(Central lesion of the Chiasma) (290-Khurana 4rd) (35-P)LESIONS OF THE VISUAL PATHWAY1. Lesions of the optic nerve - Marked loss of vision or complete blindless on the affected side associated with abolition of the direct light reflex on the ipsilateral side and consensual on the contralateral side.Common causes - Optic atrophy, Traumatic avulsion of the optic nerve, Indirect optic neuropathy and acute optic neuritis2. Lesions through proximal part of the optic nerve - Ipsilateral blindness, contralateral hemianopia and abolition of direct light reflex on the affected side and consensual on the contralateral side, Near reflex is intact.3. Sagittal (Cental) lesions of the Chiasma - Bitemporal hemianopia and bitemporal hemianopic paralysis of the pupillary reflexes.Common causes - Suprasellar aneurysm, tumours of the pituitary glands*, Craniopharyngioma, suprasellar Meningioma, glioma of third ventricle, third ventricular dilatation due to obstructive hydrocephalus and chronic chiasmal arachnoiditis.4. Lateral chiasmal lesions - Binasal hemianopia associated with binasal hemianopic paralysis of the pupillary reflexes.Common causes are - Distension of third ventricles causing pressure on each side of the chiasma, and atheroma of the carotids or posterior communicating arteries.5. Lesions of the optic tract - in congruous homonymous, hemianopia associated with contralateral hemianopic pupillary reactions {Wernicke's reaction)Common causes are - syphilitic meningitis or gumma, TB and tumours of optic thalamus and aneurysms of superior cerebellar or posterior cerebral arteries.6. Lesion of the lateral geniculate body - homonymous hemianopia with sparing of pupillary reflexes and may end in partial optic atrophy7. Lesions of optic radiation(I) Inferior quadrantic hemianopia {Pie on the floor) - lesions of parietal lobe(II) Superior quadrantic hemianopia {Pie in the sky) lesions of the temporal lobes