Diagnosis
Infantile esotropia and amblyopia of the left eye
Discussion
Differential Diagnosis:
This patient is presenting with infantile esotropia. Other diagnoses to consider are pseudostrabismus (where prominent epicanthal folds give the appearance of crossed eyes) and accommodative esotropia (the convergence movement of the eyes is stronger than needed for accommodation - this results in esotropia with near focusing). Palsies of the nerves that innervate the extraocular muscles (ex. cranial nerve 6) could result in esotropia. In adults, entrapment of extraocular muscles due to trauma or enlargement of the extraocular muscles due to graves orbitopathy can lead to strabismus. Systemic conditions, such as brain tumor or meningitis can cause sudden eye deviations. In this patient the eye exam revealed no extraocular muscle restriction or deficit and no refractive error. Her overall health was also normal.
Definition:
Strabismus refers to the misalignment of the eyes and can present in a variety of ways. The most common forms are esotropia (inward deviation) and exotropia (outward deviation). Strabismus can also present as hypertropia (upward deviation) or hypotropia (downward deviation). Nasally directed misalignment of the eyes, or esotropia, that presents at < 6 months of age without other ocular findings is classified as infantile esotropia. The cause of infantile esotropia is unknown, but it is associated with maldevelopment of stereopsis, motion processing, and eye movements. Although vision can be normal in both eyes, up to 40% of these patients will have amblyopia. Amblyopia is defined as poor vision, either unilaterally or bilaterally, in an eye that is otherwise normal on clinical exam. Amblyopia is caused by reduced transmission of visual stimulus from the eye through the optic nerve to the brain for a prolonged duration during infancy and early childhood. For the visual system to develop properly, infants need to have adequate and symmetric exposure to visual stimuli. In the case of our patient, she has strabismic amblyopia of the left eye due to ocular misalignment.
Examination:
There are many potential causes of amblyopia, including anisometropia (unequal refractive error between eyes), strabismus (misaligned eyes), visual deprivation (secondary to cataract, ptosis, etc.), and organic (optic nerve hypoplasia, retinoblastoma). A complete ophthalmic exam including retinoscopy to determine refractive error and rule out cataracts, cover/uncover testing to unmask strabismus, and a dilated fundus exam to rule out optic nerve or retinal pathology should be done as part of the work-up for amblyopia.
Treatment:
If recognized early and treated aggressively, amblyopia can be reversible to an extent. Treatment is most effective at early ages but results can be see until age 9 or 10 when the visual system is still maturing. Treatment consists of compromising the vision in the strong eye with either eye patches or drops to blur the eye so that the amblyopic eye is forced to attend to visual stimuli and allow for developmental recovery. If the amblyopia is due or worsen by strabismus the patient needs surgical realignment of the eyes. Refractive correction with glasses is important for anisometropia (unequal refractive error between the eyes).
