A 3-year-old boy is brought to the pediatric ophthalmology clinic by his mother with a complaint of inward deviation of the right eye. The deviation is present since birth and is constant. On examination, the right eye is turned inward (esotropia). The cover test shows that when the right eye is covered, the left eye makes an outward movement to fixate. When the left eye is covered, the right eye makes an inward movement to fixate. Visual acuity is 6/9 in both eyes. There is no history of prematurity, retinopathy of prematurity, or neurological symptoms. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Infantile Esotropia ### Key Clinical Features **Key Point:** Infantile esotropia (congenital esotropia) is the most common form of strabismus in infants and young children, presenting with a constant inward deviation of one or both eyes within the first 6 months of life. ### Diagnostic Criteria Met in This Case | Feature | Finding in Case | Significance | |---------|-----------------|---------------| | **Age of onset** | Since birth (< 6 months) | Hallmark of infantile esotropia | | **Type of deviation** | Constant esotropia | Not intermittent; rules out intermittent exotropia | | **Laterality** | Unilateral (right eye) | Can be unilateral or bilateral | | **Cover test response** | Abduction movement on cover | Confirms true strabismus (not phoria) | | **Visual acuity** | Equal in both eyes (6/9) | No significant amblyopia yet | | **Associated factors** | No prematurity, ROP, or neurological signs | Rules out secondary causes | ### Differential Features **Infantile Esotropia vs. Accommodative Esotropia:** - Infantile esotropia: onset before 6 months, constant, large angle (30–60 prism diopters), **no refractive error required** - Accommodative esotropia: onset typically 18 months–3 years, triggered by hyperopia, improves with spectacle correction **Infantile Esotropia vs. Paralytic Strabismus:** - Paralytic strabismus (e.g., sixth nerve palsy) would show: - Restricted abduction of the affected eye - Diplopia (in older children) - Possible associated neurological signs - This patient has full ocular motility (implied by normal fixation) ### Management Principles **High-Yield:** Early surgical correction (by age 18–24 months) is the standard of care to prevent amblyopia and allow development of binocular vision. 1. **Immediate steps:** - Cycloplegic refraction to rule out hyperopia - Assessment of binocular vision potential - Orthoptic evaluation 2. **Surgical management:** - Bilateral medial rectus recessions or unilateral medial rectus recession with lateral rectus resection - Goal: alignment within 10 prism diopters of orthotropia 3. **Amblyopia prevention:** - Monitor for lazy eye development - Patching may be needed post-operatively if one eye becomes dominant ### Why This Is NOT Accommodative Esotropia **Clinical Pearl:** Accommodative esotropia typically presents later (18 months–3 years) and is associated with hyperopia. The patient would show improvement with spectacle correction. This patient's onset at birth rules out accommodation as the primary mechanism. ### Why This Is NOT Intermittent Exotropia Intermittent exotropia presents with outward deviation (exotropia), not inward deviation (esotropia). The direction of deviation is opposite. ### Why This Is NOT Paralytic Strabismus Paralytic strabismus from sixth nerve palsy would show restricted abduction of the affected eye and would be associated with neurological signs or history of trauma/infection. The constant, symmetric fixation pattern here suggests non-paralytic (comitant) strabismus.