Patient History
HPI:
A 6 month-old female infant presents with occasional crossing of her eyes. Her parents believe that her left eye deviates nasally more than the right. The infant responds to light, tracks faces, and plays with toys without issue.

Past Ocular History:
None

Ocular Medications:
None

Past Medical History:
Born at term without complications.

Surgical History:
None

Past Family Ocular History:
Mother with refractive error and maternal uncle with “lazy eye”. Paternal history unremarkable.

Social History:
Lives at home with mom and dad. No smokers in home.

Medications:
None

Allergies:
None

ROS:
Otherwise negative

Ocular Exam
Visual Acuity (cc):
OD: Fixes and follows
OS: Fixes and follows

IOP (tonoapplantation):
OD: soft by palpation
OS: soft by palpation

Pupils:
Equal, round and reactive to light, no APD. No leukocoria.

Extraocular Movements:
Full OU. No nystagmus.

Confrontational Visual Fields:
Responds to light directed in four quadrants with each eye

External:
Her left eye is crossed inward (esotropic). Her face is symmetric.

Slit Lamp:

Lids and Lashes	Normal OU
Conjunctiva/Sclera	Normal OU
Cornea	Clear OU
Anterior Chamber	Grossly normal
Iris	Normal OU
Lens	Clear OU
Anterior Vitreous	Clear OU

Dilated Fundus Examination:

OD	Clear view, CDR 0.2 with sharp optic disc margins, no optic nerve hypoplasia, flat macula with normal foveal light reflexes, normal vessels
OS	Clear view, CDR 0.2 with sharp optic disc margins, no optic nerve hypoplasia, flat macula with normal foveal light reflexes, normal vessels

Other:
Corneal reflection test (Hirschberg test): Reflection of a penlight directed at the infant is located in the center of the R pupil and at the temporal margin of the left pupil.

Cover-uncover test: On covering the R eye, the left eye shifts outward and fixes intermittently to a toy straight ahead. When the right eye is uncovered, the left eye shifts back inward. When covering the L eye the right eye remains straight looking at the target.

Alternate-cover test: When the cover is alternated from one eye to the other, there is an outward shift of the opposite eye on uncovering. Deviation measured at approximately 25 prism diopters base out.

Stereopsis: Unable to determine given patient age.

Retinoscopy: mild hyperopia OU (+1.00) without astigmatism

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. 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 seen until age 9 or 10 when the visual system is still maturing. Treatment consists of patching or atropine penalization of the non-amblyopic eye, so that the amblyopic eye is forces to attend to visual stimuli and allow for developmental recovery. If the amblyopia is due to strabismus, surgery will likely be indicated.

1. Which is not a cause of amblyopia?
   • anisometropia (difference in refraction between the two eyes)
   • congenital ptosis
   • optic nerve hypoplasia
   • pseudostrabismus
2. What is NOT an appropriate treatment for amblyopia?
   • Patching the stronger eye
   • Doing strabismus surgery to align the eyes.
   • Waiting until the patient is in their teenage years to see if the weaker eye will become stronger with time
   • Placing dilating eye drops in the stronger eye to blur this eye
   • Using glasses to correct any refractive error
3. What is the correct term to describe eyes that are misaligned so one eye is inward?
   • Exotropia
   • Esotropia
   • Pseudotropia
   • Hypotropia

    

   References/Resources:
   Basic and Clinical Sciences Course Section 6: Pediatric Ophthalmology and Strabismus. Section chair: Gregg T Lueder, MD

Which is not a cause of amblyopia?

d. Pseudostrabismus

All the other diagnoses can result in amblyopia for the affected eye.



What is NOT an appropriate treatment for amblyopia?

c. Waiting until the patient is in their teenage years to see if the weaker eye will become stronger with time

Treatment of amblyopia should be started as soon as diagnosed and as young as possible.



What is the correct term to describe eyes that are misaligned so one eye is inward?

b. Esotropia