Optic Nerve Axoplasmic transport : clearance of expired organelles, structural maintainance, and energy requirements. Interruption of axoplasmic transport : ischemia, compression, inflammation. Orthograde axonal transport : away from the cell body LGN. Retrograde axonal transport : toward cell body.
Intra-orbital Optic Nerve Myelination (oligodendrocytes). 20-30 mm Long. Axons: mylein and glial cell (metabolic support at the nodes of Ranvier).
Intracranalicular Optic Nerve Within the two bases of the LWS. Medial wall of canal forms lateral wall of sphenoid sinus (can be absent !). Within canal : meninges, ophthalmic artery and sympathetic plexus. 10 mm length. Tight space ! Internal carotid artery.
Intracranial Optic Nerve Leaves the cranial end of the optic canal (medially, backwards, upwards). 4-15 m (depending on the position of chiasm). Upward 45 degree-angle. Anterior cerebral and anterior comunicating artery lie superior.
Chiasm Floor of the third ventricle. 5-10 mm above the diphragma sella and the hypophysis cerebri. 12mm wide, 8mm A-P , 4 mm thick. Important relations: 3rd ventricle, hypothalmus, pituitary stalk, sella, dorsum sellam anterior and posterior clinoid processes, cavernous sinus. Nasal fibers cross ; temporal fibers do not (53:47). Wilband’s knee.
Band atrophy From (Practical viewing of the optic disk)
Retrochiasmal Visual Pathway Lesions Bilateral. Homonymous. Complete or incomplete. Congrous or incongrous.
Optic Tract Lesions Contralateral RAPD (may be an ipsilateral afferent pupillary defect if a concomitant optic neuropathy exists) A specific form of optic atrophy (band atrophy) due to the involvement of nasal fibers (temporal field) in the contralateral eye An incongruous homonymous hemianopsia.
Optic Tract Travel around the cerebral peduncles at dorsal midbrain. Divides into lateral root LGN , and a smaller medial root pretectal area (pupillary light reflex)
Primary Visual Cortex ( V1) Upper bank and lower bank (Calcarine fissure). Inferior visual filed (upper bank) , Superior visual field (lower bank). Macular projections represented by 50%-60% of the area of the calcarine cortex. Occipital tip is for foveal vision.
Occipital cortex lesions Isolated (i.e., without other neurologic deficit)ز Congruous. Paracentral or peripheral. Complete or incomplete Macular involvement or macular sparing of the central 5 degrees may occur (occipital pole involvement).
Visual Association Areas V2: input from V1. V3: sends info to basal ganglia and midbrain. V3a: perceive motion and direction. V4 : (lingual and fusiform gyrus) color. V5 : (medial temporal visual region) speed and direction, origin of pursuit movemen. V6 : (parietal) represent “extra personal space”.
“Where” Pathway Dorsal stream (occipitoparietal): Spatial orientation ,visual guidance of movement. V1 V3 V5Parietal and superotemporal cortex. Continuation of magnocellular pathway. Simultagnosia, optic ataxia, acquired oculomotor apraxia, and hemispatial neglect.
Cortical blindness Due to bilateral occipital lobe lesions. Often misdiagnosed as functional vision loss. Stroke, severe blood loss, Eclampsia, hypertension, angiography, CO poisoning, cyclosporine.
Dyschromatopsia Bilateral occipital lobe lesions in the lingual or fusiform gyri of the medial occipital lobe (medial occipito-temporal lobe). Rarely no field defect. Unilateral involvement may cause hemidyschromatopsia.
Alexia without Agraphia Loss of ability to read but can write. Left occipital lobe and splenium of corpus callosum.
Palinopsia Persistant or recurrence of visual stimulus after it has been removed.