extraocular muscles

Also called EOMs, extrinsic ocular muscles, eye muscles

The six muscles that move each eye: four rectus muscles (medial, lateral, superior and inferior) and two oblique muscles (superior and inferior). The recti arise from the annulus of Zinn at the back of the orbit and insert in front of the equator; the obliques reach the globe from the front of the orbit and insert behind the equator on the temporal side^1,2.

Each muscle has one primary action in primary position and subsidiary actions that depend on where the eye is pointing. The oculomotor nerve supplies four of them, the trochlear nerve the superior oblique and the abducens nerve the lateral rectus¹. To test a muscle, the eye is placed where that muscle acts alone: about 23 degrees outward for the vertical recti and about 51 degrees inward for the obliques³.

More detail

The rectus insertions sit at increasing distances from the cornea, 5.5 mm for the medial, 6.5 for the inferior, 6.9 for the lateral and 7.7 for the superior, a pattern known as the spiral of Tillaux³. The recti pull the globe backward and toward the nose; the obliques pull it forward and toward the nose¹. Actions in primary position: the horizontal recti only adduct or abduct; the superior rectus elevates, then intorts and adducts; the inferior rectus depresses, then extorts and adducts; the superior oblique intorts, then depresses and abducts; the inferior oblique extorts, then elevates and abducts⁴. The oculomotor nerve's superior division serves the superior rectus and the levator of the lid, its inferior division the medial rectus, inferior rectus and inferior oblique¹. A seventh orbital muscle, the levator, lifts the upper lid and shares their nerve supply but not their job².