Carol is making up for lost time. At 24, she's going back to college to gain NVQs, brushing up on her numeracy and literacy. Affected by cerebral palsy and with mild cognitive impairment since childhood, she's also got tunnel vision caused by the eye condition glaucoma.

But that hasn't stopped her considering some more exotic courses. "I want to do horticulture and survival cookery," she says. "I like to challenge my eyesight."

But until she was 18, her sight loss was undiagnosed. "I was cited in a medical journal," she says. "I was so young to have it. The consultant thought I had probably had it from a young age."

Carol has always worn glasses, but had huge problems at school. "I was always moved closer to the board. But before I'd copied anything down it would be wiped off. They assumed there was a problem with my glasses."

In fact, Carol can only see colour out of one eye and has tunnel vision so bad it is like looking through the hole in a needle, she says.

"I thought everyone saw the way I did. School and college were my downfall really. That's why I am going back to college now."

Carol has glasses designed for her sight loss and takes drugs to prevent the glaucoma worsening, but she has no real idea how long it deteriorated before she was diagnosed.

Worryingly, Carol is not alone. According to NHS figures 30% of people with a learning disability have a diagnosed visual impairment.

But astonishingly, a further 50% of people with learning disabilities have undiagnosed sight problems, according to the RNIB, and may be losing their sight unnecessarily.

The charity is now seeing results from an initiative launched with NHS Ayrshire and Arran in 2003 to address the problem.

The Bridge to Vision programme has brought together local optometrists with NHS staff and the RNIB's own support workers to offer proper eye checks to hundreds of people with learning disabilities. Already 250 people in Ayrshire and Arran have been tested.

According to Ayr optometrist Peter Carson, there are a number of reasons why eye problems aren't picked up in many cases, including faulty assumptions and discrimination, but also simply because it can be difficult to test vision, particularly if a learning disability is severe.

Carers and eye specialists alike may assume that behavioural problems such as rocking, being withdrawn or uncommunicative, making unusual noises or lashing out are to do with someone's disability. In fact, they may be down to a sight problem which no one is even looking for.

"A lot of people are not being brought along for regular eye checks, perhaps because it is a assumed they wouldn't necessarily benefit," Carson says. "Younger people with learning disabilities and visual impairment tend to get picked up, maybe in hospital or specialist schools. But it is when they get further down the line into adulthood that the problems arise.

"We see people in their 40s being brought along with cataracts, and you don't know - was that congenital, or has it developed in their 40s? There's no history so you can't tell."

The irony is that people with learning disabilities are more prone to sight loss. A number of conditions leave those affected more likely to have particular vision problems. Downs syndrome, Usher's syndrome, fragile X and cerebral palsy are all recognised as being linked to eye conditions.

The idea of being blind or near blind and your condition unknown to your carers is a frightening one and the RNIB's Eleanor Ogilvie has some horror stories - one woman the charity came across had lost her eyesight and her carers had no idea how it had happened or when. The RNIB has come across elderly people with learning disabilities who have never been able to see. "One woman's problems had been attributed to learning disability and she had spent 80 years of her life in total isolation,"

Ogilvie says.

Worsening eyesight is another problem. In the past, people with many learning disabilities were not expected to live as long as they now do, and eyesight can deteriorate. "Parents and carers won't necessarily be aware of the importance of having their sight tested," Carson says.

But testing them can be problematic for High Street optometrists too. It may be impossible to use traditional sight charts which depend on letter recognition. Behaviour problems or anxiety may make consultations difficult.

Entering a darkened room to let a stranger shine a light in your eyes is too stressful for some people. "Some people cling to the doorposts to avoid coming in," Ogilvie says.

In Ayrshire and Arran, RNIB-trained project assessment workers (PAWs) will meet with someone scheduled for a test to do an initial assessment and prepare them. A report is also readied for the optometrist, suggesting a tentative diagnosis and ways of calming the patient's anxieties.

The PAWs worker will usually accompany them to the appointment, and comforting toys or sweets which might make the experience easier will be planned ahead. "It can be enough to allow people a bit more time to sit in the chair, examine the torches. Or it may help to let the optometrist know - this person prefers males, or females, or if you approach them from the left you may get a right hook."

The programme offers training to optometrists and a fund for the purchase of basic equipment - such as Cardiff cards, which allow the sight to be tested with large pictures of varying faintness. The preferential looking test is effective even if people have fairly severe disabilities.

"Even if there is no communication it can work," says Carson. "But if that doesn't work you can make an assessment with something as basic as waving your tie. In the worst case scenario you can only shine a light in to see if the eyes react."

The training is helpful, he says. "It is covered during optometrists' university-based trainingwhich syndromes come with classic eyesight presentations. But if you have a patient sitting in front of you on a chair you are not necessarily going to make the connections."

Carson estimates the average high street optometrist might see six to 12 clients a year with a learning disability. "That means you are not going to get a high level of expertise on one specific learning disability. Some people across Scotland may have developed a bit of skill due to working near where some people with learning diabilities live - such as a centre for people with autism. But you often have to think on your feet, how do I do this?"

In general, clients under Bridge to Vision will get a double length appointment, giving more time for assessment. The pre-visit reports are also valuable, he says. "What was a challenging visit before is now much more straightforward."

Now the RNIB is pushing to have the same system offered elsewhere in Scotland and the rest of the UK. More than 200 people are PAWs trained across Scotland, but none have the co-ordination which makes the Ayrshire and Arran scheme so effective, Ogivlie says.

"It was driven by the health board, but optometrists, the health board and the RNIB were all on board right form the start. Other projects don't have that and funding can be difficult because it's so multi-disciplinary."

However, the funding needed isn't huge. Bridge to Vision costs around £30-40k a year, and could be using existing money better. "Without it we could be spending money on behaviour modification for some people which could be kept to address their sight problem," Ogilvie says.

"There is not a lot of extra work needed, just a wee bit of care and attention."

Carol makes the same plea. "I think people make too many assumptions. If people showed a bit more patience, disabled people would have a better chance of enjoying their live.

"I used to go to the optician and I assumed if there was anything wrong they would tell me."

She's not bitter, though. "Everybody is learning all the time, I don't blame anybody," she says. Carol has asked us not to use her full name.

Putting eyesight to the test There are about 1.5m people with learning disabilities in the UK. Around 80% of people with learning disability have some form of visual impairment. People with learning disability are up to 200 times more likely to have a sight problem. Sight loss in people with learning disability usually remains undetected. As many as 50% of people with learning disability cannot recognise the alphabet - hampering traditional eye tests. RNIB believes visual impairment, not diminished capabilities, is responsible for holding back many with learning disabilities.