Flashes and floaters

Floaters are visual perceptions of material contained within a person's eye. Find out what you should do if you have flashing lights and floaters.


What are flashes and floaters?

Floaters are visual perceptions of material contained within a person's eye. The objects seen can appear as spots, nets, flies or cobwebs, which move position or 'float' with eye movement.

Photopsia is the perception of flashing lights. These can take the form of sparks of light, like lighting, or sometimes coloured patterns, swirls, 'zigzags' or kaleidoscope patterns.


There are several different causes for flashing lights and floaters discussed below. But the most common cause of flashing lights and floaters is a posterior vitreous detachment – or collapse of the gel within the back of the eye.

This is a normal process that takes place as we all get older.

What is the vitreous?

The vitreous is a transparent gel-like substance that fills the posterior portion of the eye, occupying approximately four-fifths of the volume of the eye.


The vitreous is also sometimes called the vitreous body, the vitreous gel or the vitreous humour.

It can be thought of as a fairly well structured, firm material in early development, which provides nutrition, as well as acting as a scaffold to support structures of the eye during development.

The vitreous is firmly attached to some of the internal structures of the eye, including the optic disc, the vitreous base and to blood vessels that supply the retina (see figure 1).

Figure 1: Cross section of the eye

Ageing and the vitreous – posterior vitreous detachment?

Posterior vitreous detachment (PVD) is the most common and most important event that occurs in the vitreous.

As a person ages, the vitreous gel slowly becomes more liquefied, losing its firm structure.

During this process, the vitreous attachments to the optic disc (optic nerve head) and retinal blood vessels can break, causing the vitreous to move forward and away from the retina.


This is called a posterior vitreous detachment (see figure 2). As the vitreous detaches from the retina, it can cause both flashing lights and floaters.

In posterior vitreous detachment, flashing lights occur due to the vitreous gel pulling on the retina.

This tugging movement stimulates the retina and the retinal cells 'see' this as flashing lights. Floaters result from condensation of vitreous material within the eye, particularly from the site of attachment to the optic disc.

This produces a large and visible floater – called a Weiss ring. Therefore a posterior vitreous detachment can be thought of as a normal process of ageing, which does not require treatment.

Figure 2: Detachment of the vitreous – posterior vitreous detachment.

How common is a posterior vitreous detachment?

Most individuals will develop posterior vitreous detachment, usually between the ages of 40 and 80 years.

Twenty seven per cent of patients in their 60s and 63 per cent in their 80s have a posterior vitreous detachment.


It may occur at a younger age (less than 40 years old) in patients who are short sighted, have diabetes or who have rare retinal vascular disorders or previous trauma to their eyes.

The fellow eye has evidence of a posterior vitreous detachment in 90 per cent within 3 years.

Can a posterior vitreous detachment cause any harm?

Occasionally during the process of a posterior vitreous detachment, abnormally strong attachments to the retinal blood vessels or to some weak areas of the retina can lead to bleeding inside the eye or the formation of retinal tears or holes.

Although retinal tears or holes occur infrequently, early recognition is important because they often require treatment to prevent a more serious condition called a retinal detachment.


What is a retinal detachment?

The retina is the part of the eye where optical images are formed.

The retina converts light into signals that are sent along the optic nerve to the part of the brain where images are perceived.

The retina of the eye can hence be thought of as the camera film of the eye. When there's a tear in the retina, liquid from the vitreous can get behind the retina and strip it from the underlying choroid.

When this happens, the retina is no longer able to sense and process light signals and therefore the eye effectively stops seeing.

Retinal detachment surgery is required to reattach the retina. The sooner this is done, the better.

How common is a retinal detachment?

Retinal detachment is much less common than a posterior vitreous detachment, with an annual incidence of approximately 12 in 100,000 per year.

However, certain groups of people are more at risk of suffering a retinal detachment.

These include:

  • people that are very short-sighted (high myopes)
  • those who have a family history of retinal detachment
  • those who have had a previous eye injury
  • people who have had previous cataract surgery.

The chance of retinal detachment developing in the fellow eye later on is 12 per cent.

Can a retinal tear be repaired before it becomes a retinal detachment?

A retinal tear can be repaired using a specific form of laser therapy or cryotherapy (freezing treatment), known as retinopexy.

This treatment causes the retina to form a scar, strongly bonding it to the underlying choroid, therefore stopping the retina from detaching.

It's therefore important to detect and repair retinal tears as soon as possible.

Are there causes of flashing lights or floaters other than posterior vitreous detachment, retinal tears and retinal detachments?

Ocular migraine

Migraine is a common cause of flashing lights (photopsia).

Migraines can be associated with visual disturbance (also called an aura) before the onset of headache.

The visual disturbance typically lasts between 10 minutes to an hour, but it's not always followed by a headache.

The photopsia in migraine can be quite variable, ranging from coloured patterns and oil droplet like swirls, to 'zigzags', heat haze, shimmering or kaleidoscope patterns.

Sometimes, there can be temporary black spots in the vision (known as scotomas), which slowly move before resolving.

If you experience symptoms like these for the first time, you should contact your GP or optometrist to confirm the diagnosis.

Age-related macular degeneration

People who have advanced age-related macular degeneration, where the central vision is significantly reduced can occasionally experience flashing lights, due to underlying damage to the photoreceptors of the central part of the retina called the macula.

Vitreous haemorrhage

A burst blood vessel within the eye can result in lots of floaters, which tend to appear black in colour. These can be so profuse that they can cause the vision itself to be reduced.

A vitreous haemorrhage usually is the result of abnormally growing blood vessels, such as those that can develop in people with diabetes, although occasionally a vitreous haemorrhage can occur in association with a retinal tear or detachment.


Inflammation in the vitreous can lead to floaters forming in the eye. This can be self-limiting, but can also be associated with inflammation of other parts of the eye.

It's therefore important to have a full eye examination if there are signs of inflammation inside the eye.

What should I do if I have flashing lights and floaters?

Floaters are very common and they are usually harmless.

However, if you experience new symptoms of flashing lights or floaters, it's important to make an appointment to see an optometrist as soon as possible to exclude an underlying retinal tear or detachment.

Your optometrist will be able to confirm the diagnosis of a posterior vitreous detachment and rule out an associated tear or detachment.

If there is a retinal tear, detachment, or any uncertainty, your optometrist will refer you to an ophthalmology department for a further examination.

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