Homonymous Hemianopia

Loss of the same half of the visual field in both eyes, caused by a lesion posterior to the optic chiasm (optic tract, lateral geniculate nucleus, optic radiation, or occipital cortex). The affected field is on the side opposite to the lesion.

• Causes: stroke (about 70 to 80 percent, mostly posterior cerebral artery or middle cerebral artery territory ischaemia, and haemorrhage), traumatic brain injury, brain tumour (glioma, metastasis, meningioma), demyelination, abscess, arteriovenous malformation, posterior reversible encephalopathy syndrome, migraine aura (transient), epileptic seizure (transient), post-surgical (temporal lobectomy), and neurodegenerative disease (posterior cortical atrophy, Creutzfeldt-Jakob disease).
• Prevalence in stroke survivors about 30 percent; it is the commonest visual deficit after stroke.
• Types: complete, partial (quadrantanopia), macular sparing (occipital lobe lesion with dual blood supply from the middle cerebral artery), congruous (posterior lesions) or incongruous (anterior lesions).

• Patients may not recognise the loss and complain of bumping into things on the affected side, missing food on one half of the plate, getting lost, traffic accidents, and difficulty reading.
• Reading difficulty: right hemianopia causes difficulty finding the beginning of the next word and slow reading (left-to-right); left hemianopia causes difficulty finding the beginning of the next line.
• Associated signs by localisation: left occipital lesion with alexia without agraphia; parietal lesion with visual neglect, sensory loss, and apraxia; temporal lobe lesion with superior quadrantanopia and memory impairment; optic tract lesion with contralateral relative afferent pupillary defect.
• Preserved visual acuity and normal pupil responses (in most), normal fundus (until trans-synaptic degeneration develops months later).
• Riddoch phenomenon (perception of motion in the blind field), blindsight, and visual hallucinations in the blind field.
• Associated deficits: hemiparesis, hemisensory loss, aphasia, cognitive impairment, depression, and falls.

• Confrontation fields (finger counting, red-target comparison), formal perimetry (Humphrey 24-2 or 30-2, Goldmann), checking congruity and macular sparing, and assessment for visual neglect (line bisection, cancellation tasks) which also causes apparent field loss.
• Pupil examination, fundus, acuity, and optical coherence tomography.
• Neuroimaging: MRI brain with diffusion-weighted imaging for acute stroke (CT first for haemorrhage); contrast MRI for tumour; MR or CT angiography; EEG for epilepsy.
• Stroke work-up: blood pressure, glucose, lipids, ECG and cardiac monitoring, echocardiogram, carotid and vertebral imaging.
• Driving assessment by formal fields (binocular Esterman).

• Treat the cause: acute ischaemic stroke with intravenous alteplase 0.9 mg/kg (10 percent bolus, remainder over 60 minutes) within 4.5 hours or tenecteplase 0.25 mg/kg, endovascular thrombectomy where indicated, aspirin 300 mg then 75 mg (dual antiplatelet therapy for minor stroke short term), atorvastatin 40 to 80 mg, blood pressure control, and anticoagulation for atrial fibrillation; haemorrhage: neurosurgical care and blood pressure lowering; tumour: surgery, radiotherapy, chemotherapy; demyelination: methylprednisolone 1 g IV daily for 3 to 5 days.
• Natural recovery occurs in about 40 to 50 percent in the first 3 months (most in the first month) and rarely after 6 months; early rehabilitation should begin immediately.
• Compensatory visual rehabilitation: scanning (visual search) training with daily practice for 3 to 6 weeks, reading training, and head and eye movement strategies to look toward the blind side.
• Optical devices: Fresnel press-on prisms (30 prism dioptres, placed on the spectacle lens on the side of the hemianopia, with the base toward the blind side, or Peli prisms) for field expansion, mirrors, and reading aids (slit lamp reading cards, line markers, large print).
• Visual restitution training (stimulation of the border zone) and neuromodulation have limited evidence.
• Safety and daily living: mobility and orientation training, home safety, driving cessation (hemianopia generally does not meet the visual requirements for driving; counselling and record keeping), occupational advice, and assistive technology.
• Treat visual neglect with prism adaptation and cueing; treat depression and cognitive impairment.
• Follow-up with repeated perimetry at 3 months, 6 months, and yearly; certification of visual impairment where relevant.