Ischaemic Optic Neuropathy

Ischaemic optic neuropathy (ION) is infarction of the optic nerve head (anterior ION) or retrobulbar nerve (posterior ION) causing sudden, usually painless visual loss. It is the commonest acute optic neuropathy in people over 50 years.

• Non-arteritic anterior ischaemic optic neuropathy (NAION): about 90 percent of anterior cases, caused by hypoperfusion of the short posterior ciliary circulation in a crowded optic disc ("disc at risk" with a small or absent cup).
  • Risk factors: age over 50, diabetes, hypertension, hyperlipidaemia, obstructive sleep apnoea, nocturnal hypotension, smoking, phosphodiesterase type 5 inhibitor use (sildenafil, tadalafil), amiodarone, interferon, perioperative hypotension and anaemia, and cataract surgery.
• Arteritic anterior ischaemic optic neuropathy (AAION): caused by giant cell arteritis involving the posterior ciliary arteries; an emergency because of risk of bilateral blindness.
• Posterior ION: perioperative (cardiac, spinal surgery in prone position), arteritic, radiation, and severe anaemia or hypotension.

• NAION: sudden painless visual loss, noticed on waking in many, with altitudinal (inferior most common) field defect, reduced colour vision, relative afferent pupillary defect, and swollen hyperaemic optic disc often with segmental oedema and peripapillary flame haemorrhages; the disc is small with no cup in the fellow eye; the oedema resolves over 6 to 8 weeks leaving sectoral pallor. Visual acuity is variable (often 20/40 to counting fingers). The fellow eye is involved in about 15 percent within 5 years.
• AAION: more severe visual loss (often counting fingers or worse), pale chalky white swollen disc, cotton wool spots, and preceding amaurosis fugax, diplopia, jaw claudication, scalp tenderness, headache of new onset, polymyalgia rheumatica, fever, weight loss, and anorexia; fellow eye involvement within days to weeks if untreated (up to 50 to 95 percent).
• Posterior ION: normal disc at presentation with pallor developing over 4 to 6 weeks.

• Urgent ESR, CRP, platelet count, and full blood count in anyone over 50 years with ION; ESR above 50 mm/hr (age adjusted), CRP raised, thrombocytosis, and normochromic anaemia support arteritic disease.
• Temporal artery biopsy (unilateral, at least 1 to 2 cm length) or temporal artery ultrasound showing a halo sign; biopsy remains positive for several weeks after steroids (ideally within 2 weeks, up to 4 weeks), so treatment is not delayed.
• Fluorescein angiography (delayed choroidal filling in arteritic disease) and optical coherence tomography (retinal nerve fibre thickening then thinning).
• Visual fields (altitudinal), colour vision, and MRI of the brain and orbits with MRA when atypical (to exclude compression and demyelination).
• Risk factor evaluation: blood pressure (including 24-hour ambulatory), glucose and HbA1c, lipids, sleep study for obstructive sleep apnoea, carotid imaging, and drug history.
• Differential diagnosis: optic neuritis, compressive neuropathy, papilloedema, central retinal artery occlusion, and diabetic papillopathy.

• Arteritic ION (emergency; do not wait for biopsy): methylprednisolone 1 g intravenously daily for 3 days, then prednisolone 1 mg/kg orally daily (60 mg to 80 mg), tapered slowly over 12 to 24 months guided by symptoms, ESR, and CRP.
  • Add tocilizumab 162 mg subcutaneously weekly (or every 2 weeks) with a 26-week prednisolone taper in relapsing disease or to reduce steroid exposure; methotrexate 15 to 25 mg weekly is a steroid sparing alternative.
  • Aspirin 75 mg to 150 mg daily, a proton pump inhibitor (omeprazole 20 mg daily), calcium and vitamin D supplementation, bisphosphonate (alendronate 70 mg weekly), prophylaxis against Pneumocystis (trimethoprim-sulfamethoxazole 480 mg daily) if prolonged high dose, and monitoring of glucose, blood pressure, and bone density.
  • Goal is to protect the fellow eye; vision in the affected eye rarely recovers.
• NAION: no proven treatment restores vision.
  • Treat and control vascular risk factors: blood pressure, glucose, lipids (statin), stop smoking, weight loss.
  • Treat obstructive sleep apnoea with continuous positive airway pressure.
  • Avoid nocturnal hypotension: take antihypertensives in the morning rather than at bedtime and avoid over treatment.
  • Withdraw or avoid phosphodiesterase 5 inhibitors and review amiodarone and other implicated drugs.
  • Low dose aspirin 75 mg to 100 mg daily for secondary vascular prevention does not prevent fellow eye involvement but is used for vascular protection.
  • Systemic corticosteroids (for example prednisolone 60 to 80 mg daily for 2 weeks with taper) have been used with inconsistent evidence of benefit and carry risk, so use is individualised; intravitreal steroids and anti-VEGF agents are not established.
  • Counsel on the 15 percent risk to the fellow eye; low vision services.
• Perioperative ION: maintain blood pressure and haemoglobin, minimise prone surgery duration, and correct anaemia.
• Follow up: serial fields, acuity, and disc appearance at 2 weeks, 6 weeks, and 3 months; monitor the fellow eye and review risk factor control.
• Complications: permanent visual loss, optic atrophy, fellow eye involvement (especially if arteritic and untreated), and steroid toxicity.