevalence of 4–5%.

Strabismus - risk factors

• Premature birth
• Cerebral palsy
• Seizure disorders
• Developmental delays
• Congenital or acquired loss of vision
• Other ocular abnormalities

Strabismus - genetics

• ~30% of strabismus patients have affected family members.
• Inheritance appears to be multigenic.
• No specific genes have been associated with idiopathic childhood strabismus syndromes
• Genetic causes have been identified for some more rare strabismus syndromes, including congenital fibrosis syndromes (chromosome 12p) and Kearn Sayer syndrome (mitochondrial deletion).

Strabismus - pathophysiology

• No specific pathologic abnormality of the motor nerves, extraocular muscles, or orbits is seen in most patients with idiopathic, comitant strabismus.
• Patients with paretic strabismus demonstrate atrophy of cranial nerves and extraocular muscles.
• Graves disease, myasthenia, and other neuromotor diseases that cause strabismus have specific pathologic features in the extraocular muscles.
• The pathophysiology of the most common forms of childhood strabismus is poorly understood. Infants with strabismus demonstrate subtle abnormalities in both motor function (asymmetric smooth pursuit movements) and binocular sensory function (suppression, anomalous retinal correspondence). No neuroanatomic abnormalities have been consistently demonstrated in infants with idiopathic strabismus.
• Accommodative esotropia, a common strabismus syndrome, is caused by abnormalities in the reflexive convergence and is necessary for looking at near objects.
  • If the ratio of accommodation (focusing for near) to convergence (rotating eyes inward to keep each eye on the target) is abnormally high, focusing on near targets leads to excessive convergence and esotropia.
• Less often, strabismus syndromes are caused by anatomic restriction to extraocular rotation (Graves disease, Brown syndrome), congenital or acquired paresis, or palsy of extraocular muscles (III, IV, or VI palsy, Duane syndrome, Moebius syndrome) or abnormalities of vision (sensory strabismus).

Strabismus - associated conditions

• Strabismus can be a sign of more significant ocular or neurologic abnormality. Retinoblastoma, retinal detachment, brain tumor, and other treatable conditions may initially present with ocular misalignment.
• Frequent coincident ophthalmic diagnoses are amblyopia (30–60%), nystagmus (8–10%), and refractive error (30–50%).

Strabismus - DIAGNOSIS

• Patients rarely “grow out of” strabismus.
• Infants as young as 3 months of age can have careful examinations of eye movement and alignment.
• Delayed diagnosis may worsen prognosis.

Strabismus - signs & symptoms

• The strabismus is identified by the relative direction of the eyes. Esotropia is an inward deviation or crossing; exotropia is an outward deviation; hypertropia and hypotropia are deviations up and down.
• Strabismus is frequently recognized by parents and primary care practitioners, but amblyopia may be asymptomatic.

Strabismus - history

• Age of onset of deviation
• Frequency, duration, and direction of deviation
• Subjective vision problems or complaints
• History of eye or head trauma, premature birth, seizure disorder, neurologic abnormality, or other motor problems
• Previous use of glasses, patching, or other therapy
• Family history of strabismus, amblyopia, refractive error, or childhood vision problems

Strabismus - physical exam

• Patients capable of recognition are tested with charts (letters, pictures, Es), younger patients are tested by the ability to fixate and hold visual fixation on targets (toys, lights) in each eye. It is very important to test each eye separately, in order to detect possible amblyopia and other causes of monocular vision loss (see Amblyopia). Patients capable of reading charts should have complete ophthalmic examination if they cannot recognize at least the 20/40-size target with each eye, or if there is a difference of >1 chart line between eyes.
• Ocular alignment:
  • Hirschberg test: With patient looking at a flashlight, observe the location of the reflection of the light on the corneal surface. Normally, the reflection should be centered in the pupil and symmetric. In strabismus, the reflection will be displaced laterally (esotropia) or medially (exotropia) in 1 eye.
  • Bruchner test: With a direct ophthalmoscope using the largest light, and the patient looking directly at the light, the light is shone into the patient’s eyes. Normally, the pupils should be orange or red and the pupils should symmetrically fill with light. Asymmetric brightness or color between the 2 eyes or shadows in the pupil of either eye is abnormal and may indicate strabismus or other eye problems.
  • Cover test (alternate cover test): With the patient holding his or her visual attention on a single target, the eyes are alternately occluded to force the patient to switch fixation between eyes. Normally, switching fixation should not cause the eyes to move. Movement of the eyes with alternate occlusion signifies strabismus and merits complete evaluation.
• Ocular rotations:
  • Comitant strabismus will demonstrate a consistent angle of deviation in all gaze directions. Incomitant strabismus, including cranial nerve palsies, thyroid ophthalmopathy, and Duane and Brown syndromes, will be greater in 1 direction and smaller or absent in others. Ductions (movements of each eye) may be restricted in certain directions with incomitant strabismus.
• Complete ophthalmic examination, including evaluation of vision, alignment, ocular anatomy, and cycloplegic refraction, is indicated whenever there is suggestion or suspicion of strabismus or abnormal vision based on history, screening tests, or examination.

Strabismus - tests

The diagnosis of strabismus is based on clinical examination, and no laboratory or radiologic tests are routinely necessary.

Strabismus - lab

Serologic testing for antiacetylcholine receptor antibodies is a specific test for myasthenia gravis, a very rare cause of strabismus.

Strabismus - imaging

Depending on the clinical situation, imaging studies of the orbits and brain may be helpful in evaluating cranial nerve palsies, suspected traumatic strabismus, and strabismus associated with neurologic disease.

Strabismus - differencial diagnosis

• The differential diagnosis of abnormal eye movement in childhood includes palsy of cranial nerve III, IV, or VI, orbital fracture or craniofacial anomaly, systemic or localized motor abnormalities such as myasthenia gravis, orbital fibrosis syndrome, infantile botulism, and idiopathic orbital pseudotumor.
• The most common reason for mistaken referral of infants for esotropia is “pseudoesotropia,” caused by wide epicanthal folds giving the false appearance of esotropia.
  • This can be easily recognized by the normal corneal light reflex (Hirschberg test) and normal cover test.
• Sensory strabismus, due to reduced vision in 1 or both eyes, can be comitant or incomitant and can be caused by any ocular, optic nerve, or central cause of vision loss.
  • Sensory deviations are most frequently exotropic, but may be in any direction.
• Special strabismus syndromes include Duane syndrome (congenital aberrant innervation of cranial nerve III), Moebius syndrome (congenital absence of cranial nerve VI and VII), Brown syndrome (congenital or acquired monocular elevation defect due to abnormality of the trochlea-superior oblique tendon complex), myasthenia gravis, and thyroid ophthalmopathy (Graves disease).

Strabismus - TREATMENT

Strabismus - general measures

• Prompt diagnosis and treatment are important for successful outcome from childhood strabismus.
• Depending on the diagnosis, treatment may include glasses, patching, orthoptic exercises, surgery, or a combination of these therapies.
• Glasses are useful, and may be curative, in certain forms of strabismus, especially accommodative esotropia.
  • With accommodative esotropia, glasses reduce or eliminate esotropia by reducing the need to focus the eyes to overcome hyperopia.
• Occlusive therapeutic patching is used to treat amblyopia.
  • In addition to the improved prognosis for long-term stability of surgical correction after amblyopia is treated, patching may sometimes improve alignment even without surgery. However, patching and other amblyopia treatments are usually only an adjunct to strabismus treatment.
• Eye excercises (orthoptic excercises) are useful in certain patients with convergence insufficiency, but are generally not effective in the common forms of childhood esotropia and exotropia.
  • Vision therapy (aside from orthoptic exercises noted above) is not effective for strabismus.

Strabismus - surgery

• Surgery is frequently necessary to realign the eyes to treat strabismus.
  • The ocular insertions of the extraocular muscles are shifted, either weakening or strengthening the muscle’s effectiveness relative to the other muscles.
• In most patients, strabismus surgery can be performed in an ambulatory setting with minimal operative risk and postoperative morbidity.
• In large case series, ~20% of patients require >1 surgery for satisfactory alignment.

Strabismus - FOLLOW UP

Visual acuity testing with each eye separately, and long-term follow-up until patients reach the age of visual maturity (~10 years) is important even after successful treatment.

Strabismus - complications

• Amblyopia occurs in 30–60% of children with strabismus and may require additional treatment.
  • Amblyopia must be recognized and treated early in childhood, during the sensitive period of visual development, to restore normal vision.
• Loss of binocularity (ability to use both eyes together, e.g., depth perception) frequently occurs with strabismus in early childhood.
  • Restoration of normal alignment is necessary for binocularity, and the best binocularity is associated with correction of strabismus in early childhood (before 2 years of age).
  • In older children and adults, diplopia (double vision) may occur.
• The disfigurement of strabismus, with secondary psychologic and social effects, may be a significant problem for children and adults with strabismus.

Strabismus - patient monitoring

• Close monitoring of treatment, and frequent follow-up each 6–12 months after treatment is complete, until visual maturity is achieved at 8–10 years of age is important, due to the frequently unstable outcome of strabismus and amblyopia treatment.
• Most patients will benefit from reassessment each 6–12 months after treatment is complete, until age 10 years.

Strabismus - bibliography

American Academy of Ophthalmology. Preferred Practice Pattern: Esotropia and Exotropia. San Francisco: American Academy of Ophthalmology; 2002.American Academy of Ophthalmology. Preferred Practice Pattern: Pediatric Eye Examination. San Francisco: American Academy of Ophthalmology; 2002Mills MD. Fundamental principles of strabismus surgery. In: Albert DM, ed. Ophthalmic Surgery: Principles and Techniques. Malden, MA: Blackwell Science; 1999.
1. Mills, MD. The eye in childhood. Am Fam Phys. 1999;60:907–918.

Strabismus - CODES

Strabismus - icd9

• 378.00 Convergent (see also Esotropia)
• 378.10 Divergent (see also Exotropia)
• 378.30 Concomitant (see also Heterotropia)
• 378.9 Strabismus (alternating) (congenital) (nonparalytic)

Strabismus - FAQ

• Q: Does strabismus interfere with learning?
• A: No. Patients with normal vision and childhood strabismus should not necessarily have difficulty learning. Learning problems should not be blamed solely on strabismus.
• Q: Is “vision training therapy” an effective treatment for strabismus?
• A: Eye exercises are sometimes helpful in treating a limited number of patients with childhood strabismus. Orthoptic exercises have been effective in only certain specific conditions including convergence insufficiency, and are not effective in the majority of patients with more common types of esotropia and exotropia. There is very little practical or scientific evidence that vision training therapy as commonly practiced has value in patients with comitant childhood strabismus, except for treatment of amblyopia with patching or penalization (see “Amblyopia”).
• Q: Does early surgical correction of strabismus improve the long-term outcome?
• A: Correction of esotropia prior to 2 years of age has been demonstrated to improve the chance of developing normal binocularity. However, not all patients develop binocularity even after early treatment. Many other factors influence the visual outcome in strabismus patients.
• Q: Is correction of strabismus in older children and adults just cosmetic?
• A: No. Older children and adults may have measurable visual improvement after treatment of strabismus, including expansion of visual fields and restoration of binocularity. In addition, the psychologic and social effects of disfiguring strabismus may justify corrective surgery even if no visual improvement is expected.
• Q: In patients with accommodative esotropia treated with glasses, will the glasses be necessary for the rest of the patient’s life?
• A: Many patients wearing glasses for accommodative esotropia are able to stop wearing glasses later in childhood (age 12–14 years) without recurrence of esotropia.

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

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Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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