Pupillary sphincter

Pupillary Sphincter

The pupillary sphincter, also known as the sphincter pupillae muscle, is a muscle in the human eye that controls the size of the pupil. It is a ring-shaped band of smooth muscle fibers located in the iris of the eye.

Function

The primary function of the pupillary sphincter is to constrict the pupil in response to bright light, a process known as miosis. This is part of the pupillary light reflex, which is an involuntary response that helps to protect the retina from excessive light that could potentially cause damage.

The pupillary sphincter is controlled by the parasympathetic nervous system, specifically the oculomotor nerve. When this nerve is stimulated, it causes the pupillary sphincter to contract, reducing the size of the pupil and limiting the amount of light that enters the eye.

Clinical significance

Abnormalities in the function of the pupillary sphincter can lead to a variety of conditions. For example, damage to the oculomotor nerve can result in a dilated pupil, a condition known as mydriasis. This can be a sign of a number of medical conditions, including stroke, brain tumor, or aneurysm.

In addition, certain drugs can affect the function of the pupillary sphincter. For example, opioids can cause miosis, while drugs such as atropine can cause mydriasis.

See also

• Pupil
• Iris (eye)
• Pupillary light reflex
• Oculomotor nerve