Iris sphincter muscle

Iris Sphincter Muscle

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Illustration of the iris sphincter muscle

The Iris Sphincter Muscle (also known as the Sphincter pupillae) is a muscle in the part of the eye called the iris. It is one of the muscles that controls the size of the pupil.

Structure

The iris sphincter muscle is a circular muscle located in the stroma of the iris, near the edge of the pupil. It is approximately 0.75 mm wide and is responsible for constricting the pupil in bright light or during accommodation.

Function

The primary function of the iris sphincter muscle is to control the size of the pupil. It constricts the pupil in response to high light intensity, a process known as miosis. This is a protective reflex to prevent damage to the retina from excessive light exposure. The muscle also constricts the pupil during the process of accommodation, which is the adjustment of the eye for near vision.

Clinical significance

Damage to the iris sphincter muscle can result in a condition known as mydriasis, which is characterized by an abnormally dilated pupil. This can occur as a result of trauma, disease, or the use of certain drugs.

See also

• Dilator pupillae muscle
• Pupil
• Iris (eye)