Definition

Noun: * A ring of smooth muscle surrounding the iris: The pupillary sphincter is a circular muscle located in the iris of the eye. Its primary function is to constrict the pupil (make it smaller) in response to bright light or during the eye's accommodation reflex for near vision.

Usage

The term "pupillary sphincter" is a specific anatomical term used in medical, biological, and optical contexts. * Damage to the pupillary sphincter can result in a permanently dilated pupil. * The pupillary sphincter contracts involuntarily when exposed to bright light. * The study examined the neural control of the pupillary sphincter.

Advanced Usage

• Pharmacological testing: The reaction of the pupillary sphincter to certain drugs (like pilocarpine or atropine) is used in medical diagnostics to assess autonomic nervous system function or to localize neurological lesions.
  • The lack of constriction after pilocarpine administration indicated a failure of the pupillary sphincter itself.

Variants and Related Words

• Sphincter pupillae: This is the Latin-derived anatomical name for the same muscle structure. It is synonymous with "pupillary sphincter" and is often used in formal medical literature.
• Iris sphincter muscle: Another equivalent term describing its location and function.
• Dilator pupillae: This is the antagonistic muscle to the pupillary sphincter. It is a radial muscle of the iris responsible for dilating (enlarging) the pupil.

Synonyms

• Sphincter pupillae (muscle)
• Iris sphincter muscle

Related Concepts (Not Synonyms)

• Pupil: The central opening in the iris whose size is controlled by the pupillary sphincter and dilator muscles.
• Iris: The colored part of the eye that contains the pupillary sphincter.
• Miosis: The medical term for pupil constriction, which is the action performed by the pupillary sphincter.
• Mydriasis: The medical term for pupil dilation, the action performed by the antagonistic dilator pupillae muscle.

Noun

1. a ring of smooth muscle surrounding the iris