2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 1: Orbit and Ocular Adnexa
Fine Structure of the Extraocular Muscles
In the extraocular muscles, the ratio of nerve fibers to muscle fibers is very high (1:3–1:5) compared with the ratio of nerve axons to muscle fibers in skeletal muscle (1:50–1:125). This high ratio enables precise control of ocular movements. The fibers of the extraocular muscles are a mixture of (1) slow, tonic-type fibers, which are innervated by multiple grapelike nerve endings (en grappe) and are useful for smooth-pursuit movements; and (2) fast, twitch-type fibers, which have platelike nerve endings (en plaque) and aid in rapid saccadic movements of the eye.
Porter JD, Baker RS, Ragusa RJ, Brueckner JK. Extraocular muscles: basic and clinical aspects of structure and function. Surv Ophthalmol. 1995;39(6):451–484.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.