Cortical Blindness

Loss of vision from bilateral damage to the occipital cortex or its optic radiation inputs, with normal anterior segments, normal pupillary light reflexes and a normal fundus.

• Because the afferent pathway to the pretectum is intact, pupils react briskly despite complete or near complete visual loss.
• Common causes: bilateral posterior cerebral artery infarction (top of the basilar syndrome, sequential strokes), hypoxic ischaemic injury after cardiac arrest, posterior reversible encephalopathy syndrome, eclampsia, contrast induced cortical toxicity after angiography, severe hypoglycaemia, head trauma, meningo encephalitis, Creutzfeldt-Jakob disease (Heidenhain variant), MELAS, and perinatal hypoxia in children.

• Bilateral visual loss ranging from complete blackness to bilateral homonymous field defects, often with macular sparing.
• Normal pupils, normal optic discs, normal eye movements, no relative afferent pupillary defect.
• Anton syndrome: the patient denies blindness, confabulates visual descriptions and collides with objects.
• Riddoch phenomenon: preserved perception of moving stimuli in an otherwise blind field. Blindsight: unconscious localisation of stimuli without awareness.
• Visual hallucinations (Charles Bonnet type) during recovery; associated visual agnosia, alexia or prosopagnosia if occipitotemporal extension.
• Acute presentation in PRES: headache, seizures, confusion, severe hypertension.

• Confirm normal pupils, dilated fundus and optic discs to exclude anterior pathway disease. Check blood glucose immediately.
• MRI brain with diffusion weighted imaging and FLAIR: bilateral occipital infarction, PRES (vasogenic oedema posterior regions), hypoxic injury. CT is insensitive early.
• MRA or CT angiography of vertebrobasilar circulation for basilar thrombosis or stenosis.
• Visual evoked potentials are abnormal or absent; electroretinogram is normal, which proves a retinal source is excluded.
• EEG if seizures or encephalopathy suspected. CSF if infection suspected. Blood pressure, urine protein, platelets, liver enzymes if pregnant.
• Formal perimetry once the patient can cooperate, to map residual fields.

• Treat the cause urgently.
  • Basilar artery occlusion or acute stroke: intravenous alteplase 0.9 mg/kg (maximum 90 mg; 10 percent as bolus, remainder over 60 minutes) within 4.5 hours, or tenecteplase 0.25 mg/kg (maximum 25 mg) single bolus, with thrombectomy where available. Aspirin 300 mg once thrombolysis window has passed or is contraindicated, then 75 mg daily with high intensity statin (atorvastatin 40 to 80 mg nightly).
  • PRES: lower blood pressure gradually (labetalol 20 mg IV bolus then 20 to 80 mg every 10 minutes to a maximum 300 mg, or nicardipine infusion 5 mg/hour titrated by 2.5 mg/hour every 15 minutes to a maximum 15 mg/hour). Stop the offending agent (calcineurin inhibitor, chemotherapy). Seizures: levetiracetam 1 to 1.5 g IV loading.
  • Eclampsia: magnesium sulphate 4 g IV over 5 to 15 minutes then 1 g/hour for 24 hours, with antihypertensives and delivery planning.
  • Hypoglycaemia: 50 percent dextrose 50 mL IV in adults (10 percent dextrose 2 mL/kg in children).
  • Contrast induced: supportive, hydration, anticonvulsants if needed; usually resolves within 24 to 72 hours.
• Rehabilitation: scanning (compensatory) eye movement training, visual restitution training, orientation and mobility, assistive technology, certification of visual impairment.
• Counsel on prognosis: recovery is best after PRES, contrast toxicity and metabolic causes; poor after extensive bilateral infarction or hypoxic injury.