How Does The Human Eye Move?

The Six Orbital Eye Muscles That Govern Movement

May 27, 2009

For the human eye to function and move correctly, six muscles must work in unison to provide three-dimensional vision.

Proper functioning of the eye requires six muscles that control movement. They work together to offer a wide field of vision, allowing for up, down, left and right movements. The eye is housed in the orbit of the skull and the six muscles hold it suspended in place.

The Muscles of the Eye

How the Eye Muscles Work

The eye muscles work in pairs and movement of the eye muscle is often only a very small movement, a fraction of a degree. The muscles need to be coordinated for vision to be stereoscopic (three-dimensional vision). For example, if you look to the left, the lateral rectus muscle on the left side of your left eye contracts. At the same time, on the right side of the same eye, the medial rectus relaxes.

Which Muscles Control Which Movements

The four rectus muscles are attached at one end to a fibrous ring that encircles the optic nerve, and the other end of these muscles attaches to the sclera, midline, or widest part of the eyeball.

The superior oblique muscle attaches at one end to the optic foreman (the passage through the orbit of the eye), through the trochlea; a pulley-like structure attached to the frontal bone (the upper part of each orbit) and the other end to the top part of the eyeball.

These muscles form a ‘cone’ within the orbit. The inferior oblique muscle, however, passes under the eye, near the floor of the orbit, and is attached to the eyeball (sclera) in between the superior rectus and lateral rectus.

Eyeball Motion

Normal functioning means that both the eyes look in the same direction at the same time. When looking at an object, both eyes point to the object and the brain deciphers what it is. There are some muscular imbalances that cause the eyes to ‘vergence’ or ‘disconjugate’. This means the eyes move in opposite directions. The two types of vergence are:

This problem is known as strabismus (or heterotropia) and a person suffering from strabismus may experience double vision. Often one eye will look at an object and the other eye will point in the opposite direction. Usually, after a time, the brain learns to ignore the messages sent by the eye that is turned the wrong way, and interpret images from the ‘good’ eye.

Strabismus occurs in approximately 2% of children, or can be as a result of injury, paralyses or retinal disease. If the brain ignores the strabismic eye for a great length of time, this can result in amblyopia (dimness of sight) or ‘lazy eye’. Covering the ‘good’ eye and making the strabismic eye do all the work is how this condition is generally treated.

Campbell and Reece, 2002, Biology 6th edition, ed. Benjamin Cummings, San Francisco.

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