A 15-month-old boy presents with his mother for his well-child exam. His mother is concerned about his vision, as she noticed him squinting while watching television. The patient was born at 39 weeks of gestation via spontaneous vaginal delivery. He is up to date with routine vaccinations. He is able to walk alone, speak 3 words, and scribble with a crayon. His temperature is 98.6°F (37.0°C), blood pressure is 80/55 mmHg, pulse is 105/min, and respirations are 25/min. On exam, his pupils are round and reactive to light. A photograph of his eyes is shown in Figure A. When focusing on the pediatrician's penlight, the patient's left eye wanders. However, when the right eye is covered, the left eye refocuses on the light. The rest of his neurological exam, including extraocular movements, is within normal limits. Which of the following is the most appropriate next step in management for this patient?
Perform a Bielschowsky head tilt test
Brain MRI
Patch the left eye
Patch the right eye
Patch the right eye
This patient, with a history that suggests decreased visual acuity, a positive cover test (refixation of the misaligned eye upon covering the appropriately aligned eye), and an asymmetric corneal light reflex in Figure A, is presenting with strabismus. Of the answer choices, only patching the sound eye (right eye) is an appropriate treatment.

Strabismus occurs when a patient's eyes are not aligned properly. It often presents in children with one or both eyes turning inward, outward, upward, or downward. Patients will often tilt their heads or squint their eyes to correct this misalignment. Without proper treatment, there is a significant risk of developing amblyopia. Amblyopia is a developmental disorder in the visual cortex caused by abnormal visual stimuli. Untreated strabismus is the most common cause of amblyopia; it is secondary to visual loss from the deviated eye. The treatment of choice is wearing an eye patch over the appropriately tracking eye (sound eye), thereby encouraging the use of the deviated eye and preventing vision loss in this eye. Other treatments include surgical correction of strabismus, pharmacological penalization of the sound eye with atropine, and dichoptic movies and video games.

Gopal et al. discuss the pathophysiology, prevention, and therapy for amblyopia as it relates to strabismus. The authors find that the earlier clinically refractive error and strabismus are detected and treated, the greater the likelihood of preventing amblyopia. The authors recommend treating amblyopia with the correction of refractive errors, patching, and pharmacologic treatments.

Figure/Illustration A shows displacement of the light reflex from the center of the pupil in this patient's right eye, as indicated by the black arrow. This is known as an asymmetric corneal light reflex and is seen in strabismus.

Incorrect Answers:
Answer A: Brain MRI is part of the initial workup for retinoblastoma. Retinoblastoma typically presents in early childhood with visual loss, leukocoria, and an abnormal red reflex, which this patient does not have.

Answer B: Head CT in a pediatric patient could be used to rule out hemorrhage following blunt head trauma. This patient has not experienced head trauma and has no symptoms of traumatic brain injury (abnormal neurologic exam, loss of consciousness seizures). CT scans are not preferred in pediatric patients to avoid radiation exposure.

Answer C: Patching the left eye (the inappropriately tracking eye) would not treat this patient's strabismus and would likely increase his risk for amblyopia due to further decreasing his visual stimuli in this eye.

Answer E: The Bielschowsky head tilt test is used to help diagnose trochlear nerve (CN IV) palsy. Patients with a unilateral trochlear nerve and subsequent superior oblique palsy experience double vision when tilting their head to one side, which is improved by tilting the head towards the shoulder on the unaffected side. A trochlear nerve palsy typically presents with difficulty looking down and a head tilt away from the side of the lesion, unlike this patient who appears to have a visual acuity deficit.

Bullet Summary:
Patching the appropriately aligned eye is the treatment of choice for strabismus to prevent progression to amblyopia.