Millions of people blinded by conditions such as glaucoma may one day be able to see again after scientists discovered a way to regenerate damaged optic nerves.
Researchers found a therapy called high contrast visual stimulation – making sufferers stare at changing patterns of black lines – helped the nerve cells grow back.
They combined this with gene therapy,which increased the amount of a protein known to promote optic nerve regeneration – and found this triggered an even greater improvement in sight.
Scientists have discovered a way to encourage damaged cells in the optic nerve to grow back, giving hope to millions of people suffering eye conditions such as glaucoma (file photo)
Dr Paul Sieveing, director of the National Institutes of Health’s National Eye Institute, who carried out the study, said: ‘Reconnecting neurons in the visual system is one of the biggest challenges to developing regenerative therapies for blinding eye diseases like glaucoma.
‘This research shows that mammals have a greater capacity for central nervous system regeneration than previously known.’
The optic nerve is the eye’s ‘data cable’, carrying visual information from the light-sensing cells in the retina in the back of the eye, to the brain.
Living near a road could send you to an early grave: Traffic…
‘Give women test that can spare them from breast cancer…
Is dementia in YOUR genes? New test can predict how likely…
Mother left PARALYSED by childbirth and unable to cuddle her…
Like a bundle of wires, it consists of around a million of a type of nerve cells called ganglion.
Each ganglion has an axon – a long, thread-like protrusion extending out of it, along which impulses are conducted from ganglion to ganglion.
A variety of diseases or damage to the optic nerve, such as glaucoma, cause vision loss and blindness when they destroy or damage these axons.
THE COMMON EYE CONDITION THAT CAN CAUSE IRREVERSIBLE BLINDNESS
Glaucoma is a condition which can affect sight, usually due to build up of pressure within the eye.
Glaucoma often affects both eyes, usually to varying degrees. One eye may develop glaucoma quicker than the other.
The eyeball contains a fluid called aqueous humour which is constantly produced by the eye, with any excess drained though tubes.
Glaucoma develops when the fluid cannot drain properly and pressure builds up, known as the intraocular pressure.
This can damage the optic nerve (which connects the eye to the brain) and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).
In England and Wales, it’s estimated more than 500,000 people have glaucoma but many more people may not know they have the condition.
Worldwide, it is the second leading cause of blindness, according to the World Health Organisation.
Glaucoma can be treated with eye drops, laser treatment or surgery. But early diagnosis is important because any damage to the eyes cannot be reversed. Treatment aims to control the condition and minimise future damage.
If left untreated, glaucoma can cause visual impairment. But if it’s diagnosed and treated early enough, further damage to vision can be prevented.
Source: NHS Choices
Glaucoma is caused when fluid cannot drain properly from the eye, and pressure builds, damaging the optic nerve.
In adults, the axons in the cells in the retina fail to regrow on their own, which is why vision loss from diseases of the optic nerve is usually permanent.
As part of the study, researchers took mice and crushed the optic nerve in one of their eyes using forceps.
The rodents were then placed in a chamber several hours a day for three weeks where they viewed high-contrast images – essentially changing patterns of black lines.
Compared to mice that did not receive the high-contrast visual stimulation, the mice that did had ‘significant’ re-growth of the axons in their retinas, researchers said.
Prior work by the scientists showed that increasing activity of protein called mTOR could also promote optic nerve regeneration.
And so they wondered if combining visual stimulation with increased mTOR activity might have an even greater effect.
Two weeks prior to crushing the mice’s optic nerves nerve crush, the scientists used gene therapy to cause the ganglion cells in the retina to overexpress mTOR.
After the optic nerves were crushed, these mice were given high-contrast visual stimulation daily.
After three weeks, the scientists saw more extensive regeneration of their axons – growing around 6mm, they reported
Encouraged by these results, they carried out gene therapy on more mice to overexpress mTOR even more, and ramped up high-contrast visual stimulation by sewing their other working eye shut.
With this approach, axons along the entire optic nerve and into the various visual centres of the brain grew back.
In three weeks, the axons grew as much as 12 millimetres, a rate about 500 times faster than untreated axons.
Lead author Dr Andrew Huberman, associate professor at Stanford University School of Medicine, said: ‘We saw the most remarkable growth when we closed the good eye, forcing the mice to look through the injured eye.
Damage to the optic nerve – which carries information from vision-sensing cells to the brain – can cause irreversible bilndness. But scientists found making sufferers stare at changing patterns of black and white lines encouraged the cells of the optic nerve to grow back, which could restore vision
The animals’s sight was partially restored after they received the treatment, he concluded.
‘This study’s striking finding that activity promotes nerve regrowth holds great promise for therapies aimed at degenerative retinal diseases,’ said Thomas Greenwell, National Eye Institute program director.
Dr Huberman says in future, special filters could be developed, so that people with glaucoma could be given high contrast visual stimulation while playing video games, watching television or while wearing special glasses.
However, he noted that the way the mice’s optic nerves are crushed does not mimic the typical way people are blinded through diseases or injuries.
Next, his team will examine the effects of high contrast visual stimulation in a mouse model of glaucoma.
The research was published online in Nature Neuroscience.