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• Optic nerve ischaemia resulting from vascular compromise commonly in the short posterior ciliary arteries.
• Primarily occurs in middle aged patients with a history of vasculopathy.
• Distinct and must be clinically differentiated from arteritic AION, an inflammatory process most commonly seen in giant cell arteritis.

Aetiology

• Risk factors: Hypertension, diabetes, smoking, obesity, sleep apnoea
• Usually occurs in patients over the age of 50.
• Disc at risk: small optic nerve head, resulting in crowding of the optic cup
• The association with sleeping is thought to be due to relative hypotension during sleep. This further reduces arterial blood flow in vessels that are already narrowed.

Clinical

• The classical presentation is of sudden onset profound visual loss after waking from sleeping.
• Marked reduction in visual acuity, though light perception in the effected eye is usually preserved
• Visual field may be compromised
• Painless loss of vision, unlike in arteritic AION (GCA).
• Fundoscopy shows peripapillary wrinkles with optic disc oedema, there may also be a contralateral disc at risk.
• Ipsilateral relative afferent pupillary defect

Investigations

• It is important to rule out arteritic AION as the absence of pain alone provides insufficient evidence to conclusively rule out an inflammatory aetiology.
• FBC, ESR, and CRP should be ordered for all patients.
• Unlike in central retinal artery occlusion, stroke workup is usually not indicated as the process is thought to be related to hypoperfusion and not embolism.

Management

• No reliable evidence exists for any effective treatment options for NAION but exclude giant cell arteritis, as above.
• Cessation of any potentially causative medications such as PDE-5 inhibitors e.g. sildenafil.
• Ongoing management of vascular risk factors such as smoking cessation advice and optimisation of diabetic control.
• Long term aspirin may be considered, particularly given the patient demographic.

Prognosis

• The visual prognosis is generally poor though there may be some minor improvement in visual acuity in the months following.
• Visual fields does not tend to recover.

References and further reading

• Online Information
• Non-arteritic anterior ischaemic optic neuropathy: cause, effect, and management, Berry S, Eye and Brain, 2017; 9: 23-28.