Abstract: Objective To provide morphological evidences for visual field defects caused by the compression of optic nerves and optic chiasma by saddle area tumors. Methods 80 adult cadaveric heads were dissected to study the shapes of optic chiasma and its neighbouring hypophyses,internal carotid artery and its blood-supplying arteriolae and the surrounding areas. Results The maximum angle is 100 in anterior horn with prechiasmatic space,and the minimum angle is 40 with postfixed optic chiasma.In 88.5%of the brains,the infernal carotid artery touches the optic nerves and optic chiasma on the lower outer side. Conclusion The compression of optic nerves and optic chiasma is responsible for different types of visual field defects caused by saddle area tumors.