Optic chiasm

Chiasma opticum

NervousNervesHead

View in 3D

What it is
The X-shaped crossing of the two optic nerves on the floor of the brain, just above the pituitary gland and in front of the pituitary stalk.
Function
Fibres from the nasal half of each retina cross here so that each optic tract carries the opposite visual field.
Size
About 12 mm wide, 8 mm long, 4 mm thick
Clinical note
A pituitary tumour growing upward presses on the crossing fibres first, producing loss of both outer (temporal) visual fields - bitemporal hemianopia.

Contains Optic nerve (CN II), intracranial part, Optic tract

Nearby nervous structures Abducens nerve (CN VI), Arachnoid mater, Hypothalamus, Midbrain, Oculomotor nerve (CN III), Oculomotor nerve root (CN III), Olfactory tract root (CN I), Optic tract root (CN II), Trigeminal nerve root (CN V), Trochlear nerve (CN IV)