Exophoria
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| Exophoria | |
|---|---|
| Classification and external resources | |
| ICD-10 | H50.5 |
| ICD-9 | 378.42 |
Exophoria is a form of heterophoria in which there is a tendency of the eyes to deviate outward.[1] During examination, when the eyes are dissociated by prisms, the visual axes will appear to diverge away from one another.[2]
[edit] Prevalence
Exophoria is particularly common in infancy and childhood, and increases with age.[3]
[edit] Cause
Exophoria can be caused by several factors, which include:
- Refractive errors - distance and near deviation approximately equal.
- Divergence excess - exodeviation is more than 15 dioptres greater for distance than near deviation.
- Convergence insufficiency - near exodeviation greater than distance deviation.
These can be due to nerve, muscle, or congenital problems, or due to mechanical anomalies. Unlike exotropia, fusion is possible in this condition, causing diplopia to be uncommon.
[edit] References
- ^ Allen, Edmund Turney (1899). The science of higher prisms. Harvard University: G. K. Hazlitt 6 Co., printer. p. 39. http://books.google.com/books?id=XeIYAAAAYAAJ&pg=PA39&dq=Exophoria&hl=en&ei=XBWBTPGtDIKBlAfS3uCyDw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCwQ6AEwAQ#v=onepage&q=Exophoria&f=false.
- ^ Grosvenor, Theodore (2007). Primary Care Optometry 5th Ed. Butterworth-Heinemann. p. 224.
- ^ Freier B E, Pickwell L D (1983). "Physiological exophoria". Ophthalmic and Physiological Optics 3: 267–272.
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