Fig. 3-3. 1, Retinal defects (scotomata): (a) vascular-ichemic, hemorrhagic. Typical and pathognomonic altitudinal defect seen with branch arterial occlusion; appropriate for altitudinal distribution of retinal ateries. Complete blindness occurs and is associated with central retinal artery occlusion by atherosclerosis, embolism, arteritis or the arterial compression of severe papilledema. (b) Inflammatory - choroiditis, granuloma; neoplastic - primary or metastatic; mechanical - retinal tear or detachment. (c) Glaucoma - frequent selective nerve fiber bundle loss causing a crescent scotoma. 2, Loss of central (macular) visual bundle (central scotoma): (a) Demyelination - multiple sclerosis, isolated optic neurities. (b) Ischemia of optic nerve. (c) Metabolic - vitamin B12 deficiency; alcoholic - nutritional amblyopia. 3, Transection of optic nerve(monocular blindness): (a) Tumor - subfrontal (sphenoid wing meningioma, optic glioma). (b) Trauma - laceration. 4, Loss of lateral portion of optic chiasma (nasal hemianopia): mechanical compression by enlarged, atherosclerotic carotid artery; can be unilateral or bilateral. 5, Loss of the medial portion of chiasma (bitemporal hemianopsia): (a) Tumor - pituitary neoplams, most often chromphobe adenoma with suprasellar extension or suprasellar neoplasm such as craniopharyngioma. (b) Hydrocephalus with ballooning of floor of third ventricle. 6, Optic tract or lateral geniculate loss (contralateral homonymous hemianopsia) - frequently incongruous: vascular - infarction in distribution of anterior choroidal arerty. 7, monocular crescent bundle (contralateral superior monocular crescent defect): tumor, infarction or hemorrhage in the anterior temporal pole or potentially also with involvement of anterior inferior calcarine cortex. 8, Loss of temporal radiations, i.e., Meyer's loop (contralateral homonymous superior quadantanopia): tumor, infarction or hemorrhage in temporal lobe. 9, Loss of upper monocular crescent bundle (contralateral inferior monocular crescentic defect): tumor, infarction or hemorrhage in parietal lobe or anterior superior calcarine cortex. 10, Loss of parietal radiations (contralateral homonymous inferior quadrantanopia): tumor infarction or hemorrhage in lower parietal region or upper calcarine cortex. 11, Loss of total optic radiations (contralateral homonymous hemianopia, usually congruous): tumor infarction or hemorrhage in the temporo-parietal junction. 12. Loss of anterior and middle calcarine cortex (contralateral homonymous hemianopia with macular sparing: macular sparing occurs when calcarine infarction is caused by posterior cerebral artery occlusion if the middle cerebral artery supplies the posterior calcarine cortex). 13, Loss of middle and posterior calcarine cortex (contralateral homonymous hemianpoia with monocular crescent sparing): tumor infarction or hemorrhage unilaterally in calcarine cortex. 14, Loss of anterior and middle calcarine cortex bilaterally (loss of all peripheral vision with sparing of central vision - keyhole vision): parasagittal tumor bilaterally compressing both anterior and middle portions of calcarine cortex; this type of defect is more commonly seen with bilateral peripheral retinal encroachment such as progressive retinitis pigmentosa and occasionally chronic papilledema. Bilateral posterior cerebral artery occlusion may leave a similar field if middle cerebral artery collateral is adequate posteriorly. 15, Bilateral loss of posterior calcarine cortex (bilateral central visual field loss): parasagittal tumor bilaterally compressing posterior calcarine cortex; this type of defect is more comonly seen following bilateral optic nerve involvement (see 2). 16, Bilateral complete loss of calcarine cortex (cortical blindness): bilateral posterior cerebral artery occlusion, usually at or near the bifrucation from the basilar artery. This type of blindness is frequently associated with denial of visual loss (Anton syndrome), presumably a result of bilateral mesial temporal lobe ischemia-infarction. Parasagittal tumor and trauma with extensive mesial occipital calcarine compression or contusion are less common causes of cortical blindness.