A blind spot in your vision: causes and when it is urgent

Everyone has a natural blind spot where the optic nerve leaves the eye, which the brain fills in without you noticing. A blind spot in the sense of this page is something new: a patch that is missing, blurred, dimmed or wavy, that you can notice when reading, looking at a face or covering one eye.

Doctors call this a scotoma. Where it sits matters. A patch in the middle suggests the macula, the part of the retina used for fine detail. Patches elsewhere may point to the retina, the optic nerve or the brain. Whether it is in one eye or both, and whether it is steady or comes and goes, are the first questions a clinician asks.

The NHS describes age-related macular degeneration (AMD) as a common condition that affects the middle part of your vision, usually first affecting people in their 50s. It says AMD does not cause total blindness but can make reading and recognising faces difficult.

According to the NHS, the first symptom is often a blurred or distorted area in the centre of your vision, and if it gets worse you might struggle to see anything in the middle. Straight lines may look wavy or crooked, and the NHS notes that AMD is not painful and does not change the appearance of your eyes. The Macular Society notes that tests can include an Amsler grid, which detects vision changes such as wavy or missing lines, and an optical coherence tomography scan of the retina.

The NHS adds that without treatment vision may get worse gradually over years before then worsening quickly over a few weeks or months, which is why a new central distortion should be checked rather than watched.

The MS Trust says optic neuritis causes blind spots or areas of poor vision in one eye, with the colour vision or visual field potentially severely affected, and you might also have pain when you move your eyes. It generally gets worse over a few days, peaks at around two weeks and is usually recovering by 4 to 6 weeks.

The MS Trust describes it as strongly associated with multiple sclerosis but not always a sign of it. Tests may include blood tests, MRI and visual evoked potentials. For this reason it is best seen by a doctor who can examine the nerve and arrange imaging if needed.

The NHS says a detached retina is when the thin layer at the back of the eye becomes loose and needs to be treated quickly to stop it permanently affecting sight. Symptoms include floaters, flashes of light, a dark curtain or shadow in your vision, and changes such as blurred vision.

The NHS advises getting help from NHS 111 if floaters suddenly appear or suddenly increase in number, if you get flashes of light, if a dark curtain or shadow moves across your vision, or if your vision gets suddenly blurred. A shadow that spreads from the edge towards the centre is not something to leave until the weekend passes.

The NHS describes aura as warning signs before or during a migraine attack, including problems with your sight such as seeing zigzag lines or flashing lights, numbness or tingling, feeling dizzy and difficulty speaking. It says aura symptoms should not last for longer than 1 hour.

A shimmering patch that enlarges and clears within the hour, often followed by a headache, is the typical story. The NHS advises urgent help if aura symptoms last longer than 1 hour at a time, and says to call 999 if you lose your vision or have blurred or double vision together with other warning signs such as a sudden, extremely painful headache or weakness down one side.

For a new blind spot that has not gone away, an optometrist can check your vision, visual fields and the back of the eye, and refer you on. If you have a curtain or shadow, new floaters and flashes, or sudden loss of sight, use NHS 111, an eye casualty service or A&E rather than waiting for a routine slot.

• Which eye, and what happens when you cover each in turn.

• Where in your vision the patch sits and whether it moves.

• How quickly it came on and whether it has changed.

• Pain, floaters, flashes, headache or other neurological symptoms.