May 3rd
2009

Eye Anatomy  ⁄  Extraocular Muscles

The eyeball is situated in the orbit, the bony socket in the skull, and it rotates by means of the six extraocular muscles: lateral rectus, medial rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique.

right_eye_lateral_view

The first five muscles, except for the inferior oblique, begin in the back of the orbit near the top. These muscles then pass anteriorly, towards the eyeball, forming a divergent cone. The rectus muscles are directly fasten to the sclera. The superior oblique muscle passes along the superior-medial corner of the bony socket to the cartilaginous block, slips through the loop of the block and changes its course to cross the eye axis, then passes under the superior rectus muscle and fastens to the sclera at the superior-lateral quadrant of the eyeball.

The inferior oblique muscle begins from the inferior-medial corner of the orbit, passes across the eye axis under the inferior rectus muscle, and fastens to the sclera behind the tendon of the lateral rectus muscle.


Like skeletal muscles, the extraocular muscles are able to contract with shortening (isotonic contraction) or without shortening (isometric contraction). Eye movements are the rotations around a central rotation area, which is located 1-2 mm behind the anatomical center of the eyeball.

In the diagram, you can see the external muscles of the right eye – top view, back view and lateral view:

external_ocular_muscles1

The muscles of the eye move the eyeball in various directions by isotonic contraction. The lateral rectus muscle (1) moves the eyeball to the temple, away from the midline of the face. The medial rectus muscle (2) moves the eyeball to the nose, toward the midline of the face. The superior rectus muscle (3) moves the eyeball upward, and the inferior rectus muscle (4) moves the eyeball downward. The superior oblique muscle (5) moves the eyeball downward and outward. The inferior oblique muscle (6) moves the eyeball upward and outward.

In terms of the mass of the extraocular muscles, in decreasing order, the largest is the medial rectus, then the lateral rectus, the inferior rectus, the superior rectus, the superior oblique, and the inferior oblique, which is the smallest.

In spite of their small size, the extraocular muscles are able to exert considerable force. When the eye turns 40°, the muscles pull the eye with a force of about 45 grams. During fast eye movements, called saccadic eye movements, the muscles generate a force of about 110-130 grams.

The eye is supported by Tenon’s capsule, a thin membrane between the eyeball and the bony socket, which envelops the eyeball and allows it to move freely. The eyeball rests in Tenon’s capsule as if in a hammock. During isometric contraction of extraocular muscle, Tenon’s capsule supports the back side of the eye.

Take care of your eyes. Get rid of myopia the natural way.

Dr. A. Davydov.

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