Posterior ischaemic optic neuropathy: sudden painless vision loss with a normal-looking optic disc

The optic nerve carries visual signals from the eye to the brain. An ischaemic optic neuropathy happens when the blood supply to part of the nerve falls too low for it to work. EyeWiki explains that in PION the affected part is the posterior (retrobulbar) segment, behind the eyeball, which is supplied by small vessels that are not easily seen.

Because the damage is behind the visible part of the nerve, the disc at the back of the eye looks normal at first. EyeWiki says PION is distinguished from AION by this normal appearance, whereas the disc is swollen in AION. This is why PION is hard to recognise and often diagnosed only after other causes are excluded.

EyeWiki describes three main types. Non-arteritic, non-surgical PION is rare and usually secondary to small-vessel disease, linked in studies to diabetes, hypertension, atherosclerosis and glaucoma, with other less common associations such as migraine, haemodialysis or head injury. Arteritic PION is seen in older people and is due to giant cell arteritis (GCA), which can involve the arteries supplying the optic nerve, and is characterised by often severe vision loss and a smaller chance of visual recovery.

Perioperative PION follows surgery under general anaesthetic. EyeWiki says patients typically discover the vision loss upon waking from the procedure, which may be many days after the operation, and that it tends to be bilateral, profound and permanent. Spinal surgery is one of the most common causes, and proposed risk factors include prolonged low blood pressure during surgery, postoperative anaemia, raised eye pressure, facial swelling and, among pre-existing factors, male sex, obesity, obstructive sleep apnoea and certain medicines. It is believed to be multifactorial.

EyeWiki lists sudden, painless vision loss that may be mild or severe, ranging from near-normal acuity to no light perception, with the vision typically falling over hours and sometimes worsening over days to weeks. Visual field defects are most often central but can also be in the upper or lower half of the field. There is usually no pain, and the front of the eye looks normal.

When PION is due to GCA there may be other features. The NHS lists frequent severe headaches, pain or tenderness at the temples or scalp, jaw pain while eating or talking, double vision or loss of vision, and general symptoms such as flu-like illness, weight loss, depression and tiredness.

Any sudden loss of vision is an emergency. Seek same-day assessment from an eye casualty or A&E, or call NHS 111 or 999 if you cannot reach one quickly. The NHS temporal arteritis page says to ask for an urgent GP appointment or get help from NHS 111 if you think you might have temporal arteritis because it can lead to 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 at a hospital eye department.

Do not wait to see whether the vision comes back. The NHS says treatment for temporal arteritis is started before the diagnosis is confirmed because of the risk of vision loss, and EyeWiki notes that in patients over 50 blood inflammatory markers help with the diagnosis of arteritic PION.

EyeWiki states that diagnosis is clinical and by exclusion: acute vision loss, optic nerve type field defect, a relative afferent pupillary defect, an initially normal disc and fundus with optic disc pallor developing at 6 to 8 weeks, and no other abnormality that could explain the loss. In older people, blood tests for ESR and CRP help identify GCA, and EyeWiki says a CRP and ESR together have high sensitivity and specificity for GCA, whereas non-arteritic PION does not give abnormal results.

MRI of the orbits and brain with diffusion-weighted sequences may show restricted diffusion in the posterior optic nerve and, as EyeWiki notes, helps rule out other causes such as compression or inflammation. Other tests such as visual evoked potentials can help distinguish PION from retrobulbar optic neuritis. The NHS says for suspected temporal arteritis the GP will arrange blood tests and a specialist referral, and tests may include an ultrasound scan of the temples or a temporal artery biopsy.

For arteritic PION, EyeWiki describes immediate intravenous and oral corticosteroids, tapered slowly once ESR and CRP are stable, with total treatment length of around 2.5 months in the studies it cites. The NHS describes the equivalent for temporal arteritis: a high dose of steroid (usually prednisolone) for a few weeks and then a lower dose for a longer period, sometimes years, with low-dose aspirin, a stomach-protecting medicine and bone protection often added. It warns not to stop steroids suddenly unless a doctor says so.

For non-arteritic PION, EyeWiki says steroid therapy is a practice option but there are no randomised trial data to make an evidence-based recommendation. For perioperative PION it says there is no established treatment option and steroids are not typically recommended, with general measures focused on addressing risk factors, such as maintaining adequate blood pressure and minimising blood loss during surgery. Control of vascular risk factors is part of long-term care.

EyeWiki says outcomes vary: arteritic PION often has severe vision loss and a smaller chance of recovery than non-arteritic PION, and perioperative PION tends to be profound and permanent. Because GCA can affect the second eye if untreated, prompt treatment protects the remaining vision.

In the NHS, care involves eye casualty or ophthalmology, rheumatology for GCA, and neuro-ophthalmology where available. Ask your eye clinic about support for sight loss. Private ophthalmology can offer imaging and opinions but sudden vision loss needs emergency pathways first.