Eye Movements: The Extra-Ocular Muscles:

The extra ocular muscles work together to produce movements of the eyes in each of the eight cardinal directions of gaze. There are six extra ocular muscles that move the globe (eyeball) These muscles are named the superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique.

Squint refers to abnormal movements of the eyeballs through lack of co-ordination of the muscles that control their movement.

• medial rectus (MR)—moves the eye toward the nose
• lateral rectus (LR)—moves the eye away from the nose
• superior rectus (SR)—primarily moves the eye upward and secondarily rotates the top of the eye toward the nose
• inferior rectus (IR)—primarily moves the eye downward and secondarily rotates the top of the eye away from the nose
• superior oblique (SO)—primarily rotates the top of the eye toward the nose and secondarily moves the eye downward
• inferior oblique (IO)—primarily rotates the top of the eye away from the nose and secondarily moves the eye upward

Downgaze, or turning the eye downward, is primarily the work of the inferior rectus, with some contribution by the superior oblique.

Abduction, or turning the eye outward toward the ear, is primarily done by the lateral rectus. Adduction, or turning the eye inward toward the nose, is primarily done by the medial rectus. In addition, the levator palpebrae superioris muscle, which is not seen on the drawing, elevates the eyelid.