<P> The parasympathetic innervation of the ciliary body is the most clearly understood . Presynaptic parasympathetic signals that originate in the Edinger - Westphal nucleus are carried by cranial nerve III (the oculomotor nerve) and travel through the ciliary ganglion . Postsynaptic fibers from the ciliary ganglion form the short ciliary nerves . Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle . The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book . </P> <P> The ciliary body is also known to receive sympathetic innervation via long ciliary nerves . When test subjects are startled, their eyes automatically adjust for distance vision . </P> <P> The ciliary body has three functions: accommodation, aqueous humor production and resorption, and maintenance of the lens zonules for the purpose of anchoring the lens in place . </P> <P> Accommodation essentially means that when the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects . When it relaxes, it flattens the lens, generally improving the focus for farther objects . </P>

Accommodation and aqueous production are a function of the