Dictionary.net

the crossing of the optic nerves from the two eyes at the base of the brain

the crossing of the optic nerves from the two eyes at the base of the brain

The X-shaped structure formed by the meeting of the two optic nerves. At the optic chiasm the fibers from the medial part of each retina cross to project to the other side of the brain while the lateral retinal fibers continue on the same side. As a result each half of the brain receives information about the contralateral visual field from both eyes.

Optic chiasm, a flattened quadrangular body in front of the tuber cinereum and infundibulum, the point of crossing or decussation of the fibers of the optic nerves; most of the fibers cross to the opposite side, some run directly forward on each side without crossing, some pass transversely on the posterior surface between the two optic tracts, and others pass transversely on the anterior surface between the two optic nerves.