Ciliary Body

The ciliary body lies just behind the iris.  Attached to the ciliary body are tiny fiber "guy wires" called zonules.  The crystalline lens is suspended inside the eye by the zonular fibers.  Nourishment for the ciliary body comes from blood vessels which also supply the iris.  

One function of the ciliary body is the production of aqueous humor, the clear fluid that fills the front of the eye.  It also controls accommodation by changing the shape of the crystalline lens.  When the ciliary body contracts, the zonules relax.  This allows the lens to thicken, increasing the eye's ability to focus up close.  When looking at a distant object, the ciliary body relaxes, causing the zonules to contract.  The lens becomes thinner, adjusting the eye's focus for distance vision.  

With age, everyone develops a condition known as presbyopia.  This occurs as the ciliary body muscle and lens gradually lose elasticity, causing difficulty reading.