Flashes and floaters are common symptoms which often affect normal eyes. They usually occur because of changes that happen in the jelly-like substance inside the eye (the vitreous humour). The most common causes need no treatment and tend to settle by themselves. However, flashes and floaters can occasionally be warning symptoms of retinal detachment.
Haloes are bright circles which seem to surround a source of light. They are also referred to as glare. They are common, particularly in older people. They can be unpleasant and uncomfortable and lead to temporary dazzling which may particularly affect driving at night. They can sometimes be a sign of underlying eye conditions like glaucoma.
What are flashes?
Experiencing flashes in the eye, often at the edges of vision, is fairly common. Each flash, which can vary from a bright light to almost a sparkle, lasts a varying length of time. Periods of flashing can go on for several months. The symptoms are often most noticeable when going from a light to a dark room.
What causes flashes?
Flashes are most commonly due to changes in the vitreous humour. The vitreous humour is the jelly-like substance which fills the inside of the eye, between the lens and the retina. The vitreous humour is contained in a fine membrane and this is attached to the retina at the back and the lens at the front.
As we age, the vitreous humour shrinks and as it does so it can pull on the retina. This can cause flashes as the pulling sends signals to the seeing nerve (optic nerve). Eventually the vitreous tends to pull right off the retina, a condition called posterior vitreous detachment. This condition is harmless in itself and happens to most people as they age. The vitreous is detached from the retina in 75% of people over 65 and this is usually harmless. Sometimes, however, as the vitreous pulls on the retina it can tear it, causing a retinal tear or retinal detachment.
Some people with migraine experience flashing lights in the eye. Usually, in migraine, these occur in both eyes at the same time. They can last up to an hour and tend to increase to a maximum before fading away and being replaced by a headache.
Charles Bonnet syndrome is a condition experienced by people, usually elderly people, whose vision is deteriorating. The brain, deprived of real visual information, can make things up instead, particularly in conditions of low light. Patients may sometimes see flashes but more frequently they see complex visual images like children or animals, which can look very real.
Can flashes be serious?
Most flashes are caused by changes in the vitreous humour which are related to age and which are harmless. Occasionally, however, flashes can be a sign that the retina is at risk of being torn or detached. Increasing, persistent or constant flashes all suggest strong pulling on the retina and may mean that you are at risk of retinal damage. Flashes accompanied by a shadow coming down over your vision is suggestive of retinal detachment.
What are floaters?
Floaters are shapes (opacities) floating in the field of vision. They may look like spots, threads, spiders or cobwebs. They move as you move your eye and can seem to dart away when you try to look at them. They drift about inside the eye rather than staying still. They tend to be more obvious when bright objects, such as a blue sky, are being viewed.
Most floaters are also caused by changes in the vitreous humour. Most commonly this is due to normal ageing of the eye, when opacities form in the clear jelly and drift around. These kinds of floater are not associated with flashes or reduction in your vision and they tend to come on gradually. They also tend to 'settle' at the bottom of the eye, below the line of sight. After a while you will find them less noticeable. They are more common in those who are short-sighted, those who have had eye surgery and those who have diabetic eye disease.
Floaters can also occur after posterior vitreous detachment. In this case there will be a sudden obvious increase in the number of floaters. Flashes may also occur. Again, there should be no loss of vision and most cases settle without causing any problems.
Bleeding into the vitreous humour (vitreous haemorrhage) will also lead to the formation of floaters. However, in this case the floaters represent blood in the jelly. If the bleeding is major then vision may be affected. For more information on this condition see separate leaflet called Vitreous Haemorrhage.
Floaters will result from any internal damage to the back of the eye. Retinal tears and retinal detachments will also cause floaters and these will vary with severity depending on the severity of the damage.
Less common causes of floaters include inflammation of the eye (posterior uveitis) and, more rarely still, tumours affecting the eye.
Are floaters serious?
Floaters are usually not serious. However, you should see your doctor or optician if:
- They come on suddenly.
- There are large quantities of them.
- They are particularly disturbing.
- They are associated with other eye symptoms such as pain, changes in your vision, grey shadows in your vision or with new onset of flashes.
What are haloes?
Haloes are rainbow-like coloured rings around lights or bright objects. They usually occur because there is extra water in the layers of the eye. The most common and important cause of this is acute glaucoma. If you have glaucoma, you have increased pressure in your eye. This is a very painful condition which can threaten your sight if not treated promptly. However, another cause is chronic glaucoma comes on more quietly and is not painful.
Many other conditions can cause you to experience haloes. These include watering or tearful eyes, overuse of contact lenses, cataracts and opacities in the vitreous humour. Some prescribed medicines may also cause you to see haloes, including digoxin and chloroquine.
Are haloes serious?
Because haloes can be a sign of increased pressure in your eye (glaucoma) then it is important you see your doctor or optician if you develop persistent haloes. It is also important that you do not drive in conditions where haloes may be affecting your vision - for example, when driving at night. If you have any doubts about your fitness to drive it is your responsibility to speak to the DVLA, who will advise you.
Who develops flashes, floaters and haloes?
Most people will notice occasional floaters, as there are often small opacities and crystals in the vitreous. Because more marked floaters, together with flashes and haloes, are mostly caused by conditions occurring naturally in older eyes, most people who experience them are older. This usually means over 60 years of age, although occasional floaters are not uncommon in people in their 40s and 50s.
Children and young adults may also experience flashes, floaters and haloes, particularly if there has been trauma or surgery to the eye or if they have other existing eye disease. These might include inflammatory conditions of the eye like uveitis, and conditions which can affect the retina like sickle cell disease and the form of retinopathy that can affect very premature babies.
When should I worry about flashes, floaters or haloes?
You should seek advice about floaters and flashes if they are very marked or sudden in onset. You should also seek advice if they are associated with pain, changes in your vision, of if both floaters and flashes are occurring together. You should always seek advice if you develop persistent haloes.
Your first port of call, depending on the severity and timing of your symptoms, may be your optician, GP surgery or accident and emergency department. Most opticians are able to check the pressures in your eyes in order to rule out glaucoma. Many will have equipment to allow them to fully examine the back of your eye for signs of damage to the retina.
Dr Mary Lowth
Dr Mary Lowth
Dr Hayley Willacy