Sphincter pupillae muscle
Updates to Synonym Attributes
Updates to Synonym Attributes
Updates to Synonym Attributes
Updates to Article Attributes
The sphincter pupillae is a circular ring of smooth muscle within the iris responsible for constriction of the pupil (miosis). The structure is stimulated by the parasympathetic nervous system causing the muscle to decrease in diameter as it contracts.
Gross anatomy
The sphincter pupillae is a round structure comprised of smooth muscle located within the posterior iris anterior to the pigmented epithelium 1. The structure interlocks with the surrounding stroma of the iris.
Innervation
Parasympathetic nerve fibres originating in the Edinger-Westphal nucleus travel along the oculomotor nerve before synapsing at the ciliary ganglion 2. Postganglionic fibres arrive at the sphincter pupillae via the short ciliary nerves.
Action
The muscle facilitates constriction of the pupil (miosis) in turn limiting the amount of light reaching the retina.
Clinical importance
- sphincter pupillae has a role in the accommodation and pupillary light reflexes 2
- compression of CNIII may result in compression of peripherally located parasympathetic nerve fibres that supply the sphincter pupillae causing relaxation of the muscle and dilation of the pupil (see oculomotor nerve palsy) 3
- drugs that have cholinergic effects may act to stimulate the smooth muscle of the sphincter pupillae resulting in miosis (e.g. pilocarpine, bethanechol, and metoclopramide) 1
-<p>The <strong>sphincter pupillae</strong> is a circular ring of smooth muscle within the iris responsible for constriction of the pupil (miosis). The structure is stimulated by the parasympathetic nervous system causing the muscle to decrease in diameter as it contracts. </p><h4>Gross anatomy</h4><p>The sphincter pupillae is a round structure comprised of smooth muscle located within the posterior iris anterior to the pigmented epithelium <sup>1</sup>. The structure interlocks with the surrounding stroma of the iris.</p><h4>Innervation</h4><p>Parasympathetic nerve fibres originating in the <a href="/articles/edinger-westphal-nucleus-1">Edinger-Westphal nucleus</a> travel along the <a href="/articles/oculomotor-nerve">oculomotor nerve</a> before synapsing at the <a href="/articles/ciliary-ganglion">ciliary ganglion</a> <sup>2</sup>. Postganglionic fibres arrive at the sphincter pupillae via the <a href="/articles/short-ciliary-nerves">short ciliary nerves</a>. </p><h4>Clinical importance</h4><ul>- +<p>The <strong>sphincter pupillae</strong> is a circular ring of smooth muscle within the iris responsible for constriction of the pupil (miosis). The structure is stimulated by the parasympathetic nervous system causing the muscle to decrease in diameter as it contracts. </p><h4>Gross anatomy</h4><p>The sphincter pupillae is a round structure comprised of smooth muscle located within the posterior iris anterior to the pigmented epithelium <sup>1</sup>. The structure interlocks with the surrounding stroma of the iris.</p><h4>Innervation</h4><p>Parasympathetic nerve fibres originating in the <a href="/articles/edinger-westphal-nucleus-1">Edinger-Westphal nucleus</a> travel along the <a href="/articles/oculomotor-nerve">oculomotor nerve</a> before synapsing at the <a href="/articles/ciliary-ganglion">ciliary ganglion</a> <sup>2</sup>. Postganglionic fibres arrive at the sphincter pupillae via the <a href="/articles/short-ciliary-nerves">short ciliary nerves</a>. </p><h4>Action</h4><p>The muscle facilitates constriction of the pupil (miosis) in turn limiting the amount of light reaching the <a title="Retina" href="/articles/retina">retina</a>. </p><h4>Clinical importance</h4><ul>
-</ul>- +</ul><p> </p>
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