In a child with intermittent exotropia, which of the following is the most common and earliest sign of progression to constant exotropia?

Explanation

## Intermittent Exotropia: Natural History and Progression **Key Point:** Intermittent exotropia is characterized by periods of normal binocular alignment (phoria) alternating with periods of manifest exotropia. Progression to constant exotropia follows a predictable pattern. ### Classification of Intermittent Exotropia | Feature | Intermittent (Early) | Constant (Late) | |---------|----------------------|-----------------| | Frequency of exotropic episodes | Occasional, often distance-dependent | Constant or nearly constant | | Fusional control | Present; patient can realign eyes | Lost; eyes remain exotropic | | Diplopia awareness | Usually absent (suppression) | May develop late | | Prognosis without treatment | Progressive | Established deviation | ### Natural Progression Pattern **High-Yield:** The natural history of untreated intermittent exotropia shows a **predictable sequence of deterioration**: 1. **Increased frequency of exotropic episodes** — episodes occur more often (from occasional to frequent) 2. **Increased duration of episodes** — episodes last longer before spontaneous realignment 3. **Loss of fusional control** — patient loses ability to voluntarily realign eyes 4. **Progression to constant exotropia** — eyes remain exotropic at all times ### Clinical Significance **Clinical Pearl:** The increase in frequency and duration of exotropic episodes is the **earliest objective sign** that the intermittent exotropia is progressing toward a constant deviation. This is why regular monitoring and timely surgical intervention are important. ### Why Diplopia Is NOT an Early Sign - Suppression (cortical inhibition of the deviated eye's image) is very effective in intermittent exotropia - Patients rarely report diplopia in the early stages - Diplopia may only appear late, if at all, due to strong suppression mechanisms **Mnemonic: FED** — **F**requency increases, **E**xotropic episodes lengthen, **D**eterioration progresses (toward constant exotropia)