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Visual pathways 

Visual pathways

Chapter:
Visual pathways
Author(s):

Christopher Kennard

and Sara Ajina

DOI:
10.1093/med/9780199204854.003.240601_update_001

Update:

Optic atrophy—new sections on neuromyelitis optica, a rare but important cause of bilateral or recurrent optic neuritis, and dominant optic atrophy, an insidious slowly progressive optic neuropathy.

Cortical blindness—discussion of ‘blindsight’.

Visual field impairments—impact of driving; rehabilitation of hemianopia.

Disorders of higher visual processing—enhanced discussion of visuospatial and visuoperceptual abnormalities, including Bálint’s syndrome, and visual agnosia.

Figures—new images of the ocular fundus.

Updated on 28 Nov 2012. The previous version of this content can be found here.
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date: 27 March 2017

Visual disturbances may be caused by diseases of the optic disc, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, optic radiations, and occipital lobe of the brain, as well as other brain areas involved in complex visual processing.

Diagnosis of disturbances of the visual pathways requires both knowledge of their anatomy and physiology, and the ability to carry out a thorough neuro-ophthalmological examination which should enable (1) documentation of the character and extent of the visual disturbance, and (2) topographic localization of the lesion, so that the relevant investigative techniques, such as radiological imaging, can be appropriately requested.

Visual disturbances typically produced by particular lesions

(1) Retina—peripheral field constriction as in retinitis pigmentosa and a central field defect as in senile macular degeneration. (2) Optic nerve—‘relative afferent pupillary defect’; defect of colour vision; central scotoma or arcuate defect (lesions just prior to the chiasm produce a junctional scotoma). (3) Optic chiasm—bitemporal hemianopia. (4) Optic tract—incongruous hemianopic defects. (5) Lateral geniculate nucleus—wedge-shaped homonymous field defects. (6) Optic radiations—homonymous quadrantinopia or hemianopia depending on the extent and location of the lesion (upper quadrant, temporal lobe; lower quadrant, parietal lobe). (7) Occipital lobe of the brain—(a) striate cortex—homonymous hemianopia, sometimes with macular sparing, particularly with vascular disturbances; (b) superior or inferior bank of the striate cortex—inferior or superior altitudinal defects (respectively). (8) Extrastriate areas involved in higher visual processing—can produce a wide variety of defects, including specific loss of a visual modality such as colour (achromatopsia) or movement (akinetopsia), or visual agnosia.

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