angle of deviation
The angle of deviation is the angle between the two visual axes when the eyes are deviated, in strabismus or in heterophoria.1 The objective angle is measured from the eye movements, for example during a cover test. The subjective angle is the angle of strabismus the patient perceives from any diplopia.2
The prism and cover test measures the objective angle. A cover moves alternately between the eyes as the patient fixates, and prism power increases until the uncovered eye no longer makes a movement of redress.3 The prism that offsets every movement of redress measures the deviation. Cyclodeviations cannot be measured this way.3
On the major amblyoscope, the examiner finds the objective angle by moving both arms and alternately flashing each target until the eye stops making fixation movements.4 With normal retinal correspondence the patient sees the two targets superimposed at that setting, so the subjective angle equals the objective angle.2,4 With anomalous retinal correspondence the two angles differ, and the difference is the angle of anomaly.2,4
More detail
In harmonious anomalous retinal correspondence the patient has single vision, so the subjective angle is zero and the angle of anomaly equals the objective angle.2,4 The objective angle under undisturbed viewing is the habitual angle of strabismus, and the larger angle found after prolonged or repeated dissociation is the total angle.2 When a horizontal and a vertical deviation occur together, the prism and cover test neutralizes the horizontal deviation first and then adds vertical prism.3
Sources (9)
- Pickwell's Binocular Vision Anomalies, Appendix (Glossary)
- Pickwell's Binocular Vision Anomalies, ch. 12
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 12
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 13
- Bhola, R. (2006) Binocular Vision. Available at: https://webeye.ophth.uiowa.edu/eyeforum/tutorials/bhola-binocularvision.htm (Accessed: 4 May 2024). secondary
- Eskridge, J.B. (1983) 'Analysis of Seven Methods of Measuring the Angle of Deviation', Optometry and Vision Science, 60(1), pp. 46–51.
- Noorden, G.K. von and Campos, E.C. (2002) Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th edn. St. Louis: Mosby.
- Repka, M.X. (2019) 'Measuring the Angle of Strabismus', Journal of Binocular Vision and Ocular Motility, 69(3), pp. 87–88.
- Rutstein, R., Daum, K. (1997) Anomalies of Binocular Vision: Diagnosis & Management, Mosby, pp. 347.
Reviewed October 2026