Ziliarmuskels

Ziliarmuskels, also known as ciliary muscles, are smooth muscles located in the ciliary body of the eye. They play a central role in accommodation, the process by which the eye adjusts focus for objects at different distances.

Anatomy

The ciliary muscle consists of two main fiber layers: a circular (sphincter) layer that forms a ring around the lens and a longitudinal (meridional) layer that runs forward from the ciliary body. These muscle fibers anchor to the ciliary processes and to the zonular fibers (suspensory ligaments) that suspend the lens. When the circular fibers contract, they reduce zonular tension; contraction of the longitudinal fibers changes the overall shape and position of the ciliary body.

Function

Contraction of the circular ciliary muscle relaxes the zonular fibers, allowing the lens to become more convex and increasing its refractive power for near vision. Relaxation of the ciliary muscle increases tension on the zonules, flattening the lens for distant vision. This accommodation is coordinated with pupil constriction and gaze direction as part of the near reflex.

Innervation and regulation

Parasympathetic input from the oculomotor nerve (CN III) via the Edinger–Westphal nucleus and the ciliary ganglion stimulates ciliary muscle contraction for accommodation. Sympathetic input tends to relax the ciliary muscle, aiding distant vision. The ciliary body also contains processes that secrete aqueous humor, with muscle activity influencing outflow pathways and intraocular pressure to some extent.

Clinical relevance

With aging, the lens loses elasticity, diminishing accommodative ability and contributing to presbyopia. Understanding ciliary muscle function helps explain changes in focusing and the management of related refractive conditions.