A 3-year-old boy is brought to the ophthalmology clinic by his mother with a complaint of inward turning of the right eye since age 2 years. On examination, the right eye is deviated medially at rest. 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. Both eyes have full extraocular movements. Visual acuity is normal in both eyes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Esotropia **Key Point:** Esotropia is an inward (medial) deviation of one or both eyes. The cover test findings are pathognomonic: when the affected eye is covered, the normal eye abducts (moves outward) to fixate; when the normal eye is covered, the affected eye adducts (moves inward) to take up fixation. ### Cover Test Interpretation The cover test is the gold standard for detecting and quantifying strabismus: - **Unilateral esotropia:** Affected eye deviated medially; normal eye abducts when affected eye is covered; affected eye adducts when normal eye is covered. - **Unilateral exotropia:** Affected eye deviated laterally; normal eye adducts when affected eye is covered; affected eye abducts when normal eye is covered. ### Esotropia Classification | Type | Age of Onset | Characteristics | Management | |------|--------------|-----------------|------------| | **Infantile (Congenital)** | < 6 months | Large angle (40–80 PD), cross-fixation, no refractive error | Early surgery (6–12 months) | | **Accommodative** | 2–3 years | Associated with hyperopia, variable angle, responds to glasses | Hyperopic correction, cycloplegic refraction | | **Non-accommodative** | Variable | Fixed angle, no refractive component | Surgery | **High-Yield:** Accommodative esotropia (most common type in this age group) is managed with full hyperopic correction after cycloplegic refraction. If angle persists despite glasses, surgery is indicated. **Clinical Pearl:** At age 3 years with recent onset (age 2), this is likely **accommodative esotropia** secondary to uncorrected hyperopia. The normal full extraocular movements and normal visual acuity rule out restrictive or neurogenic causes. ### Why This Is Esotropia, Not Other Conditions - **Exotropia** would show outward deviation and opposite cover test findings. - **Hypertropia** is vertical deviation (one eye higher than the other). - **Cyclotropia** is rotational deviation around the anteroposterior axis. ## Management Algorithm ```mermaid flowchart TD A[Esotropia diagnosed]:::outcome --> B[Cycloplegic refraction]:::action B --> C{Hyperopia present?}:::decision C -->|Yes| D[Prescribe full hyperopic correction]:::action C -->|No| E[Non-accommodative esotropia]:::outcome D --> F{Angle resolved?}:::decision F -->|Yes| G[Continue glasses, monitor]:::action F -->|No| H[Surgical correction indicated]:::action E --> H ``` **Mnemonic:** **ESOTROPIA = Eyes Shift Inward** (medial deviation).