ABSTRACT
Crossed and uncrossed retinal nerve fibres begin to separate at the termination of the optic nerve at the anterior angle of the optic chiasm. The blood supply to the optic chiasm is from an anastomosis of arterioles from the Circle of Willis. Lesions that compress the optic chiasm include aneurysms, craniopharyngiomas, distension of the third ventricle in obstructive hydrocephalus, optic nerve and chiasmal gliomas and pituitary tumours. Meningiomas that involve the optic chiasm may arise from the olfactory groove, tuberculum sellae or lesser wing of sphenoid and are slow growing. Pituitary adenoma is the most common intracranial tumour to involve the optic chiasm. A dilatation of an internal carotid aneurysm may cause lateral compression of the optic chiasm. Associated ocular signs and symptoms include hemifield slide, postfixation blindness, extraocular muscle palsies, optic atrophy, pallor, diplopia and oscillopsia. In addition to assessment of visual fields in patients with optic chiasm lesions, fundus examination is an important part of the ophthalmic investigation.
