Visual Field Defects
On this page
Direct answer
Think of the visual field as a map on which each lesion writes its own signature: monocular field loss localises in front of the chiasm (retina or optic nerve), bitemporal defects sit at the chiasm, and homonymous defects lie behind it, with congruity increasing the further back the lesion sits. A bitemporal hemianopia from inferior chiasmal compression — pituitary adenoma classically — knocks out the upper temporal quadrants first, while compression from above (craniopharyngioma) takes the lower quadrants first. Behind the chiasm, a temporal lobe lesion of Meyer's loop gives a congruous superior homonymous quadrantanopia ("pie in the sky"), a parietal lesion the inferior quadrantanopia, and an occipital cortex infarct a congruous homonymous hemianopia — often with macular sparing when the occipital pole, supplied by the middle cerebral artery, survives posterior cerebral artery occlusion.
What you must remember
- Big divide: one eye affected means prechiasmal; both eyes with respect to the vertical midline means chiasmal or retrochiasmal.
- Junctional scotoma: a lesion at the anterior chiasm damages the ipsilateral optic nerve plus the decussating Wilbrand fibres of the contralateral inferonasal retina — ipsilateral central scotoma with contralateral superior temporal defect.
- Chiasmal quadrant rules: pressure from below (pituitary adenoma) crosses the inferior chiasmal fibres first, producing upper temporal loss; pressure from above (craniopharyngioma, hydrocephalus) produces lower temporal loss first.
- Optic tract and beyond: tract lesions give incongruous homonymous hemianopia with a relative afferent pupillary defect in both eyes of the affected field (the "double" sign worth quoting); congruity rises steadily from tract to occipital cortex.
- Meyer's loop: temporal lobe — superior homonymous quadrantanopia, pie in the sky (the loop sweeps anteriorly in the temporal lobe, so temporal lobe surgery and head injury threaten the upper field).
- Parietal radiation: inferior homonymous quadrantanopia, pie on the floor, often with contralateral sensory or motor signs localising the lobe.
- Occipital cortex: congruous homonymous hemianopia; macular sparing suggests occipital cortex infarct with occipital pole sparing via middle cerebral collaterals; a homonymous hemianopic crescent indicates a lesion at the anterior occipital cortex.
- Non-neurological field signatures for contrast: glaucoma — arcuate Bjerrum scotoma and nasal step; optic neuritis — central or centrocaecal scotoma; papilloedema — enlarged blind spot; retinitis pigmentosa — ring scotoma.
Localising five defects in one clinic morning
Walk through five real consultations. A 50-year-old man bumps into doorframes on the right; confrontation shows a right homonymous hemianopia, congruous and dense. Congruity plus density point posteriorly — MRI confirms a left occipital infarct, and macular sparing on formal perimetry fits preserved occipital pole supply. A young woman after temporal-lobe epilepsy surgery struggles to see in the right upper quadrant on driving: a right superior homonymous quadrantanopia, the expected pie in the sky from Meyer's loop. A woman with galactorrhoea and amenorrhoea reports not seeing cars approach from the sides: bitemporal hemianopia with upper temporal loss on perimetry — pituitary macroadenoma pressing from below, prolactin elevated. A man with a known optic nerve drusen has an enlarged blind spot and nasal step in one eye — prechiasmal retinal-nerve-fibre loss, not a brain problem at all. And a longstanding glaucoma patient brings a Humphrey printout showing arcuate scotomas spiralling to fixation — the patterned field of nerve fibre bundle loss. Five fields, five answers, all from one rule: decide which side of the chiasm, then which side of the midline, then how congruous, and the anatomy names itself.
Where candidates slip
Three traps recur. First, quadrant-first logic: the pituitary presses from below, so the upper temporal field goes first — candidates who reverse this lose the discrimination mark against craniopharyngioma. Second, macular sparing is meaningful only in homonymous hemianopia of occipital origin; quoting it for a tract lesion is anatomically wrong. Third, congruity: an incongruous defect favours the anterior pathway (tract, early radiation) and an exquisitely congruous one favours the occipital cortex — a rule the exam uses in single-best-answer form. Viva examiners also like the functional pair: cortical blindness after bilateral occipital infarction with normal pupils and no relative afferent pupillary defect, versus the functional overlay — remember pupils react because the reflex pathway leaves the optic tract before the visual cortex.
Frequently asked questions
Which field defect does a pituitary adenoma classically produce?
Bitemporal hemianopia, with the superior temporal quadrants affected first because the inferior chiasmal crossing fibres are compressed from below.
What is a junctional scotoma?
Ipsilateral central scotoma with contralateral superior temporal field loss, from a lesion at the anterior chiasm involving the optic nerve and decussating Wilbrand fibres.
Why do temporal lobe lesions cause a superior quadrantanopia?
The inferior retinal fibres sweep through Meyer's loop in the temporal lobe, so damage there removes the superior field on the opposite side — "pie in the sky".
What does macular sparing indicate?
A homonymous hemianopia from occipital cortex infarction with the occipital pole preserved, usually by middle cerebral artery collaterals.
Which field defect is typical of glaucoma?
An arcuate (Bjerrum) scotoma with a nasal step in one eye — a nerve fibre bundle defect, prechiasmal and unrelated to the visual pathway behind it.