These visual disturbances are usually nothing to worry about, but sometimes they mean there’s a more serious sight problem. It’s important to know when to get your symptoms checked out.
Flashes and floaters are usually caused by changes to the jelly-like substance inside your eye, called the vitreous humour. As you get older, it shrinks, pulling on the retina – the layer at the back of your eye that contains light-sensitive cells. This pulling action sends signals to the optic (seeing) nerve, causing symptoms such as floaters and flashing lights in your eyes.
This is usually harmless and is more likely if you're:
Other causes of flashes and floaters can include:
Posterior vitreous detachment
This is when the vitreous humour, the jelly-like substance inside your eye, pulls away from your retina, the ‘seeing’ part of your eye. This is due to natural age-related changes. It’s usually harmless but it can cause your retina to tear or become detached from the back of your eye. This can cause loss of sight.
If your retina detaches from the back of your eye, it becomes cut off from its blood and oxygen supply. This results in sight loss. Symptoms also include dark shadows and blurred vision and should be checked out urgently. Risk increases with age and may be greater if:
Diabetes can cause the tiny blood vessels at the back of your eye to leak, damaging your retina and leading to blurred vision, floaters, flashes and permanent sight loss if untreated.
Sickle cell disease
An inherited condition, sickle cell disease can cause damage to the blood cells in the retina.
This neurological condition, which usually involves severe headaches, can also include flashing lights in your eyes.
Charles Bonnet syndrome
This condition usually affects elderly people with failing eyesight, and can cause flashes and other visual disturbances, particularly in low light.
Although flashes and floaters aren’t usually serious, they can sometimes indicate a sight-threatening problem. It’s important to seek medical advice from your optometrist, GP or local A&E department within 24 hours if:
Your optometrist will carefully examine your retina and may refer you to a specialist eye doctor called an ophthalmologist for further tests and treatment.
However, go to A&E immediately if:
You may not need treatment for flashes and floaters if the cause isn’t serious.
Sometimes flashes will disappear over time and floaters may become less noticeable as your brain adjusts to the changes going on inside your eye.
You can also reduce the impact of floaters by wearing dark glasses when it’s bright.
Otherwise, treatment will depend on the cause. It may include:
 https://www.moorfields.nhs.uk/condition/flashes-and-floaters https://patient.info/health/visual-problems/flashes-floaters-and-haloes  https://patient.info/health/visual-problems/flashes-floaters-and-haloes  https://www.moorfields.nhs.uk/condition/retinal-detachment  https://patient.info/health/diabetes-mellitus-leaflet/diabetic-retinopathy  https://patient.info/health/sickle-cell-disease-sickle-cell-anaemia  https://patient.info/health/visual-problems/flashes-floaters-and-haloes  https://patient.info/health/visual-problems/flashes-floaters-and-haloes  https://www.moorfields.nhs.uk/condition/flashes-and-floaters  https://www.moorfields.nhs.uk/condition/flashes-and-floaters  https://www.moorfields.nhs.uk/sites/default/files/Retinal%20detachment%20surgery_0.pdf  https://www.diabetes.org.uk/guide-to-diabetes/complications/retinopathy/how-is-retinopathy-treated