Sudden vision changes: causes, red flags and what to do

Vision can change in many ways: blurring, double vision, patches that are missing or distorted, lines or flashing lights, new floaters, a shadow or curtain across part of the field, or a complete loss of sight in one or both eyes. The NHS describes vision loss as affecting how well you see, which can gradually get worse over time or happen suddenly and can affect one or both eyes.

What matters most is speed and associated symptoms. A change that comes on over minutes to hours, or that comes with pain, headache, weakness or speech trouble, is treated as urgent. Gradual changes are still important and should be checked by an optician, but they are less likely to be an emergency.

The NHS vision loss page advises going to A&E or calling 999 if you suddenly cannot see from 1 or both eyes or suddenly have severe eye pain. It advises asking for an urgent GP appointment or getting help from NHS 111 if you have changes in your vision such as blurred vision, double vision or seeing flashing lights or shapes, a dark shadow moving across your vision, pain in 1 or both eyes, a red and painful eye, or eyes that feel painful or uncomfortable in bright light. If you think you may have vision loss without these features, it advises seeing an optician.

The NHS migraine page lists loss of vision, or blurred or double vision, among symptoms that need a 999 call if they come with a sudden extremely painful headache, problems speaking or remembering, drowsiness or confusion, a seizure, or weakness on one side. The NHS multiple sclerosis page lists sudden weakness or numbness in one arm, loss or blurring of vision and problems with balance and co-ordination as possible signs of a stroke needing urgent attention. Do not drive yourself to A&E; ask someone to drive you or call 999.

The NHS pairs symptoms with causes. Blurred or cloudy vision, halos around lights and colours looking less bright suggest cataracts in adults. Dots, lines, flashes, darkness or shadows appearing in vision, often suddenly, suggest a detached retina. A distorted area in the middle of vision with difficulty reading or seeing faces suggests age-related macular degeneration. Gradual worsening of sight in someone with diabetes suggests diabetic retinopathy. Blurred vision with severe eye pain and a red eye suggests glaucoma. It cautions that your symptoms may give you an idea of the cause but that diagnosis needs assessment.

Other causes include eye inflammation. The NHS says uveitis can cause eye pain, red or watery eyes, reduced or blurred vision, light sensitivity and flashes and floaters or dark spots, and that in some people it develops over hours and days. Nerve inflammation (optic neuritis), which is sometimes linked to multiple sclerosis, blockage of a retinal blood vessel and problems in the brain can also cause sudden visual changes.

The NHS says a detached retina is when the thin layer at the back of the eye becomes loose, that it needs to be treated quickly to stop it permanently affecting sight, and that symptoms include a sudden appearance or increase of floaters, flashes of light, a dark curtain or shadow and blurred vision. It advises getting help from NHS 111 for these symptoms. Treatment is surgery, which will usually stop vision getting worse, and options include vitrectomy, scleral buckling, a gas bubble or laser and freezing treatment for tears.

It is more likely if you are short-sighted, have had an eye operation or injury, or have a family history. The NHS also notes that you can get a detached retina more than once, so new symptoms after treatment should be reported promptly.

The NHS describes temporal arteritis, or giant cell arteritis, as inflammation of the arteries at the temples that is serious and needs urgent treatment. Symptoms include frequent severe headaches, pain or tenderness at the temples or scalp, jaw pain when eating or talking, and vision problems such as double vision or loss of vision in one or both eyes. It can lead to stroke and blindness if not treated quickly, treatment with steroids is started before the diagnosis is confirmed, and if you have vision problems you should have a same-day appointment with an eye specialist.

Migraine can also cause temporary visual disturbance. The NHS says aura symptoms can include seeing zigzag lines or flashing lights and should not last for longer than 1 hour, and that you should ask for an urgent GP appointment or call NHS 111 if aura symptoms last longer than 1 hour at a time. Anyone with a first-ever visual aura, or with aura that is different from usual, should be assessed rather than assumed to be migraine.

An optician or eye casualty team will check how well you see, examine the front and back of the eye, check eye pressure and look at your visual fields. Depending on what is found you may be referred to an ophthalmologist. The NHS says that if an optician or GP thinks vision loss is caused by a condition you will usually be referred to an eye specialist for tests and discussion of treatments, and that some conditions cause permanent vision loss that cannot be treated, in which case support and low vision services are available.

If your symptoms are due to problems in the brain or blood vessels, the assessment will include blood pressure, blood tests and often scanning, which is arranged through emergency services or a stroke or neurology team.

In the NHS, an NHS-funded sight test is available through high-street opticians for those eligible, and hospital eye casualty services handle emergencies, usually after a call to NHS 111 or a GP. Private ophthalmology is available for those who prefer it, but in an emergency go to the nearest A&E or eye casualty rather than waiting for a private slot. For permanent sight loss, the NHS describes support including low vision aids, help adapting the home and workplace, registration as sight impaired with the local authority, and the RNIB.