conjugate prisms
Conjugate prisms, also called yoked prisms, are identical prisms placed before the two eyes with their bases in the same direction.1,2 A vertical pair has both bases up or both bases down, and a horizontal pair has the base out before one eye and the base in before the other.1 Prisms with matching base directions cause a version movement, in which the visual axes move together in the same direction.3
In nystagmus, yoked prisms can move both eyes toward the null point, which sharpens acuity and relieves the abnormal head posture.2 For example, a base-out prism over the right eye and an equal base-in prism over the left eye shift both eyes to the left and can relieve a right face turn.2 Conjugate prisms are probably most successful for a head posture of less than 15 degrees, and observers may notice that the eyes look deviated through them.2
A trial of oblique prisms has been advocated for A and V patterns in a symptomatic patient who refuses surgery or has medical reasons to avoid it, and good results were reported in V esodeviation.4 Prismatic treatment of A and V patterns has gained little popularity, and at least one major strabismus text does not advocate it.4
More detail
A pair of 10 prism diopter prisms with bases left reduces a 15-degree face turn to the right by about 5 degrees, and the remaining turn is probably within cosmetically acceptable limits.2 Small powers can be ground into spectacles with acceptable edge thickness if the frame eye size is small and the refractive error is slight. Fresnel prisms up to 30 prism diopters can manage moderate face turns, although acuity is somewhat degraded at higher powers.2
Sources (8)
- Pickwell's Binocular Vision Anomalies, appendices (glossary)
- Scheiman and Wick, Clinical Management of Binocular Vision, ch. 18
- Meister and Sheedy, Introduction to Ophthalmic Optics, ch. 8
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 19
- Diamond, S. (1964) 'CONJUGATE AND OBLIQUE PRISM CORRECTION', American Journal of Ophthalmology, 58(1), pp. 85–95.
- Noorden, G.K. von and Campos, E.C. (2002) Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th edn. St. Louis: Mosby.
- Pollard, Z.F. and Greenberg, M.F. (1970) 'V-Esotropia Aided by Conjugate-Oblique Prism Correction', American Journal of Ophthalmology, 70(1), pp. 116–118.
- Tamhankar, M.A. (2023) A-Pattern Esotropia and Exotropia: Background, Pathophysiology, Epidemiology, Medscape. Available at: https://emedicine.medscape.com/article/1199362-overview (Accessed: 5 May 2024). secondary
Reviewed October 2026