Fibres of optic nerve originate from nerve fibre layer of the retina. It has intraocular, intraorbital, intracanalicular and intracranial parts. Optic disc represents the optic nerve head. Depression in the central one third is the physiological cup. Papilloedema is an oedema of the disc due to increased intracranial pressure. Anterior ischemic optic neuropathy is local anoxia of the anterior optic nerve. Optic neuritis may be acute (papillitis, retrobulbar neuritis, neuroretinitis) or chronic (toxic amblyopia). Papillitis is acute inflammation of the optic nerve head associated with rapid loss of vision. Retrobulbar neuritis is inflammation of the optic nerve situated behind the eyeball. Optic nerve may be damaged by exogenous poisons like tobacco and ethyl alcohol resulting in toxic amblyopia. Optic atrophy may be primary, secondary, consecutive, postneuritic, ischemic, toxic or glaucomatous. Optic disc is pale with loss of visual acuity and visual field defects.