A 3-year-old boy is brought to the pediatric ophthalmology clinic by his mother with a complaint of inward deviation of the left eye, noticed since age 2 years. The child is otherwise healthy with normal development. On examination, the right eye is straight, and the left eye is turned inward. The cover test shows that when the right eye is covered, the left eye moves outward to fixate, and when the left eye is covered, the right eye remains steady. Visual acuity is 6/9 in both eyes. Extraocular movements are full in all directions. The horizontal deviation measures 25 prism diopters. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Concomitant Esotropia ### Key Clinical Features **Key Point:** Concomitant (non-paralytic) esotropia is characterized by: - Constant inward deviation of one or both eyes - Normal extraocular movements in all directions - Positive cover test (eye moves outward when the deviating eye is covered) - Equal deviation in all directions of gaze - Onset typically before age 6 years ### Diagnostic Criteria Met in This Case | Feature | Finding | Significance | |---------|---------|---------------| | Age of onset | 2 years | Typical for concomitant esotropia | | Eye movement | Full in all directions | Rules out paralytic strabismus | | Cover test response | Outward movement of left eye | Indicates esotropia | | Deviation magnitude | 25 prism diopters | Moderate deviation, consistent with concomitant type | | Visual acuity | 6/9 both eyes | No significant amblyopia yet | ### Pathophysiology **High-Yield:** Concomitant esotropia results from an imbalance in the extraocular muscle innervation and mechanics, NOT from cranial nerve palsy. The medial rectus is overacting relative to the lateral rectus. ### Management Approach ```mermaid flowchart TD A[Concomitant Esotropia Diagnosed]:::outcome --> B{Refractive Error?}:::decision B -->|Significant hyperopia| C[Prescribe glasses first]:::action B -->|Minimal refractive error| D[Assess response to correction] C --> E{Deviation reduced?}:::decision E -->|Yes| F[Continue glasses, monitor]:::action E -->|No| G[Surgical correction indicated]:::action D --> H[Surgery for residual deviation]:::action G --> I[Bilateral medial rectus recession or unilateral recession-resection]:::action ``` **Clinical Pearl:** In children with esotropia, always check for refractive error (especially hyperopia) before considering surgery, as glasses alone may correct the deviation. ### Why This Is Not the Other Options **Key Point:** The full extraocular movements and constant deviation rule out paralytic strabismus, which would show restricted movement and secondary deviation greater than primary deviation.