What is Optic Chiasma

 This structure makes upto portion of the anterior inferior floor of the third ventricle. It is shaped like a flat oblong bridge and connects the optic nerves and optic text. The optic chiasma is richly vasculmizcd and is approximately 8 mm long, 12 mm wide and 4mm thick. In 80 percent of cases the optic chiasma lies over the diaphragma sellae (centralchiasma). Macular projects are located centrally in optic nerve and nialte up 80-90 per cent of the total voluine of Lhe optic nerve and the chiasma fibres. Nasal mascular fibres cross in the posterior portion of the chiasma.