exophoria
Exophoria is a tendency of the eyes to deviate outward if fusion is blocked.1 A slight phoria is present in most normal people and is overcome by the fusion reflex.1
If fusion cannot control the imbalance, the exophoria is called decompensating and often causes asthenopia or diplopia.1 On the uncover test, the eye that was covered makes an inward (adducting) recovery movement as the cover comes off.1
The average near phoria shifts toward exophoria from the early 20s and reaches about 6 prism diopters of exophoria by about age 60.2 The reading addition does not seem to cause this physiological exophoria, and elderly patients often have decompensated exophoria at near.2
More detail
The Duane-White classification sorts exophoria into four types.2 Convergence weakness exophoria decompensates at near but not at distance, where a smaller exophoria stays compensated.2 Divergence excess is typically an intermittent divergent strabismus at distance with a compensated exophoria at near.2 Basic exophoria is about the same at every fixation distance.2 Convergence insufficiency, an inability to sustain enough convergence for comfortable near vision, is grouped with these conditions although it is strictly a convergence anomaly.2
Sources (5)
- Kanski, Clinical Ophthalmology (2024), ch. 18
- Pickwell's Binocular Vision Anomalies, ch. 8
- Rutstein, R., Daum, K. (1997). Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- Scheiman, M., Wick, B. (2014). Clinical Management of Binocular Vision: Heterophoric, Accommodative, and Eye Movement Disorders. 4th ed., Lippincott Williams & Wilkins.
- Caloroso, E.E., Rouse, M.W. (1993). Clinical Management of Strabismus. Butterworth-Heinemann.
Reviewed October 2026