TOPICAL DIAGNOSIS OF RETROCHIASMAL VISUAL FIELD DEFECTS
Abstract:
Unilateral lesions of the visual sensory pathway beyond the optic chiasm - the optic tract, lateral geniculate body, optic radiation, or striate cortex - produce homonymous visual field defects without loss of visual acuity. Homonymous defects in the visual fields develop slowly when they are caused by compression and rapidly when they are caused by haemorrhage, ischemia, or inflammation. Compressive lesions generally cause progressive loss of visual field from the periphery of the field to the centre. Upon the decompression of the visual system, improvement typically first occurs in the central region and continues towards the periphery. Defects for coloured objects invariably appear before disturbances either for form or for black and white objects, a reason to use coloured stimuli routinely in the examination of visual fields. When homonymous visual field defects arise from vascular lesions, the onset of the field defects is sudden. Such defects include complete homonymous quadrantanopsias and hemianopias, incomplete homonymous quadrantanopsias and hemianopias with varying degrees of congruity, and homonymous paracentral scotomas. When and if improvement occurs, the central field clears first and may be followed by gradual enlargement of the peripheral fields if they have been affected.
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