A 6-year-old girl is brought to the clinic with a history of outward deviation of the left eye that her father noticed 3 months ago. The deviation is not present all the time; it appears when the child is tired, daydreaming, or looking at distant objects. When the child is concentrating on near objects, the eyes appear straight. On examination, the left eye is deviated laterally. The cover test shows that when the left eye is covered, the right eye makes an inward movement. When the right eye is covered, the left eye makes an outward movement. Extraocular movements are full and normal. The child has no history of trauma, diplopia, or headaches. What is the most diagnosis?

Explanation

## Diagnosis: Intermittent Exotropia ### Clinical Reasoning **Key Point:** Intermittent exotropia is the most common form of exotropia in children, characterized by periodic outward deviation that is not present at all times. The deviation worsens with fatigue, inattention, and distance fixation, and improves with near fixation and concentration. ### Diagnostic Features in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Onset and duration** | 3 months ago, intermittent | Gradual onset, not constant | | **Triggering factors** | Fatigue, daydreaming, distance | Classic presentation | | **Near fixation** | Eyes appear straight | Fusional convergence intact | | **Cover test** | Outward deviation on cover | Confirms exotropia | | **Eye movements** | Full and normal | Rules out paralytic cause | | **Symptoms** | No diplopia or headaches | No neurological involvement | ### Pathophysiology **Mnemonic: FIDE — Fatigue, Inattention, Distance, Exotropia** - Intermittent exotropia results from inadequate fusional convergence amplitude - At distance, fusional demands are lower, allowing exotropia to manifest - At near, accommodation-driven convergence compensates and maintains alignment - Fatigue and inattention reduce fusional control, unmasking the deviation ### Management Algorithm ```mermaid flowchart TD A[Intermittent Exotropia]:::outcome --> B{Severity & Frequency?}:::decision B -->|Mild, infrequent| C[Observation + Orthoptic exercises]:::action B -->|Moderate to frequent| D[Consider surgical correction]:::action C --> E[Review at 6-12 weeks]:::action D --> F[Measure deviation at distance & near]:::action F --> G[Bilateral lateral rectus recession]:::action G --> H[Alignment achieved]:::outcome ``` **Clinical Pearl:** The key distinguishing feature of intermittent exotropia is that the deviation is NOT present all the time. When the child concentrates or fixates at near, the eyes can align normally due to intact fusional convergence. **High-Yield:** Intermittent exotropia is the most common form of exotropia in children. It typically requires observation initially, with surgery reserved for cases with high frequency or significant cosmetic/functional impact. [cite:Newell's Ophthalmology Ch 10]