Patients with non-arteritic anterior ischaemic optic neuropathy (NA-ION) are needed to participate in an international randomised controlled trial, using a new intra-vitreal treatment to protect the retinal ganglion cells.
Non-arteritic anterior ischaemic optic neuropathy (NAION) is a cause of painless visual loss, typically in patients over the age of 50 years. Unlike an embolic stroke due to an obstruction within an artery, NAION is caused by circulatory insufficiency within the very small vessels of the optic nerve head. A small cup-to-disc ratio (disc at risk) is the chief risk factor, but it is also associated with arterial hypertension, diabetes and atherosclerosis. Currently there are no randomised controlled trials to guide treatment decisions.
The condition occurs due to a lack of blood supply to part of the optic nerve. If the optic disc is swollen at the time of diagnosis, then it is referred to as anterior ischaemic optic neuropathy (AION). There are two forms of AION; non-arteritic and arteritic. Arteritic AION (A-AION) is typically associated with giant cell arteritis (GCA) in patients over 55 years old, but can be seen in other causes of vasculitis. The non-arteritic (NAION) type is associated with a small cup-to-disc ratio (disc at risk) and microvascular risk factors. AION is not the same as an embolic stroke (blood clot or cholesterol) blocking the central retinal artery.
Though it is the most common cause of non-glaucomatous optic neuropathy in those over 50, there are no randomised controlled trials to guide treatment decisions. Patients under 50 are also at risk of NAION, particularly if they have diabetes, hypertension or obstructive sleep apnea.
The use of erectile dysfunction medications, such as Viagra, is also a potential risk factor
Patients will typically present with painless, monocular vision loss affecting the upper or lower half of their vision. Often symptoms are noticed on first waking. There are no features of GCA such as temporal pain, jaw claudication or scalp tenderness. Patients may have microvascular risk factors such as hypertension, diabetes, high cholesterol or obstructive sleep apnea. The use of erectile dysfunction medications, such as Viagra, is also a potential risk factor.
Central vision may be normal or reduced. There will be a relative afferent pupillary defect. Visual field loss is usually altitudinal. The optic disc has hyperaemic swelling of the sector corresponding to the visual field loss. Pale swelling or associated arteriolar occlusion must raise concerns of giant cell arteritis. The contralateral optic disc is small and crowded, with a cup-to-disc ratio of <0.2, known as a “disc at risk”.
There is no treatment, shown to improve vision or prevent NA-AION in the fellow eye, in randomised controlled trials. Overall about 40 per cent of patients will have some improvement in visual acuity or visual fields, without any treatment. There is one study showing that oral prednisolone may improve the chance of some recovery. However, in this unmasked single observer study, patients given treatment were less likely to be those with diabetes and may have had a better prognosis anyway. There is no evidence that glaucoma medication, blood thinners or anti-VEGF therapy improve visual outcomes.
The Neuro-Ophthalmology Research Disease Investigator Consortium (NORDIC) is leading an international randomised controlled trial, using a new intravitreal treatment to protect the retinal ganglion cells, in patients with NA-AION. Patients with suspected NA-AION, can be considered for the trial, if seen within 14 days from symptom onset. Several centres in Australia will participate in the trial including Sydney, Melbourne, Adelaide and Perth. Contact your local neuro-ophthalmologist to make a referral.