Homonymous hemianopia

Overview

Homonymous hemianopia - loss of the same half of the visual field in both eyes simultaneously. Always indicates a lesion at or posterior to the optic chiasm.

Causes

•Stroke - most common overall; PCA territory infarct damages occipital cortex

•Tumour - primary or metastatic; compresses optic tract, radiations, or cortex

•Migraine with aura - transient homonymous hemianopia due to cortical spreading depression; fully reversible

•Trauma - traumatic brain injury involving occipital lobe; more prominent in younger patients

•AVM, demyelination (MS), abscess, encephalitis - less common

Presentation

•Bumping into objects on one side - unaware of objects from blind hemifield

•Difficulty reading - especially with right homonymous hemianopia (next word falls in blind field in left-to-right English)

•May describe vague 'blurring of one eye' rather than hemifield loss

•Visual acuity typically preserved; pupils intact with post-LGN lesions

⚠️

Patients frequently present saying 'one eye is blurred' - always test each hemifield in both eyes. Homonymous hemianopia is commonly misdiagnosed as a monocular problem, delaying urgent neuroimaging.

Investigations

🥇 First-line

•Formal visual field testing (automated perimetry, e.g. Humphrey) - documents extent of defect; confrontation testing as bedside screen

•MRI brain with contrast - investigation of choice for causative lesion (stroke, tumour, demyelination, AVM)

🏆 Gold standard

•MRI brain with DWI - most sensitive for acute ischaemic stroke within hours of onset

•Acute alternative: CT brain - if MRI unavailable/contraindicated; identifies haemorrhage rapidly

•Vascular imaging: CT/MR angiography - for AVM, aneurysm, or posterior circulation stroke with large vessel occlusion

Differential diagnosis

•Bitemporal hemianopia - chiasmal compression (pituitary adenoma, craniopharyngioma); crossing nasal fibres affected

•Monocular visual field loss - pre-chiasmal lesion (glaucoma, optic neuritis, retinal detachment, AION)

•Altitudinal field defect - upper/lower loss; ischaemic optic neuropathy or branch retinal artery/vein occlusion

•Cortical blindness - bilateral occipital infarction (e.g. basilar artery occlusion); intact pupils and normal fundoscopy

Management

•Treat underlying cause: acute ischaemic stroke - thrombolysis with alteplase if eligible within 4.5 hours, or thrombectomy for large vessel occlusion; admit to hyperacute stroke unit

•Secondary prevention (vascular): aspirin 300 mg initially then long-term antiplatelet; statin; antihypertensive; anticoagulation if cardioembolic source

•Migraine-related: reassurance and migraine management - no specific visual field treatment needed as defect is reversible

•Rehabilitation: visual scanning training, prism glasses, occupational therapy for activities of daily living

📌

DVLA: homonymous hemianopia is a notifiable condition. The patient must stop driving immediately and inform the DVLA. Driving may only resume after formal visual field assessment confirms the required standard - binocular field of at least 120 degrees on the horizontal with no significant central 20-degree defect. Macular sparing may allow some patients to pass but must be formally documented.

Prognosis

•Migraine-related - fully reversible

•Stroke-related - some spontaneous improvement possible in first 3 months (oedema resolution, neuroplasticity); complete persistent hemianopia unlikely to resolve fully

•Tumour-related - may improve if mass effect relieved early

•Right homonymous hemianopia causes greater reading difficulty; visual rehabilitation significantly improves quality of life even without field recovery

Key anatomy

•Posterior to the chiasm, each optic tract carries information exclusively from the contralateral visual field - any post-chiasmal lesion produces a contralateral field defect in both eyes

•Inferior fibres loop through temporal lobe (Meyer's loop) before reaching occipital cortex; superior fibres pass through parietal lobe

•Primary visual cortex (V1) at occipital pole supplied by posterior cerebral artery (PCA)

Localisation

Localising the lesion by defect characteristics

Feature	Anterior (optic tract)	Posterior (occipital cortex)
Congruity	Incongruous (asymmetric between eyes)	Congruous (identical in both eyes)
Macular sparing	Absent	Present - dual PCA/MCA supply to occipital pole
RAPD	May be present (optic tract lesion)	Absent - pupillary fibres diverge before LGN
Common cause	Tumour, trauma	PCA stroke

•Superior quadrantanopia ('pie in the sky') - temporal lobe lesion (Meyer's loop)

•Inferior quadrantanopia - parietal lobe lesion