Researchers from Oxford University say they have made a breakthrough in developing smart glasses for people with severe sight loss.

The devices use a pair of video cameras to enhance residual vision and have the potential to transform the lives of thousands of registered blind people.

The glasses help users to make the most of existing sight and deliver a crucial sense of depth. 

As a result of these features they can prevent users colliding with objects in their path such as lamp posts or tripping over kerbs and steps.

The glasses are being trialled by 30 visually-impaired volunteers at testing venues in Oxford and Cambridge in England, where they will navigate through specially constructed obstacle courses.

At the same time, a handful of users are giving the devices a "real life" airing in public, mingling with shoppers and tourists in the centre of Oxford.

Dr Stephen Hicks, of the Nuffield Department of Clinical Neurosciences at Oxford University, who led development of the glasses, said: "The idea of the smart glasses is to give people with poor vision an aid that boosts their awareness of what's around them - allowing greater freedom, independence and confidence to get about, and a much improved quality of life.

"We eventually want to have a product that will look like a regular pair of glasses and cost no more than a few hundred pounds - about the same as a smart phone."

The device consists of a pair of video cameras mounted in a headset, a pocket-sized computer processor, and software that projects images of close-by objects onto displays in the see-through eye pieces.

The software interprets nearby surroundings to make important objects such as kerbs, tables, chairs or groups of people stand out more clearly.

In some cases, details such as facial features can become easier to see, making social interaction more natural. 

The glasses also work well in low light and can be used to overcome night blindness.

Of the more than 300,000 severely sight impaired people in the UK, it is believed about a third could benefit from the technology.

They include sufferers of sight-loss conditions such as retinitis pigmentosa, diabetic retinopathy, age-related macular degeneration and optic neuropathies.

Many of those affected rely heavily on others to help them get around safely and do simple things such as visiting shops and friends.

Twenty volunteers with a range of eye conditions and levels of vision took part in preliminary tests of an earlier version of the glasses conducted last year by the Oxford team.

Lyn Oliver, 70, from Faringdon in Oxfordshire, who has tried out a number of the scientists' prototypes, said: 'If people are stood outside a shop talking, they often go silent when they see me and watch me walk past. 

"But they've disappeared as far as I am concerned. Have they moved? Have they gone inside the shop? There's a sudden stress about avoiding them.

"The glasses help remove this layer of stress and they do it in a way that is natural to the person using them."

Ms Olvier was diagnosed with retinitis pigmentosa, a progressive eye disease, in her early 20s. 

Most of her residual sight is confined to the edges of the visual field, but she can still spot movement.

She recalled how once last year, when unaccompanied by a guide dog and relying on a cane, she walked into a car.

"With the glasses on, I would have seen the car," she said.

The trials are being conducted with support from the Royal National Institute of Blind People (RNIB).