The Ocular Muscles

The globe is moved by six (extra-ocular) muscles; the medial, lateral, superior, and inferior rectus muscles, and the superior and inferior oblique muscles .

(Fig 9)

The medial rectus muscle moves the eye toward the nose, or adducts the eye. The lateral rectus muscle moves the eye horizontally to outer side, or abducts the eye. The superior rectus muscle elevates the eye primarily, whereas the inferior rectus muscle depresses the eye. The recti muscles are inserted very close to the limbus, the medial rectus lying approximately 5.5mm and the lateral rectus approximately 7mm from the limbus. The rectus muscles are not normally visible, because they are covered with conjunctiva and sub-conjunctival tissue. Because they lie on the surface of the globe they are readily accessible for muscle surgery in cases of squint where one eye turns. The superior oblique muscle functions primarily as an intorter by rotating the vertical and horizontal axis of the eye toward the nose. The inferior oblique muscle acts to extort the eye and also serves to elevate the eye. The oblique muscles are inserted behind the equator of the globe.

In the lid the levator palpebrae superioris muscle serves to elevate the lid, whereas the orbicularis oculi muscle closes the eye during winking, blinking, or forced lid closure. If the levator muscle is weak or absent, the lid droops and the condition, ptosis results.