anisophoria
Anisophoria is a heterophoria that differs between the two eyes. Optical anisophoria results from anisometropia, through unequal accommodative demands and unequal prismatic effects from the spectacle lenses, and essential anisophoria occurs in incomitancy.1
A wearer of an anisometropic correction who looks through matching points away from the optical centers receives unequal prismatic effects from the two lenses.2 The resulting disparities vary with eye position, so the heterophoria changes with the direction of gaze.3 The oculomotor system can adapt tonic vergence to compensate, and a wearer who fails to adapt has eyestrain as gaze shifts from one direction to another.3 Anisometropic contact lens corrections do not produce anisophoria, because the optical center of the lens stays fixed relative to the pupil during eye movements.3
More detail
Looking below the optical centers produces the vertical form of the same effect, called vertical imbalance, which is most troublesome during long periods of reading. With O.D. −7.00 D sphere and O.S. −3.00 D sphere, looking 1 cm below the optical centers induces 7.00Δ base down before the right eye and 3.00Δ base down before the left, a net 4.00Δ base down before the right eye.2
Sources (6)
- Pickwell's Binocular Vision Anomalies, Appendices (glossary)
- Brooks and Borish, System for Ophthalmic Dispensing, ch. 21
- Adler's Physiology of the Eye, ch. 36
- FRIEDENWALD, J.S. (1936) 'DIAGNOSIS AND TREATMENT OF ANISOPHORIA', Archives of Ophthalmology, 15(2), pp. 283–307. doi:10.1001/archopht.1936.00840140133009.
- Millodot, M. (2009) Dictionary of Optometry and Visual Science. 7th edn. Edinburgh: Butterworth-Heinemann.
- Rubin, M.L. (1993) Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
Reviewed October 2026