The two optic nerves originating from nerve fibres in the retina join to form the optic chiasma. Here there is hemidecussation of nerve fibres with fibres from nasal side crossing over to opposite side Optic tracts originating from optic chiasma end in the lateral geniculate body from where fibres of optic radiation originate. Nerve fibres finally end in the occipital cortex situated above and below the calcarine fissures . Hemianopia or loss of half of visual field may be homonymous, bitemporal or binasal. Amblyopia is partial loss of sight in one or both eyes in the absence of ophthalmic or other marked objective signs. It may be unilateral or bilateral. Amaurosis is complete loss of sight in one or both eyes.