The Ciliary Muscle
The ciliary muscle is part of the ciliary body. The ciliary body along with the iris and the choroid, are pigmented tissues that form the uveal tract of the eye. (Uveitis refers to inflammation of these structures.)
One of the functions of the ciliary body is to produce aqueous humor, the fluid that fills the anterior and posterior chambers.
The ciliary muscle is involved in a focusing mechanism called accommodation.
When you change your gaze from distance to near, this muscle contracts, releasing tension on the zonules, the fibers that suspend the lens in place. As this occurs, the lens becomes more curved so that light coming from objects close to the eye is focused on the retina.
Aging changes in the muscle result eventually in presbyopia, the difficulty in focusing on materials at the reading distance that most people experience when they reach their forties. Contraction of some of the ciliary body muscle fibers can also affect the drainage channels of the eye, allowing the aqueous humor to drain out of the eye more easily.
Some eye drops used to treat glaucoma, for example, pilocarpine, lower the eye pressure by making these muscle fibers contract. Other glaucoma eyedrops lower eye pressure by suppressing the formation of aqueous humor by the ciliary body.
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