视交叉为一呈长方形的神经纤维块，位于蝶骨视神经沟之后上方，第三脑室前壁和底部的交界处，构成第三脑室隐窝的向前延伸部。在脚间池前部，略呈倾斜，后缘比前缘高。在垂体上部，除其后缘之外均浸在脑脊液中。由于视神经颅内段长短不同以及汇成视交叉的角度大小不同，故其与垂体的位置关系因人而异。其横径约12mm，前后径约8mm，厚约3~5mm。若以垂体为位置对比的基点，则统计资料表明，约79%位于垂体的后上方，即轻度后置位；12%偏于垂体的前部，即轻度前置；5%极度前置，位于视交叉沟之前；4%极度后置到鞍背。视交叉与鞍背并不直接接触，两者相距5~10mm，其间隔有脚间池。

The optic chiasm or optic chiasma (Greek χίασμα, "crossing", from the Greek χιάζω 'to mark with an X', after the Greek letter 'Χ', chi) is the part of the brain where the optic nerves (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes) it is located within the brain.