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(Descriptive Terminology:, Visual Field Deficits:, Visual Pathway:) -…
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Visual Field Deficits:
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Bitemporal Hemianopia: Loss of the outer (temporal) halves of the visual field in both eyes, typically due to a lesion at the optic chiasm.
Nasal Hemianopia: Loss of the inner (nasal) halves of the visual field in both eyes, less common and often due to a specific type of lesion at the optic chiasm.
Homonymous Hemianopia: Loss of the same half of the visual field in both eyes, often due to post-chiasmal pathway lesions (e.g., optic tract, LGN, optic radiations, or primary visual cortex).
Sectoranopia: A sector-shaped loss in the visual field, associated with LGN lesions.
Quadrantanopia: Loss of vision in one quadrant of the visual field, often due to lesions in the optic radiations or sometimes the primary visual cortex.
Homonymous Hemianopia with Macular Sparing: Loss of one half of the visual field in both eyes except for the central macula, typically due to a lesion affecting the visual cortex but sparing the macular region.
Visual Pathway:
Information from the visual fields travels through the retina, enters the optic nerve, crosses at the optic chiasm (where fibers from the nasal halves of the retina decussate), and travels down the optic tract to the lateral geniculate nucleus (LGN) of the thalamus.
LGN has six layers, with 1, 4, and 6 receiving contralateral eye inputs, and 2, 3, and 5 receiving ipsilateral eye inputs.
From the LGN, the signal travels through the optic radiations, which include the posterior limb of the internal capsule, to the primary visual cortex located around the calcarine sulcus of the occipital lobe.
Beyond the primary visual cortex, information is processed in the visual association cortices.