Anterior Ischaemic Optic Neuropathy

Infarction of the optic nerve head (anterior portion of the optic nerve) supplied by the short posterior ciliary arteries, causing sudden painless visual loss with optic disc swelling. It is the commonest acute optic neuropathy in adults over 50 years.

• Two forms:
  • Non-arteritic anterior ischaemic optic neuropathy (about 90 to 95 percent): incidence 2 to 10 per 100,000 over age 50. Risk factors: small crowded optic disc with a small or absent cup ("disc at risk"), hypertension, diabetes, hyperlipidaemia, sleep apnoea, nocturnal hypotension (antihypertensive timing), smoking, atherosclerosis, anaemia, and phosphodiesterase-5 inhibitors and amiodarone (association). Fellow-eye involvement in about 15 to 20 percent within 5 years.
  • Arteritic anterior ischaemic optic neuropathy (about 5 to 10 percent): caused by giant cell arteritis, an emergency, with a risk of bilateral blindness within days if untreated (fellow-eye involvement in up to 50 to 95 percent without treatment).

• Sudden painless (non-arteritic) monocular visual loss, noticed on waking in many; altitudinal or arcuate field defect (inferior most common); acuity from normal to counting fingers (about 40 percent worse than 6/60); relative afferent pupillary defect; dyschromatopsia.
• Disc: diffuse or segmental hyperaemic oedema with peripapillary flame haemorrhages and a crowded fellow disc without a cup; the oedema resolves in 6 to 8 weeks leaving segmental pallor.
• Arteritic: severe visual loss (often counting fingers or worse), pallor with chalky white swelling, cotton wool spots, and preceding transient visual loss, diplopia, headache, scalp tenderness, jaw claudication, polymyalgia, fever, malaise, and weight loss. Choroidal ischaemia on fluorescein angiography (delayed choroidal filling) is characteristic.

• Visual acuity, pupils, colour vision, fields, dilated fundus examination of both discs (cup-to-disc ratio of the fellow eye), blood pressure, and optical coherence tomography (disc oedema, later nerve fibre layer thinning).
• In everyone over 50: ESR, CRP, platelet count, and full count; ESR above 50 mm/hour, CRP above 25 mg/L, and thrombocytosis support giant cell arteritis (ESR can be normal in a minority).
• Temporal artery biopsy (at least 1.5 to 2 cm, within 2 weeks of starting steroids, ideally within 7 days) or temporal artery ultrasound ("halo" sign); positron emission tomography or MRI of the arteries when negative.
• Systemic work-up for non-arteritic disease: glucose, HbA1c, lipids, blood pressure (including 24-hour monitoring for nocturnal hypotension), full count, homocysteine, thrombophilia in patients under 50, sleep study, carotid duplex, and echocardiography.
• MRI of brain and orbits with contrast if atypical (age under 50, progressive course, pain, no disc swelling in the acute phase, or poor recovery).

• Arteritic (giant cell arteritis): treat immediately.
  • Intravenous methylprednisolone 1 g daily for 3 days (or 500 mg to 1 g daily), then prednisolone 1 mg/kg daily (60 to 80 mg), tapered slowly over 12 to 18 months guided by symptoms and CRP (reduce by 10 mg every 2 weeks to 20 mg, then 2.5 mg every 2 to 4 weeks to 10 mg, then 1 mg monthly).
  • Steroid-sparing therapy: tocilizumab 162 mg subcutaneously every week (or every 2 weeks with steroid taper), or methotrexate 15 to 25 mg weekly.
  • Aspirin 75 to 150 mg daily, proton pump inhibitor, calcium and vitamin D, bisphosphonate, vaccination, and monitoring of glucose, blood pressure, and infection.
  • Aim: prevent the other eye from being affected; vision in the affected eye seldom recovers.
• Non-arteritic: no proven treatment. Manage risk factors (blood pressure, diabetes, lipids with statin, stop smoking, treat sleep apnoea with continuous positive airway pressure, correct anaemia), avoid nocturnal hypotension (take antihypertensives in the morning), stop phosphodiesterase-5 inhibitors and amiodarone where possible, and consider aspirin 75 to 100 mg for vascular risk (no proven effect on second-eye risk).
• Oral steroids (prednisolone 60 to 80 mg daily for 2 weeks, tapered) are used by some for early disease but evidence is limited; intravitreal agents are not recommended.
• Low-vision support, driving advice, and annual assessment.
• Prognosis: spontaneous improvement of 3 or more lines in about 40 percent of non-arteritic cases; recurrence in the same eye is rare.