Biomedical Investigation of Heterophoria; Identification, Classification and Detection

Heterophoria is a clinical condition where the tendency for the eyes to deviate is kept latent by fusional reflex. It is an ocular defect in which the visual axes are directed towards the fixation but deviate in dissociation. It is also called ‘latent strabismus’. The tendency for the two visual axes of the eyes not to be directed towards the point of fixation in the absence of an inadequate stimulus. It is the relative deviation of the eyes in absence of fusional vergence or the deviation from Ortho position that occurs when binocular fusion is made impossible. Heterophoria can be classified based on the direction of deviation or the manifestation of symptoms. Fusional vergence can be deprived by occluding one eye while the other fixates a visual target. The occluded eye will presumably deviate from its initial position by an amount of light that corresponds to the heterophoria. The cross-cover test, or alternating cover test is usually employed to detect heterophoria. One eye is covered, and then the cover is moved immediately over to the other eye. With heterophoria, when the cover is moved to the other eye, the eye that has just been uncovered can be seen to move from a deviated point.