antagonist (muscle)
An antagonist is a muscle of the same eye that moves the eye in the direction opposite to that of a given muscle, the agonist. The right lateral rectus, for example, is the antagonist of the right medial rectus.1 Antagonists act on the same eye, whereas yoke muscles act on both eyes.2
Sherrington's law of reciprocal innervation governs each pair. Increased innervation to a muscle is matched by a reciprocal decrease to its antagonist, so the lateral rectus relaxes as the medial rectus contracts and vice versa.1 The finely graded interplay between opposing muscles makes movements of the globe smooth and steady.2
Two muscles can be synergists for one movement and antagonists for another. The superior oblique and inferior rectus both depress the eye, but the superior oblique intorts and the inferior rectus extorts, so for cyclorotation they are antagonists.2 When a muscle is paralyzed, its antagonist acts unopposed. In a left lateral rectus palsy, the left medial rectus turns the left eye inward.1
More detail
Over time the unopposed antagonist of a paretic muscle overacts and later contracts.1 Co-contraction of antagonists in place of relaxation, as electromyography shows in the retraction syndrome, is considered abnormal in eye muscles, although it occurs in skeletal muscles.2 The term contralateral antagonist means the antagonist of the yoke muscle and is used for inhibitional palsy, though it is regarded as contradictory and best avoided.2 In surgery, weakening an agonist and strengthening its antagonist in the same session adds to the effect of each procedure and tends to stabilize the result.3
Sources (8)
- Kanski's Clinical Ophthalmology (2024), ch. 18
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 4
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 26
- Anatomy and Physiology of the Extraocular Muscles (2022) Kenhub. Available at: https://www.kenhub.com/en/library/anatomy/extraocular-muscles (Accessed: 4 May 2024). secondary
- Extraocular Muscles - Anatomy & Function (2022) American Academy of Ophthalmology. Available at: https://www.aao.org/bcscsnippetdetail.aspx?id=5e139d1b-2748-4bd0-b703-3bbcc1b48c94 (Accessed: 4 May 2024).
- Khurana, A.K. (2019) Comprehensive Ophthalmology. 7th edn. New Delhi: Jaypee Brothers Medical Publishers (P) Ltd.
- Noorden, G.K. von and Campos, E.C. (2002) Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th edn. St. Louis: Mosby.
- Rowe, F. (2012) Clinical Orthoptics. 3rd edn. Chichester, West Sussex: Wiley-Blackwell.
Reviewed October 2026