put together by Alex Yartsev put together by Alex Yartsev: Sorry if i used your images or data and forgot to reference you. Tell me who you are. [email protected] [email protected]

Anatomy & Physiology of the Visual Pathways , their LESIONS Physiological functions: and the Commonest Causes thereof

Re tina: first place to process visual data Big Blind Spot EDGE CONTRAST : a ganglion cell will Optic nerve head suppress its neighbours when it is excited on enlargement, eg. via papilloedema its own; thus there is CONTRAST Optic Chiasm Tunnel Vision Optic Nerve does no processing of its own. Suprachiasmatic Concentric diminution Axons are myelinated after the optic nerve exits the Hypothalamus Glaucoma, papilloedema and syphilis eyeball at the back though the Lamina Cribrosa

Optic Chiasm: The NASAL retinal field Central Scotoma DECUSSATES and the TEMPORAL does NOT. Internal optic nerve The Optic nerve sends fibres to the HYPOTHALAMUS destruction, eg. optic neuritis Glaucoma, papilloedema and syphilis Unilateral Blindness Hypothalamus: Suprachiasmatic Nucleus Total loss of one field: Devoted to maintaining the CIRCADIAN RHYTHMS Tumour, retinal artery infarct, Trauma Glaucoma, papilloedema and syphilis Optic Tract: delivers all the information from the Bitemporal Hemianopia contralateral visual field to the LG. Loss of fields which cross over in Lat. Geniculate N. the chiasm : Pituitary Tumour, trauma Superior Colliculus of midbrain  Optic Tract = receives fibres before the lateral; Meyer’s Loop geniculate nucleus; involved in Homonymous Hemianopia MOTOR AVOIDANCE i.e incoming Loss of one side of perception missiles, plus SACCHADES (for Lesion is post-chiasm and smooth pursuit) and glancing at an Midbrain could be anywhere, until the lat. geniculate unexpected touch, i.e attention focus Sup.Colliculus eg. MCA infarct, tumour, Aneurism post- chiasm Pulvinar Nucleus of Thalamus is involved in focussing attention and Superior Quadrantinopia prioritising eye movements ; it Pulvinar Thalamus TEMPORAL LOBE LESION projects to the visual assoc. areas MCA lacunar infarct in Lateral Geniculate penetrating arteries, tumour… Nucleus is the FIRST Inferior Quadrantinopia PLACE where the is accurate PARIETAL LOBE LESION topographical representation MCA lacunar infarct in of what the retina sees. penetrating arteries, tumour… PLUS L.G. also sorts Optic Radiation function streams , i.e sorts the Homonymous Hemianopia colour data from edge Band of Gennari detection data, etc; Loss of one side of perception MCA infarct or tumour PLUS L.G sorts data from Calcarine Cortex each eye into its separate stream. Homonymous Hemianopia with Macular Sparing !! VERY IMPORTANT!! Pathognomic of an Both eyes’ images must be Occipital PCA infarct; superimposed for “REGISTRATION ” to WHY? The area which process information from the MACULA is happen, i.e depth perception- the largest part of the calcarine (primary visual) cortex has a DUAL the inference of where the BLOOD SUPPLY: thus any infarct here will more than likely spare

object is in space. the macula and wipe out everything else.

Meyer’s Loop =fibres to the calcarine cortex SYMPTOMS ARE STRANGE : “Blind Sighted” curve around the lateral wall of the lateral These patients are unable to process visual information, but ventricle, forming a broad sheet which sweeps still have normal circadian rhythms (the supra-chiasmatic across, covering much of the post. and inf. horns hypothalamic connection is spared) and, oddly INF VIS. FIELD = the fibres furthest parietal they will avoid incoming projectiles because the superior SUP VIS FIELD = the fibrest furthest temporally colliculus is still processing and transmitting “threat- MACULA = the broad central area identification” movement and attention-focussing information. CALCARINE CORTEX: primary visual cortex First real ANALYSIS of visual information; the cortex contains neurones which respond to various features of the image; SECONDARY VISUAL ASSOCIATION AREA: the neurons respond most strongly to edges of a particular V2 to V5 orientation. This yields a decomposition of the image according to LESIONS HERE = NO LOSS OF VISUAL FIELD: Much Worse! its edges. NOT SOMETHING YER BORN WITH: these features Loss of processing: develop in infancy; ref. them kittens who were kept in the dark from V2 OR V3 INFARCT: (posteriormost, next to the calcarine sulcus birth and went blind despite having healthy eyes. (V1)= LOSS OF ORIENTATION + Mental Rotation

SECONDARY VISUAL ASSOCIATION CORTEX: V4 INFARCT: = Loss of COLOUR in vision, monochrome SEPARATION INTO COMPUTATIONAL STREAMS: V5 INFARCT: = Loss of MOVEMENT detection, “photographic” Where is it?" stream proceeds from the superior occipital lobe through vision where only still frames are perceived the middle temporal gyrus to the parietal lobe. This stream places objects in space and detects whether they are moving, relative to their background or to other objects, or whether the background itself is moving . = ORIENTATION "What is it?" stream proceeds through the inferior occipital to the inferior temporal lobe. RECOGNITION of all the separate objects, faces, and people, which or whom we are able to recognize. COLOUR information is extracted nearby in the V4 area (temporo-occipital)