Flashes and floaters

Floaters and flashes are usually nothing to worry about but sometimes they can mean that there is 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, the vitreous humour shrinks, pulling on your retina, the layer at the back of your eye that contains light-sensitive cells. This pulling action sends signals to the nerve that carries visual information from your eyes to your brain (optic nerve), which can cause flashes and floaters to appear. 

Flashes and floaters are usually harmless and are more likely if you're aged 50 or older or are shortsighted.

Other causes of flashes and floaters can include:

• Bleeding into your vitreous humour
• Charles Bonnet syndrome
• Condensation of your vitreous humour causing deposits to form
• Conditions that affect your retina eg diabetic retinopathy and sickle cell disease
• Inflammation of your eye eg uveitis which is inflammation of the middle layer of your eye (uvea)
• Migraines

Flashes and floaters can also be caused by an eye injury or damage to your retina eg retinal detachment or tear.

In rare cases, they can be caused by tumours in your eye.

If you notice floaters in your eye alongside any of the below symptoms, you should seek urgent medical attention: 

• A sudden change in the number, size or shape of your floaters
• Blurry vision
• Eye pain
• Flashes of light
• Loss of vision, including loss of your peripheral vision (side vision)

These additional symptoms, alongside floaters, could mean you have a serious eye condition. 

There are different conditions that can cause flashes and/or floaters. These include:

Posterior vitreous detachment

This is when the vitreous humour inside your eye shrinks and pulls away from your retina. This occurs due to natural age-related changes and is usually harmless. However, it can cause your retina to tear or, if the vitreous humour pulls away suddenly, it can cause a retinal detachment — this can cause permanent vision loss.

Detached retina

A retinal tear can develop into a retinal detachment if it isn’t treated quickly. If your retina detaches from the back of your eye, it becomes cut off from its blood and oxygen supply, which causes permanent vision loss. Symptoms also include dark shadows and blurred vision. If you suspect you have a detached retina, you should seek urgent medical attention. 

Your risk of a detached retina increases with age and may be greater if:

• Detached retinas run in your family
• You’re shortsighted
• You’ve had cataract surgery
• You’ve recently had a severe direct blow to your eye

Diabetic retinopathy

Diabetes can cause the tiny blood vessels at the back of your eye to swell, leak and become blocked — this is called diabetic retinopathy. The resulting loss of a healthy blood supply to your retina triggers your retina to grow new blood vessels; however, these blood vessels do not form properly. Abnormal and damaged blood vessels cause scar tissue to form, which can lead to your retina pulling away from the back of your eye. This can cause permanent vision loss if it isn’t treated urgently. 

Diabetic retinopathy can also increase your risk of cataracts and glaucoma. 

Sickle cell disease

An inherited condition, sickle cell disease produces sickle-shaped red blood cells that can block the tiny blood vessels that supply your retina. This damages your retina, causing vision problems.

Migraine

This neurological condition, which usually involves severe headaches, can also cause you to see flashes of light.

Charles Bonnet syndrome

This condition usually affects elderly people with failing eyesight. It can cause flashes and other visual disturbances, especially in low light conditions, such as hallucinations.

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:

• They appear suddenly or increase in number
• You also have blurred vision
• You also have eye pain
• You’ve recently had eye surgery or an eye injury
• You have a dark shadow moving across your vision
• You lose any vision

Your optometrist will carefully examine your retina. During your eye exam, they may give you eye drops to dilate your pupils so they can better examine your retina. They may also refer you to an ophthalmologist (a doctor specialising in treating eye conditions) for further tests and treatment.

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 effect of floaters by wearing dark glasses when it’s bright.

Otherwise, treatment will depend on the cause. It may include:

• Better management of conditions that are causing problems in your retina, such as diabetes or sickle cell disease
• Laser surgery or medication to treat leaky blood vessels or blockages in your retina
• Surgery to reattach your retina
• Vitrectomy to remove floaters — this surgery is only performed if you have a lot of floaters that are affecting your vision; it involves removing your vitreous humour and replacing it with a fluid that mimics it