For ten years Laura Richardson knew that as darkness fell her vision would change. Her eyes would fill with dancing dots that looked like static on a television screen.

She also found bright light painful. However trips to the optician, GP and an ophthalmologist couldn’t identify any physical problem.

So she learned to manage the symptoms herself, by installing dimmer lights at home that she kept switched low, and wearing tinted glasses — made for her by an optician — which she wore whenever in bright artificial light.

‘I became very depressed and felt that no one truly understood what it was like to see through my eyes,’ says Laura, 30, a counselling student from St Helens in Merseyside.

For ten years Laura Richardson knew that as darkness fell her vision would change. Her eyes would fill with dancing dots that looked like static on a television screen

Then last September she woke up one morning to find that the dancing dots were now appearing in daylight, too.

She could also see ‘after’ images, where for instance, text from a page lingered on her vision.

‘It was a huge shock and I was extremely frightened,’ she says. Her GP sent her back to an ophthalmologist but checks — including an MRI scan — came back clear.

It was not until she did her own research that she found out what was wrong: she suffers from visual snow.

As well as seeing ‘static’, the condition can make those affected sensitive to light, explains Peter Goadsby, a professor of neurology at King’s College London and a leading expert in the problem.

He first came across visual snow when, as a migraine specialist, he was being sent patients whose symptoms were being put down to migraine aura.

But he says visual snow is a different and distinct condition. The cause is unclear but brain scans of those affected have found differences in the visual cortex, the area at the back of the brain that processes visual information.

‘This area is overactive in people with visual snow and it seems to be a disorder of the way in which this part of the brain responds to the information it receives from the eyes,’ says Professor Goadsby.

‘For those affected it can be extremely disabling and affect their work and personal lives.’

Laura Richardson suffers from visual snow. This means that her eyes fill with dancing dots that looked like static on a television screen

As well as the psychological and social impact, the problem has affected Laura in more practical ways — she has to limit use of her phone and laptop, for instance, as these aggravate the symptoms, ‘which has made studying difficult,’ she says.

At the moment there is no cure. Professor Goadsby is working on finding an effective treatment but says people who think they have have the condition should visit their optician or GP to rule out other problems that can cause strange eye symptoms.

But visual snow is not the only eye condition that can make you see things, as the experts explain.

HALLUCINATIONS

People with impaired sight often have hallucinations — seeing things or people that aren’t there.

‘They are caused by the brain responding to the loss of visual input to the eye,’ says Dominic ffytche, a reader in visual psychiatry at King’s College London.

‘The nerves in the visual area of the brain become hyperexcitable, and fire off spontaneously, leading to the hallucinations.’

Many of those affected do not mention it, fearing they have mental health problems (or dementia) but the phenomenon is a recognised medical condition called Charles Bonnet syndrome.

People with impaired sight often have hallucinations — seeing things or people that aren’t there. They are caused by the brain responding to the loss of visual input to the eye

It affects about 10 per cent of people with moderately impaired eyesight, perhaps due to cataracts (where the lens becomes cloudy) and glaucoma (when pressure builds up in the eye damaging the optic nerve), although in fact anyone who can’t see from about halfway down a standard eye test letter chart can develop it.

The hallucinations will range from coloured blobs and patterns to faces, figures and animals. About 20 per cent of patient with Charles Bonnet see people in elaborate costume.

‘The hallucinations are not memories of visual experiences stored in the brain, so the faces or figures are not familiar and they have no direct relevance to the person experiencing them,’ explains Dr ffytche.

The hallucinations generally develop within weeks of the vision loss, and generally reduce over the following 18 months as the brain adapts to the loss of sight.

Altering the light levels either up or down, or a series of specific eye movements can help, it is thought, by activating the under used visual parts of the brain that cause the hallucinations.

Some medications for epilepsy, dementia and psychosis can reduce hallucinations by dampening over activity in the nerves of the brain, but carry the risk of significant side -effects.

Hallucinations due to Charles Bonnet syndrome will range from coloured blobs and patterns to faces, figures and animals

Other conditions can cause visual hallucinations such as dementia and Parkinsons’s disease.

In this case it is thought to be due to a lack of the brain chemical acetylcholine, which plays a role in visual processing and here the hallucinations tend to be figures and animals that are more likely to be familiar than those that occur in Charles Bonnet syndrome.

‘Anyone with hallucinations should go and see their GP, although knowledge of the syndrome can be limited so it can be worth taking along a leaflet about it to the appointment,’ says Dr ffytche.

FLOATERS AND FLASHES OF LIGHT

Many people have floaters, dots or lines that trail across their vision. These are caused by strands of collagen in the vitreous, the jelly-like substance that fills the eyeball.

This collagen can deteriorate naturally with age and bits break off and float across the line of vision.

But a sudden influx of new floaters in the vision, especially if accompanied by flashes of light can be a sign of posterior vitreous detachment (PVD).

This occurs when the gel in the eye becomes more watery, normally as a result of ageing; the gel shrinks and tugs at the retina, the thin layer of light sensitive cells at the back of the eye which send visual information to the brain.

Many people have floaters, dots or lines that trail across their vision. These are caused by strands of collagen in the vitreous

As the gel tugs at the retina it can release floaters, and stimulates the light sensitive cells, hence flashes of light appear in the vision.

Floaters can also be a sign that the retina has torn or pulled away from the back of the eye, which without prompt treatment can lead to a partial or total loss of sight.

‘The flashing lights in PVD are generally seen in dim light whilst in a retinal tear or detachment, they are brighter and can generally be seen in normal light,’ says Professor Stephen Vernon, a consultant ophthalmologist at University Hospital Nottingham.

A patient can’t reliably detect between the two so should see an optometrist or visit an eye A&E, ideally within 24 hours of the symptoms starting.

Retinal tears can be treated with a laser as an outpatient, whereas a retinal detachment will require an operation to reattach the retina.

HALOS

Seeing halos around lights can be a sign cataracts are developing. They occur when the usually clear cells of the lens become cloudy, due to changes in the consistency and volume of the proteins in them.

This alters the way light travels through the lens so that lights can appear to have halos.

Professor Vernon explains that halos can be an early symptom of cataracts.

‘Cataracts are more common in people over 60, particularly if the patient has diabetes,’ he says.

Seeing halos around lights can be a sign cataracts are developing. They occur when the usually clear cells of the lens become cloudy

‘They can also be brought on by certain medications, in particular steroids when taken by mouth or when used in eye drops for extended periods.’

Cataracts are treated by surgically removing the cloudy lens and replacing it with a plastic one.

ZIG-ZAG LINES

A jagged zig-zag line travelling across vision is a classic symptom of migraine aura. Aura are the neurological symptoms that some people experience in the run up to a migraine.

The aura symptoms usually last for up to an hour, and occur in about 30 per cent of the eight million people in the UK who have migraine. Some get aura symptoms without the throbbing head pain – a condition known as silent migraine.

Migraines begin with a wave of electrical energy that travels slowly over the surface of the brain, and this is believed to cause the aura symptoms.

‘They commonly last between five and 60 minutes,’ says Dr Andrew Dowson, a migraine specialist at the east Kent Headache Service.

A jagged zig-zag line travelling across vision is a classic symptom of migraine aura. Aura are the neurological symptoms that some people experience in the run up to a migraine

The most common symptoms include seeing a zig-zag line that moves slowly across the field of sight. Other possible visual signs include flashing lights and sparkles.

‘The mainstay of treatment is prevention,’ says Dr Dowson. He recommends daily supplements of magnesium (200-600mg) and vitamin B2 (100mg). That’s because a deficiency of magnesium may contribute to the wave of brain activity that triggers aura symptoms.

Dr Dowson says 75mg of aspirin daily also can help reduce the symptoms of aura by changing the way that the brain uses the chemical serotonin — serotonin appears to have a key role in both pain and aura in migraine, it’s thought by influencing the way blood vessels behave.

However, check with your doctor as long-term, aspirin carries the risk of gastric bleeding.

PS: Despite what you see in the cartoons people who have hit their head rarely see stars or flashing light says Colin Shieff, a retired consultant neurosurgeon who is now trustee of Headway, the brain injury association.

They are more likely to have double vision or temporary sight loss, he says.