Diagnosis: Accommodative Esotropia
This is a case of strabismus, specifically acccommodative esotropia.
Strabismus, or ocular misalignment of the eye, is a common pediatric condition. It arises when the eye muscles do not work together to produce a single image. When eye deviation occurs, the brain will try to compensate by ignoring the visual input from the deviated eye. This can lead to amblyopia, which refers to poor development of visual acuity from causes such as ocular misalignment, significant refractive error, or structural abnormalities. With strabismic amblyopia, the eye can be structurally normal but will not achieve 20/20 vision because brain is suppressing the image received from the eye due to ocular misalignment.
Why is amblyopia important? Amblyopia can be reversible if the underlying cause is corrected while the patient is young (<13 years of age). Once the patient reaches visual maturity (>13 years old), the visual pathways are less adaptable and the brain suppression of the eye may become permanent. If a patient with accommodative esotropia has amblyopia of one eye from misalignment, prompt correction of the misalignment can help to reverse the amblyopia. Once the eyes are realigned, the brain no will longer suppress the eye and vision can continue to develop. However if the esotropia is addressed at an older age, correcting the strabismus may not improve the amblyopia because the visual pathway has matured, resulting in permanent decreased vision.
Strabismus can be classified by the direction of the deviation: hypertropia, hypotropia, exotropia, or esotropia, and can be further classified by the cause and onset. In this case, the patient has accommodative esotropia of the right eye. Accommodative esotropia is an acquired form of esotropia that typically presents between the ages of 2-4 years. It will often begin intermittently and then quickly become constant. The pathophysiology is related to an imbalance between the medial recti (converging) muscles and ciliary body (accommodation). The patient will have difficulties with near vision (hyperopia) and will try to increase accommodation (focusing power) in order to see the close-up object more clearly. In certain patients, this can lead to excessive convergence and subsequent eye crossing. It is important to remember that it is normal for pediatric patients to have some degree of hyperopia. However, patients with severe hyperopia (greater than +2.00D) can develop this particular form of strabismus. (Upper left image credit: CC BY-SA 4.0).
The other most common types of strabismus include congenital esotropia and intermittent exotropia. Congenital esotropia occurs at birth or within six months of age and patients will typically have a very large angle of deviation (>30 PD). The deviation is constant. Intermittent exotropia tends to arise between the ages of 10 months and 4 years. Because the eye deviation happens infrequently, it can be difficult to detect. The exotropia will typically only arise when seeing objects far away. A classic sign is closing, or “squinting” of the bad eye when looking into the sun.
Of note, strabismus should be distinguished from pseudostrabismus. In pseudostrabismus, the eyes may appear falsely misaligned due to large epicanthal folds or a wide nasal bridge. In pseudostrabismus the corneal light reflex, cover, and alternating cover tests are normal. Furthermore, normal newborns can have physiologic intermittent strabismus. This can be present as early as birth but will typically resolve by 2 months. Any child with intermittent crossing after two months of age, or persistent crossing at any age should be referred immediately to a pediatric ophthalmologist.
General risk factors for strabismus include family history, preterm birth or premature weight, history of ocular conditions that obstruct the visual axis (i.e ptosis, cataracts, retinoblastoma), developmental abnormalities (Down’s syndrome, hydrocephalus) and neuromuscular conditions (Graves’ disease or cerebral palsy).
Strabismus is a clinical diagnosis and thus a thorough history and physical exam are warranted. The physical exam should include tests such as the corneal light reflex test, cover-uncover test, alternate-cover test, and cycloplegic refraction. Cycloplegic refraction allows for the full refractive error to be measured without be confounded by accommodation. Further work-up should be conducted if there is concern that the strabismus is secondarily caused (e.g. retinoblastoma).
Treatment for strabismus includes correction of the underlying cause of the misalignment in order to restore binocular vision. Strategies include prescription glasses to correct refractive error, occlusion therapy (covering the normal eye), pharmacologic therapy (i.e. atropine to impair sight of the normal eye), and surgery to realign the eyes. Surgical techniques for horizontal ocular deviations commonly include recessions or resections of the eye muscles to achieve ocular alignment.
References and Additional Resources:
1. Boyd K.“Strabismus in Children.” Lipsky SN, Turbert D. (Eds). Eye Health A-Z. December 2020 .Available at: https://www.aao.org/eye-health/diseases/strabismus-in-children.
2. Leuder G. “Chapter 9. Strabismus in Infants.” Pediatric Ophthalmology. St. Louis, McGraw-Hill Medical, 2011.
3. Mestre C, Otera C, Diaz-Douton F et al. “An automated and objective cover test to measure heterophoria.” PloS One. 2018;13(11)e0206674.
4. Coats D, Payasse EA, Olitsky SE, Armsby C. “Evaluation and management of strabismus in children.” Olitsky SE, Armsby C. (Eds). UptoDate. Available at: https://www-uptodate-com.eresources.mssm.edu/contents/evaluation-and-management-of-strabismus-in-children?search=stabismus&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H3.
5. Ferris J. “Amblyopia: Atropine” Clinical Education: Basic Skills Video. October 2015. Available at: https://www.aao.org/basic-skills/amblyopia-atropine.
6. Helveston EM. “Understanding, detecting, and managing strabismus.” Community Eye Health. 2010;23(72):12-14.
7. “Accommodative Esotropia.” American Association for Pediatric Ophthalmology and Strabismus: Eye Terms and Conditions. March 2019. Available at: https://aapos.org/glossary/accommodative-esotropia.
8. Heidar K, Miller AM, Kozak A, et al. “Accommodative Esotropia” Grigorian AP (Eds). American Academy of Ophthalmology: EyeWiki. February 2021. Available at: https://eyewiki.aao.org/Accommodative_Esotropia.
9. Clarke WN. Common types of strabismus. Paediatr Child Health. 1999;4(8):533-535.
Case 2 Index