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The pupil constricts when the iris sphincter muscle is stimulated and contracts. In humans, it functions to constrict the pupil in bright light (pupillary light reflex) or during accommodation. [citation needed] In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input. [5]
The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle [2] of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells.
There are three intrisic ocular muscles: the ciliary muscle, pupillary sphincter muscle (sphincter pupillae) and pupillary dilator muscle (dilator pupillae). [1] [2] All of them are smooth muscles. [2] The ciliary muscle is attached to the zonular fibers and the zonular fibers are the suspensory ligaments of the lens. [2]
The iris (brown coloured portion of the eye) controls the size of the pupil by contracting the sphincter pupillae and dilator pupillae muscles. The sphincter pupillae is the opposing muscle of the dilator pupillae. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating. The outer border of the ...
It also changes the shape of the lens within the eye but not the size of the pupil [5] which is carried out by the sphincter pupillae muscle and dilator pupillae. The ciliary muscle, pupillary sphincter muscle and pupillary dilator muscle sometimes are called intrinsic ocular muscles [6] or intraocular muscles. [7]
When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. These muscles are sometimes referred to as intrinsic eye muscles.
Pupillary response is a physiological response that varies the size of the pupil between 1.5 mm and 8 mm, [1] via the optic and oculomotor cranial nerve. A constriction response ( miosis ), [ 2 ] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as opiates / opioids or anti-hypertension medications.
The muscles it controls are the striated muscle in levator palpebrae superioris and other extraocular muscles except for the superior oblique muscle and the lateral rectus muscle. The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion , and thus controls the sphincter pupillae muscle (affecting pupil ...