The optic chiasma or optic chiasm is an X-shaped space, located in the forebrain, directly in front of the hypothalamus. It is crucial to vision. The left and right optic nerves decussate at the chiasm, thus creating the hallmark X-shape. Image by : https://www.instagram.com/p/CLNMRu2MnSP/?igshid=w4vuj04t9gx4