Case Based Pediatrics For Medical Students and Residents
Department of Pediatrics, University of Hawaii John A. Burns School of Medicine
Chapter XVII.3. Strabismus and Amblyopia
Julie K. Nishimura, MD
July 2002

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A 6 month old female infant presents with crossed eyes. Her parents say her eyes have been crossed since birth, and the left eye seems to cross more than the right. She seems to see fine. She plays with toys and recognizes people across the room. She was a full term infant without perinatal complications, and has no known medical problems.

Exam: She is alert and playful. External: Her left eye is clearly crossed inward (esotropic). There is no facial hemiparesis. Vision: She tracks toys well using both eyes. With the left eye covered, she fixes and follows easily. However, she fusses when the right eye is covered and has more trouble following with this left eye (i.e., she is fussing when the right eye is covered because she can't see as well with her left eye). Motility: Full extraocular movements. There does not seem to be any retraction of the globe on adduction. No nystagmus. Pupils: Equally round and reactive to light; no afferent pupil defect. No leukocoria. Corneal reflection test (Hirschberg test): A penlight is directed toward the cornea, and the reflected image is located temporal to the center of the left pupil. Cover-uncover test: On covering the right eye, there is an outward shift of the left eye. When the eye is uncovered, the left eye shifts back inward. Alternate-cover test: On switching the cover to the left eye, there is an outward shift of the right eye. When the cover is alternated from one eye to the other, there is always an outward shift of the opposite eye.

Clinical course: A referral is made to a pediatric ophthalmologist. No structural ocular abnormalities are found, and there is no significant refractive error. The patient is diagnosed with 1) infantile esotropia and 2) amblyopia, left eye. She wears a patch 6 hours a day over the right eye for a month, and vision in her left eye improves so that she can follow toys equally well with either eye. This also means that either eye crosses spontaneously. She then has surgery to correct her strabismus. Her medial rectus muscles are recessed at age 8 months. Postoperatively, her eyes are straight (orthophoric).


Strabismus (ocular misalignment) is a common pediatric health problem, affecting approximately 5% of U.S. children. If left untreated, strabismus can lead to severe visual consequences, including poor vision and inability to use the eyes together. Strabismic amblyopia is defined as poor vision (usually in one eye, often termed "lazy eye") that results from prolonged ocular misalignment. Amblyopia can be very pronounced (sometimes able to see only hand motions in the affected eye) and is a major cause of blindness among children. Amblyopia can be prevented with timely, appropriate intervention.

There are 2 main forms of strabismus: esotropia and exotropia. Esotropia is an inward deviation of the eyes, and exotropia is an outward deviation. Less common forms include hypertropia (upward deviation) and hypotropia (downward deviation).

Infantile esotropia is the most common type of infantile strabismus. It is defined as an esotropia present by 6 months of age. Previously it was termed congenital esotropia, but many no longer use this term as it is often not noted from birth. There can be a family history of strabismus. Children with infantile esotropia are usually otherwise healthy, although a higher incidence is noted with cerebral palsy and hydrocephalus.

The deviation is usually large, with a definite "crossed-eyes" appearance. The vision can actually be equal in both eyes, but up to 40% will have associated amblyopia. It is actually a good sign if the eyes alternate crossing inward, because this often indicates that vision is approximately equal between the two eyes.

An estimate of the amount of esodeviation can be made with corneal reflection testing. The Hirschberg estimate involves shining a light onto the cornea. If an eye is deviated inward, the light reflex will be temporal to the pupil center.

The definitive method of testing for strabismus is the cover-uncover test. An occluder is placed over the fixing eye. The opposite eye is observed. If there is a deviation of the opposite eye, a tropia is present. If the opposite eye shifts outward, an esotropia is present. If the opposite eye shifts inward, an exotropia is present.

There are a few other entities in the differential diagnosis of infantile esotropia. Pseudoesotropia (pseudostrabismus) is the most common, where a wide, flat nasal bridge with prominent epicanthal folds gives a crossed appearance. Accommodative esotropia is also frequent, where the patient is far-sighted (hyperopic) and the strain to focus causes the eyes to turn inward. This usually occurs in patients older than 6 months of age and is treated with glasses. Sixth-nerve palsy should be ruled out by checking for abduction in both eyes. Sensory deprivation esotropia is caused by unilateral vision-limiting lesions, such as retinoblastoma or cataract. Nystagmus-blockage syndrome features nystagmus dampened by convergence, leading to esotropia. Rarer entities are Duane syndrome (agenesis of the sixth nerve nucleus, accompanied by globe retraction on adduction) and Mobius syndrome (palsy of sixth, seventh, and twelfth cranial nerves).

Treatment of infantile esotropia begins with addressing amblyopia, if present. The stronger eye is patched several hours each day, to develop vision in the weaker eye. Once the vision seems approximately equal, chances for success with surgery are greater. Surgical alignment is usually done with bilateral medial rectus recessions. This procedure involves detaching the medial rectus muscles from their scleral insertion sites, then suturing them to the sclera several millimeters behind the original insertion sites. This effectively weakens the muscles, diminishing their adducting effect. Surgical alignment has traditionally been recommended by two years of age, but more recent studies have supported alignment by one year of age. Earlier surgery provides better levels of stereoscopic depth perception (called stereopsis).

Children need to continue to have close follow-up after surgery, to monitor for postoperative misalignment or amblyopia. They can become overcorrected (exotropia) or have residual esotropia. They sometimes require further surgery for recurrent misalignment and other motility disorders. Alignment to near-orthophoria is the typical goal. This results in a stable alignment with an excellent appearance.


Questions

1. What is the most common form of infantile strabismus?

2. What is the upper age limit in the definition of infantile esotropia?

3. How is amblyopia most commonly treated?

4. Name 3 entities in the differential diagnosis of infantile esotropia.

5. By what age should surgery be undertaken for infantile esotropia?

6. What is the consequence of not recognizing infantile strabismus in a timely fashion?


References

1. Tychsen L. Chapter 8 - Infantile Esotropia: Current Neurophysiologic Concepts. In: Rosenbaum AL, Santiago AP (eds). Clinical Strabismus Management: Principles and Surgical Techniques. 1999, Philadelphia: W.B. Saunders Company, pp. 117-138.

2. Hohberger GG. Chapter 10 - Ocular Motility, Strabismus, and Amblyopia. In: Bartley GB, Liesegang TJ (eds). Essentials of Ophthalmology. 1992, Philadelphia: J.B. Lippincott Company, pp. 246-274.

3. Ing MR, Okino LM. Outcome study of stereopsis in relation to duration of misalignment in congenital esotropia. J Am Assoc Pediatr Ophth Strabis 2002;6(1):3-9.

4. Birch EE, Fawcett S, Stager DR. Why does early alignment improve stereoacuity outcomes in infantile esotropia? J Am Assoc Pediatr Ophth Strabis 2000;4:10-14.

5. Wilson ME, Buckley EG, Kivlin JD, et al. Section 6 - Pediatric Ophthalmology and Strabismus. In: Weingeist TA, Liesegang TJ, Grand MG (eds). Basic Science and Clinical Course. 1999, San Francisco: American Academy of Ophthalmology, pp. 74-116.


Answers to questions

1. Infantile esotropia.

2. 6 months.

3. Patching.

4. Possible answers: pseudoesotropia, accommodative esotropia, sixth nerve palsy, sensory deprivation esotropia, nystagmus-blockage syndrome, Duane syndrome, Mobius syndrome.

5. 1 year of age.

6. The child will have a permanent reduction in visual function. This can range from reduction of stereopsis to total blindness in one eye. It is possible for stereopsis to be lost even if visual acuity is preserved (i.e., measured visual acuity is 20/20) since stereopsis is dependent on vision, plus integration and processing of the images by the brain.


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