## Most Common Exotropia in Children **Key Point:** Intermittent exotropia is the most common type of exotropia in children, accounting for approximately 60–70% of all exotropias and 5–10% of all strabismus cases. ### Epidemiology and Classification of Exotropias | Type | Frequency | Age of Onset | Characteristics | Management | | --- | --- | --- | --- | --- | | **Intermittent exotropia** | 60–70% of exotropias | 2–4 years | Deviation intermittent; worse at distance, fatigue, illness | Observation or surgery if progressing | | **Constant exotropia** | 20–30% of exotropias | Birth to 6 months | Continuous outward deviation | Early surgery | | **Sensory exotropia** | ~10% of exotropias | Variable | Secondary to vision loss in one eye | Treat underlying cause | | **Paralytic exotropia** | Rare | Variable | Due to cranial nerve palsy | Treat underlying cause | ### Clinical Features of Intermittent Exotropia **High-Yield:** Intermittent exotropia has the following hallmark features: 1. **Intermittent nature**: The deviation is not present all the time; the child can fuse and maintain alignment at times 2. **Distance worse**: The exodeviation is more pronounced when looking at distant objects 3. **Fatigue-related**: The deviation worsens with fatigue, illness, or decreased attention 4. **Near fusion**: At near, the child typically maintains good alignment due to increased accommodation and convergence 5. **Gradual onset**: Usually develops between 2–4 years of age ### Pathophysiology **Clinical Pearl:** Intermittent exotropia results from a mild insufficiency of the convergence mechanism or a relative excess of divergence. The child can control the deviation through effort and fusional vergence at near, but loses control at distance or when fatigued. ### Management Algorithm ```mermaid flowchart TD A[Child with exodeviation]:::outcome --> B{Deviation present all the time?}:::decision B -->|Intermittent| C[Intermittent exotropia]:::outcome B -->|Constant| D[Constant exotropia]:::outcome C --> E{Severity and progression?}:::decision E -->|Mild, stable| F[Observation + orthoptic exercises]:::action E -->|Moderate to severe or progressing| G[Surgical correction]:::action D --> H[Early surgical intervention]:::action ``` **Mnemonic:** **IEXO** = **I**ntermittent **EXO**tropia, **I**ntermittent deviation, **E**xo worse at distance, **X**-out (exo). ### Why Intermittent Exotropia is Most Common - It represents a mild form of exotropia that allows the child to maintain fusion intermittently - The prevalence of mild convergence insufficiency is higher than severe motor imbalances - It is more common in populations with lower hyperopic refractive errors (as opposed to myopic populations, where constant exotropia is more common) - The intermittent nature makes it less immediately noticeable, so it may be more frequently encountered in clinical practice **Warning:** Do not confuse intermittent exotropia with constant exotropia. The key discriminator is the presence of fusion at times (intermittent) versus continuous deviation (constant). Intermittent exotropia is more common and has a better prognosis than constant exotropia. **Tip:** On examination, look for the **cover test** findings: when the cover is removed from the exotropic eye, the eye will move inward (abduct to realign) if the deviation is intermittent, demonstrating that fusion was briefly maintained. [cite:Strabismus in Pediatric Ophthalmology, Chapter on Exotropia]
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