Ciliary muscle

Muscle in the eye

Ciliary muscle

The upper half of a sagittal section through the front of the eyeball. (Ciliary muscle is labeled at left, near center.)
Latin	musculus ciliaris
Nerve	Oculomotor nerve
System	Visual system

The ciliary muscle is a ring of smooth muscle in the eye's middle layer, known as the uvea. It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. The ciliary muscle changes the shape of the lens within the eye, which is essential for focusing on near and distant objects.

Structure

The ciliary muscle is composed of both longitudinal and circular fibers. The longitudinal fibers are attached to the sclera and the choroid, while the circular fibers are arranged concentrically around the lens. The muscle is innervated by the oculomotor nerve, specifically the parasympathetic fibers from the Edinger-Westphal nucleus.

Function

The primary function of the ciliary muscle is to control the shape of the lens. When the ciliary muscle contracts, it releases tension on the zonular fibers, allowing the lens to become more convex, which is necessary for focusing on close objects. This process is known as accommodation. Conversely, when the ciliary muscle relaxes, the zonular fibers become taut, flattening the lens and allowing the eye to focus on distant objects.

Clinical significance

Dysfunction of the ciliary muscle can lead to various eye diseases and conditions. For instance, presbyopia is an age-related condition where the ciliary muscle loses its ability to contract effectively, resulting in difficulty focusing on close objects. Additionally, abnormalities in the ciliary muscle can affect the flow of aqueous humor, potentially leading to glaucoma.

See also

• Lens (anatomy)
• Accommodation (eye)
• Oculomotor nerve
• Aqueous humor
• Presbyopia
• Glaucoma