Anterior Ischaemic Optic Neuropathy (AION)

Anterior ischaemic optic neuropathy is sudden damage to the front part of the optic nerve caused by reduced blood supply, leading to rapid loss of vision in one eye.

Common symptoms

Sudden, painless loss of all or part of vision in one eye, often noticed on waking, with a loss of upper or lower half of the visual field and reduced colour vision.

Description

AION occurs when blood flow to the front of the optic nerve is interrupted. There are two main types. The non-arteritic form is most common and linked to risk factors such as high blood pressure, diabetes, sleep apnoea, and a crowded optic nerve head. The arteritic form is caused by giant cell arteritis and is a medical emergency.

Vision loss is typically sudden, painless, and affects one eye at a time. In the arteritic form, there may also be headaches, scalp tenderness, jaw pain while chewing, and feeling generally unwell, which should prompt urgent assessment to protect the other eye.

There is no reliable way to restore vision already lost in the affected eye, but treating the underlying cause is vital. Steroids are used urgently in giant cell arteritis, and managing cardiovascular risk factors helps protect the other eye in the non-arteritic form.