Muscles of the eyeball

The muscles of the eyeball are a group of eight striated muscles located inside the orbit, which control the movements of the eyeball. They include four rectus muscles (dorsal, ventral, medial and lateral), two oblique muscles (dorsal and ventral), the retractor bulbi and the levator palpebrae superioris.

All these muscles originate in the apex of the orbit, around the optic canal and orbital fissure, with the exception of the ventral oblique muscle. They then project rostrally towards the eyeball, forming a cone around it and around the optic nerve. They all insert into the sclera, with the exception of the levator palpebrae superioris, which continues its course ahead of the eyeball.

The four rectus muscles are strips that gradually widen towards the eyeball. They are inserted into the sclera anterior to the equator of the eyeball by an aponeurotic blade. They surround the optic nerve and retractor bulbi, and are distinguished according to their position in the orbit:

• Dorsal rectus

• Ventral rectus

• Medial rectus

• Lateral rectus

Together, the rectus muscles enable the eyeball to move along the vertical and horizontal axes.

The oblique muscles are antagonistic, causing rotational movements on the axis of the eyeball, as well as stabilizing it. Unlike the straight muscles, which are broadly similar, the oblique muscles have very different origins, insertions and pathways.

The retractor bulbi muscle, supported by simultaneous contraction of the rectus muscles, retracts the bulb deeper into the orbit. This muscle divides into four bands and surrounds the optic nerve.

The coordinated actions of this muscle group (excluding the levator palpebrae superioris) enable precise, coordinated eye movements.