How Do Iris Muscles Work

The sphincter muscle of the iris is a circular muscle that constricts the pupil in bright light, whereas the dilator muscle of the iris expands the opening when it contracts. … As a result of inflammation, the iris sticks to the lens or the cornea, blocking the normal flow of fluid in the eye.

What controls the iris sphincter muscle?

Innervation. It is controlled by parasympathetic fibers of the muscarinic acetylcholine receptor (M3) that originate from the Edinger–Westphal nucleus, travel along the oculomotor nerve (CN III), synapse in the ciliary ganglion, and then enter the eye through the short ciliary nerves..

How does the iris constrict and dilate?

The white tissue around the iris is called the sclera. … a) When the iris sphincter muscle (green) contracts, it tightens the inner side of the iris, thus causing the pupil to constrict. b) When the iris dilator muscle (yellow) contracts, it pulls the inner side of the iris outward, thus causing the pupil to dilate.