Visual field defects flashcards
9 high-yield MRCP Part 1 cards from the Intellect Medicos Ophthalmology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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A pituitary adenoma compresses the chiasm from below. Which part of the visual field is lost first?
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The upper temporal quadrants (bitemporal superior quadrantanopia first).
Why? Inferior crossing fibres serve the upper fields. A craniopharyngioma pushes from above, so the lower quadrants go first.
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A parietal lobe lesion causes a contralateral homonymous ______ quadrantanopia; a temporal lobe (Meyer's loop) lesion causes a contralateral homonymous superior quadrantanopia.
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inferior
Why? Meyer's loop carries the lower retinal fibres (upper field) through the temporal lobe; parietal fibres carry the upper retina (lower field).
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A parietal lobe lesion causes a contralateral homonymous inferior quadrantanopia; a temporal lobe (Meyer's loop) lesion causes a contralateral homonymous ______ quadrantanopia.
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superior
Why? Meyer's loop carries the lower retinal fibres (upper field) through the temporal lobe; parietal fibres carry the upper retina (lower field).
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Why does an occipital lobe infarct often spare the macula?
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The macular cortex has a dual blood supply, from the posterior and middle cerebral arteries.
Why? A PCA infarct causes a contralateral homonymous hemianopia with macular sparing.
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An incongruous contralateral homonymous hemianopia localises the lesion to where?
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The optic tract.
Why? Fibres from matching points in the two eyes are not yet lined up in the tract; further back (radiations, cortex) defects become congruous.
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A bitemporal hemianopia localises the lesion to where?
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The optic chiasm.
Why? The crossing nasal retinal fibres, which carry the temporal fields, are compressed in the midline — usually by a pituitary adenoma.
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Which tumour classically compresses the chiasm from above, so the lower temporal quadrants are lost first?
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Craniopharyngioma.
Why? Superior chiasmal fibres carry the lower fields. Pituitary adenomas push from below and take the upper quadrants first.
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What is the classic cause of a binasal hemianopia?
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Compression of both sides of the chiasm, e.g. bilateral internal carotid artery aneurysms (rare).
Why? The uncrossed temporal fibres on the outer edges of the chiasm carry the nasal fields.
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What is the first-line imaging for a patient with a new bitemporal hemianopia?
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MRI of the pituitary (sellar) region with contrast.
Why? MRI shows pituitary adenomas and craniopharyngiomas and their relation to the chiasm. Check pituitary hormones and formal perimetry as well.