Pretectum

Pretectum is a structure located in the midbrain. It receives binocular input from the eyes and is involved with the pupillary light reflex.

The pretectum, after receiving binocular input, outputs to the Edinger-Westphal nucleus in the midbrain, to the Cilio-spinal nucleus (Budge), which is located in the VIII cervical and I, II thoracic vertebral segments, and to the nucleus of the posterior commissure. The Edinger-Westphal nucleus and Budge's Cilio-Spinal Nucleus project onto the ciliary ganglion, whose output controls pupillary diameter (mydriasis or myosis).

The Edinger-Westphal nucleus controls the Pupillary sphincter muscle (used in situations of bright light to reduce the exposure of the retina) and the Ciliary muscle (used for eye focusing and accommodation).

The Cilio-Spinal Nucleus controls the Pupillary dilator muscle (used in situations of dark light, to increase the exposure of the retina)