The ciliary ganglion is a parasympathetic ganglion located lateral to the optic nerve, where preganglionic fibres from the oculomotor nerve (III) synapse with postganglionic fibres. The postganglionic fibres leave the ganglion to enter the back of the eye via short ciliary nerves. Parasympathetic stimulation causes pupillary constriction and contraction of ciliary muscles, the latter resulting in the lens becoming rounder. Sensory fibres (and maybe sympathetic fibres) from the naso-ciliary nerve pass through the ganglion without synapsing and also reach the eye by way of the short ciliary nerves. Some of the sympathetic neurons entering the eye cause dilation of the pupil (contraction of the dilator pupillae muscle of the iris). Some of the sensory fibres supply the cornea and are important in the corneal reflex.