Overview Introduction When light passes through the lens it reaches the the retina, where the formed image is inverted and reversed for example, upper visual space information will be projected to the lower retina axons leave the retina into the optic nerve fibers pass through the optic chiasm and subsequently in the optic tract there is fiber crossing in the optic chiasm neuronal fibers from the left side of the retina (left hemi-retina) will end up in the left optic tract neuronal fibers from the right hemi-retina will end up in the right optic tract axons in the optic tracts will synapse in the lateral geniculate nucleus (LGN) of the thalamus fibers from the LGN makes it way to the visual cortex as optic radiations inferior optic radiations form the Meyer's loop which carries information from the inferior retina (and thus the superior visual field) note that these radiations pass into the temporal lobe and therefore temporal lobe lesion result in a contralateral homonymous superior quadrantopia ("pie in the sky") superior optic radiations pass by the parietal lobe and therefore lesions of the parietal lobe results in a contralateral homonymous inferior quadrantopia ("pie on the floor") optic radiations eventually synapse in the primary visual cortex superior optic radiations project to the superior bank of the calcarine fissure inferior optic radiations will project to the lower bank of the calcarine fissure Summary of conscious vision perception retina → optic nerve → optic chiasm → optic tract → lateral geniculate body → optic radiation to primary visual cortex Additional pathways retina → optic nerve → optic chiasm → optic tract → pretectal area and superior colliculus the pretectal area is important for the pupillary light reflex swinging flashlight test is used to diagnose a relative afferent pupillary defect normal both pupils constrict quickly and equally when either is exposed to direct light pupils do not change in size when light moves quickly between eyes abnormal (lesion in the afferent pathway) sensory stimulus from affected pathway to the midbrain is reduced unaffected pupil will dilate from its constricted state when light is moved from the unaffected to the affected eye common causes include unilateral optic nerve lesions and severe unilateral retinal disease the superior collicus and pretectal area is important for eye movement towards visual stimuli Common Lesions Select Visual Field Defects Visual Field Deficit Etiology Central scotoma Macular degeneration Retinal infarction hemorrhage degeneration infection Monocular vision loss Optic neuritis Anterior ischemic optic neuropathy Optic glioma Bitemporal hemianopia Pituitary adenoma Craniopharyngioma Hypothalamic glioma Contralateral homonymous hemianopia Optic tract lesions (rare) secondary to malignancy demyelination infarction Optic radiation lesions Lesion involving the entire primary visual cortex Contralateral superior quadrantanopia ("pie in the sky") Temporal lobe lesions Lesions involving the lower bank of the calcarine fissure Contralateral inferior quadrantanopia ("pie on the floor") Parietal lobe lesions such as infarction of the superior division of the middle cerebral artery Lesions involving the superior bank of the calcarine fissure Homonymous heminanopia with macular sparing Posterior cerebral artery infarction