Based on these findings, this infant is diagnosed with infantile esotropia and amblyopia of the left eye.
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 either by reduced or no transmission of visual stimulus into the eye and through the optic nerve and to the brain for a prolonged duration during infancy and early childhood. For the visual system to develop properly, human 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.
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. Further treatment can include refractive correction with glasses for anisometropia and surgical realignment of the eyes if strabismus is the ultimate cause.
There are many potential causes of amblyopia, including anisometropia (differential in refraction 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.
There is also a wide differential diagnosis for strabismus. One of the most common is pseudostrabismus, where prominent epicanthal folds give the appearance of crossed eyes. Accommodative esotropia occurs with a high accommodative convergence to accommodation ratio, resulting in crossed eyes with near focusing. Many different syndromes are associated with palsies of the nerves that innervate the extraocular muscles and can be elucidated with extraocular motility and head tilt testing. In adults, entrapment of extraocular muscles due to trauma or enlargement of the extraocular muscles due to graves orbitopathy can lead to strabismus.