Intermittent exotropia: 6 management options — how do parents choose?
What is intermittent exotropia?
Intermittent exotropia refers to one eye deviating outward intermittently, rather than all the time. It often appears when a child is tired, unwell, daydreaming, or looking into the distance; when the child is alert and focused it may be undetectable. This "intermittent" nature is exactly why it is so easily overlooked. Common signs include squinting one eye shut in bright light, tilting the head when looking at things, occasional complaints of double vision, and reduced depth perception (stereopsis).
Intermittent exotropia most often appears between two and five years of age and is one of the most common types of strabismus in Hong Kong. Early detection and regular monitoring are important, because controllability can change over time.
How is it diagnosed?
The naked eye alone is not reliable. A comprehensive assessment should include: visual acuity, the angle of deviation at different distances (near and far), binocular coordination and controllability, refractive status, and a fundus examination to rule out other eye conditions. Controllability — that is, whether the child can bring the eye back into alignment on their own — is one of the key indicators that determines the direction of treatment.
Six management options
1. Observation and regular monitoring
For young children with a small angle of deviation, good controllability and normal stereopsis, immediate intervention may not be necessary. The appropriate approach is regular review, monitoring whether the frequency, angle and stereopsis are deteriorating. Observation does not mean "doing nothing" — it is a planned follow-up.
2. Refractive correction (glasses)
If the child also has myopia, hyperopia or astigmatism, accurate refractive correction in itself helps improve vision and strengthen controllability. In some cases, adjusting the lens power can help control the eye position.
3. Amblyopia treatment
If one eye has weaker vision (amblyopia), or there is suppression, methods such as patching are used first to improve the vision of the weaker eye and encourage both eyes to work together. Similar vision in the two eyes is the foundation for building binocular coordination afterwards.
4. Vision therapy
Systematic exercises are used to improve fusion, vergence control and stereopsis. For convergence insufficiency or borderline-controllability cases, vision therapy has a role — training for convergence insufficiency is supported by a randomised controlled trial (CITT).¹ But to be honest: for large-angle constant exotropia, training cannot "straighten" the eye position, and surgery is the main approach for these cases. Whether training is appropriate needs individual assessment.
5. Prism
Prism lenses can change the direction in which light enters the eye, and are used in some cases to aid control and reduce double vision or the sense of fatigue. They generally serve as a supportive or transitional measure rather than a definitive cure.
6. Surgery
When the angle of deviation is large, controllability keeps worsening, or stereopsis is affected, and non-surgical approaches are not enough to cope, an ophthalmologist may consider surgery to adjust the position or tension of the extraocular muscles. Note: surgery addresses the "hardware" (eye position), but does not automatically build the "software" (binocular coordination) — some children still need a binocular vision assessment after surgery to determine whether fusion training is needed to consolidate the results.
Signs for parents to watch for
- Frequently squinting or covering one eye in bright light or sunlight
- One eye "drifting" outward when tired, daydreaming or unwell
- Tilting the head when looking at things, with occasional complaints of double vision
- Poor judgement of distance when going down stairs or catching a ball
If any of the above persists, it is worth arranging a comprehensive binocular vision assessment, and working with an ophthalmologist where needed.
Registered Optometrist (Part I) in Hong Kong; BSc (Hons) in Optometry, The Hong Kong Polytechnic University; PhD researcher in visual neuroscience. Clinically, she has co-managed strabismus and post-operative cases together with ophthalmologists, focusing on children's binocular vision and vision therapy. Full professional profile →
- Convergence Insufficiency Treatment Trial (CITT) Study Group (2008). Randomized Clinical Trial of Treatments for Symptomatic Convergence Insufficiency in Children. Archives of Ophthalmology, 126(10), 1336–1349.
- Mohney, B. G., et al. (2013). The Long-Term Follow-up of Intermittent Exotropia. Ophthalmology. (Reference on the natural history of intermittent exotropia and timing of treatment.)