heterophoria
Heterophoria is a deviation of the visual axes that appears only on dissociation, as by covering one eye or distorting its image with a Maddox rod.1 Motor fusion returns the eyes to alignment once the obstacle to fusion is removed. Heterophoria is therefore defined as a deviation kept latent by the fusion mechanism.2
Heterophoria is present in most people.1 Orthophoria is the absence of heterophoria, with the dissociated position the same as the active position.1 The deviation is named by its direction on dissociation: convergent visual axes in esophoria, divergent axes in exophoria, vertical misalignment in hyperphoria, and rotation about the visual axes in cyclophoria.1
A deviation present without any dissociation is a heterotropia, or strabismus.1,2 Unless a heterophoria is intermittent, in which case the patient may notice periodic double vision, the symptoms are mainly asthenopic and related to the visual demands made on the eyes.3
Sources (6)
- Pickwell's Binocular Vision Anomalies, ch. 1
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 8
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 16
- Rutstein, R., Daum, K. (1997). Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- A pilot study of disparity vergence and near dissociated phoria in convergence insufficiency patients before vs. after vergence therapy. (2015). PMC, 4515554. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515554/
- A look at the origins of dissociated phoria and fusional vergence range testing. (2014). PubMed, 25518285. https://pubmed.ncbi.nlm.nih.gov/25518285/
Reviewed October 2026