By Amanda Hargreaves
Producer, BBC Radio Scotland's Investigation
One-in-five people in Scotland is suffering from the effects of a debilitating eye condition very few experts are aware of or trained to deal with.
The Investigation's Shelley Jofre being tested for binocular instability
You can't read without getting a headache from trying to focus on the print, which seems to dance and blur before your eyes.
Or you're not able to meet someone's eyes, because you're seeing two faces and four eyes.
That's the situation for 20% of Scots today and it's the subject of the latest Investigation from BBC Radio Scotland.
These people suffer from a condition called binocular instability, but most of them don't know it.
It takes the form of a turf war between the left and right eye over a tiny fraction of a millimetre difference in focus.
The result is delayed processing of information at the most basic level.
This means the brain has to work incredibly hard to make sense of what the eyes are seeing.
The result is that everyone thinks you're developmentally subnormal.
It's a condition that ruins lives and yet there's a simple cure.
In this month's The Investigation, Shelley Jofre reveals the devastating impact the condition can have on the lives of one-in-five Scots, and why there's so little awareness of it.
"If you can't process visual information, there's not much going for you to be honest," says mum Debbie Ratley.
Charlotte Alguero said it took perseverance to get a diagnosis
Her 12-year-old son Lewis suffers from binocular instability as well as another vision problem dubbed visual stress, or Mears-Irlen Syndrome.
Both problems often co-exist and have very similar symptoms.
Fellow sufferer Charlotte Alguero, now a student at Glasgow School of Art, recalls visiting optician after optician and having no luck anywhere.
"It was a real nightmare," she says, until she was finally diagnosed with binocular instability and visual stress.
"It's like sitting in the back of a car and the world strobes past you through the window. It can be really nauseating."
Yet the condition isn't easily spotted in a routine eye test.
You could easily have 20/20 vision and still have binocular instability.
So diagnosis is a big part of the problem - Nadia Northway, who runs the Visual Stress Clinic at Glasgow Caledonian University explains that you need to be a trained orthoptist to spot the condition.
WHAT TO LOOK OUT FOR
If your child is having difficulties at school, check if the following apply:
They complain of tiredness or headaches after reading
They complain of the print becoming blurry
They find it easier to read on a coloured background
They rub their eyes after reading for a while
They often lose their place when reading aloud
They often misread short words
But there is no longer a training facility for orthoptists in Scotland.
These specialists are "tucked away in eye departments in hospitals where the general public can't access them very easily".
According to research Nadia has been carrying out on adults with literacy problems, as many as 80% of people who have difficulty reading appear to have a problem with binocular instability and/or visual stress.
Once spotted, both problems need different treatments - exercises and corrective glasses for binocular instability and coloured lenses for visual stress.
The condition also runs in families, so if your problem isn't spotted, you and others in your family could spend years battling against this hidden disability without knowing what the problem is.
After all, how would a five-year-old child know how reading should feel?
He/she would probably just assume that everybody found it tiring and painful.
According to psychologist Dr Anna McGee such children grow into under-achieving adults at best, or develop behavioural problems and get into a cycle of disruptive behaviour which escalates as they get older.
It's easy to see how lives are ruined by this problem.
During the course of the programme, Shelley underwent an eye test and discovered that she herself has visual stress, and that she's in need of coloured lenses.
She found that print words stopped blurring and moving when she looked at it through a purple coloured overlay.
Her problem is a mild one, but for anyone more severely affected, experts advise regular eye tests (they're free now on the NHS) - at least once every two years if you're symptom free.
Children should have their eyes tested once a year, as their sight changes all the time.
If you suspect that you've a problem even though you're already wearing glasses, or even if you're given the all clear in a routine eye test, ask your GP to refer you to the orthoptics department of your local hospital where you can be properly assessed and given treatment if necessary.
The Investigation was broadcast on BBC Radio Scotland at 0850 BST on Monday, 4 June.