NAION (non-arteritic anterior ischaemic optic neuropathy): symptoms and outlook

The optic nerve is the cable that carries visual information from the eye to the brain. In non-arteritic anterior ischaemic optic neuropathy, a lack of blood flow to the front of that nerve, where it enters the eye at the optic disc, damages it and causes sudden vision loss. It is sometimes described as a stroke of the optic nerve, though it is not a stroke of the brain.

The word non-arteritic distinguishes it from arteritic anterior ischaemic optic neuropathy, which is caused by inflammation of the arteries in giant cell arteritis (temporal arteritis). That is the more dangerous cause of similar symptoms and is the main reason anyone with sudden vision loss needs same-day assessment.

Hull University Teaching Hospitals says the most common symptom is sudden vision loss in one eye, usually painless, ranging from mild to severe. Some people may also notice blurred vision, colour distortion or loss of peripheral vision. People often notice it on waking, which fits with the idea that a night-time dip in blood pressure plays a part, though this is not proven.

A typical pattern is loss of the upper or lower half of the visual field in one eye. Pain on eye movement is unusual and points towards a different cause such as optic neuritis.

The exact cause is not fully understood. Hull says it happens more often in patients born with small optic discs, often referred to as a crowded disc or a disc at risk, which makes the nerve more vulnerable to blood supply problems. Some researchers have suggested transient fluctuations in blood pressure may play a role, but this is controversial.

Other risk factors listed by Hull include the chronic vascular effects of high blood pressure, diabetes, high cholesterol, sleep apnoea and smoking, and a recent drop in blood pressure, which can relate to the night-time drop while asleep or use of erectile dysfunction medicines such as Viagra.

Sudden loss of vision in one eye needs same-day assessment, through an eye casualty department, an urgent optometrist referral or A&E. The NHS lists loss of sight in one or both eyes among stroke symptoms and says to call 999 if you think you are having a stroke, including when symptoms are accompanied by face drooping, arm weakness or speech problems.

The NHS says temporal arteritis, also called giant cell arteritis, can lead to serious problems like stroke and blindness if not treated quickly, and that if you have problems with your vision you should have a same-day appointment with an eye specialist. Treatment with steroids is started before the diagnosis is confirmed because of the risk of vision loss. Symptoms to mention include headaches, scalp or temple tenderness, jaw pain while eating or talking and general illness.

Hull says NAION is diagnosed by an eye doctor, who will ask about your medical history and examine the eyes, and may arrange tests such as a visual field test and an optical coherence tomography (OCT) scan. Typically the front of the optic nerve looks swollen in the early weeks and later becomes pale.

Blood tests, including inflammatory markers, are used alongside the examination to exclude giant cell arteritis, particularly in people over 50 or with suggestive symptoms. A GP or hospital team may also check blood pressure, diabetes, cholesterol and sleep apnoea risk because these affect prevention.

Hull says there is no cure for NAION, but there are measures that can help to prevent similar attacks in the future. These are practical, and mainly concern the vascular risk factors and avoiding large drops in blood pressure.

Hull says the prognosis is variable. Some people may experience some improvement in vision in the initial period, but many others may not experience significant improvement. People with NAION in one eye are at increased risk in the other, with about a 15% risk of second eye involvement within 5 years.

Low vision services and the eye clinic can advise about aids, and the DVLA sets standards for vision that apply if you drive. Mood, especially after sudden sight loss, deserves attention too.

On the NHS the route is a same-day referral to an eye casualty or ophthalmology department, then follow-up in a neuro-ophthalmology or general ophthalmology clinic. Your GP will usually review blood pressure, diabetes and cholesterol.

Some people also see a private ophthalmologist or neuro-ophthalmologist for a second opinion. The key tests and risk-factor measures are the same; the most important thing is that suspected giant cell arteritis is not delayed by choosing between providers.