Extrinsic Muscles of The Eye

The extrinsic muscles of the eye come from the bones of the orbit and are movable due to broad tendons in the eye's tough outer surface. There are six such muscles that function to move the eye in various directions and, although any given eye movement may involve more than one of them, each muscle is associated with one primary action. The six extrinsic muscles of the eye are (1) "superior rectus," - rotates the eye upward and toward the midline, (2) "inferior rectus," - rotates the eye downward and toward the midline, (3) "medial rectus," - rotates the eye toward the midline, (4) "lateral rectus," - rotates the eye away from the midline, (5) "superior oblique," - rotates the eye downward and away from the midline, and (6) the "inferior oblique" - rotates the eye upward and away from the midline. There are two check ligaments (the lateral and medial check ligaments), which limit the movement of the lateral and medial rectus. The motor units of these eye muscles contain the smallest number of muscle fibers (5-10) of any muscle in the body. Because of this, the eyes move together so that they are aligned when looking at something. A person whose eyes are not coordinated well enough to produce this alignment is said to have "strabismus," or squint.