How a laser could prevent age-related blindness

By Pat Hagan
PUBLISHED:21:18 GMT, 29 April 2013| UPDATED:06:40 GMT, 30 April 2013

 

 

A laser that destroys harmful deposits in the eye in a fraction of a second may help to prevent age-related blindness.
The laser works by firing pulses that take only three nanoseconds — three billionths of a second — to hit their target at the back of the eye.
These destroy deposits that can lead to age-related macular degeneration (AMD), the UK’s leading cause of blindness and a condition that affects around 600,000 people. With Britain’s ageing population, the numbers left blind by it are set to rise.

The laser works by firing pulses that take only three nanoseconds - three billionths of a second - to hit their target at the back of the eye

The laser therapy — so fast patients are in and out within ten minutes — could be the first treatment that stops the condition in the early stages, preventing blindness.
AMD usually develops after the age of 50 and is caused by the growth of new blood vessels over the macula, an oval-shaped area at the back of the eye that helps us pick out visual details clearly.
These blood vessels leak fluid, causing scar tissue to form and destroy vision in the centre of the eye, making it difficult to recognise faces, read or watch TV.

 

Around 90 per cent of cases are ‘dry’ AMD, which comes on slowly over several years and for which there is no treatment.
The rest involve wet AMD, which can cause blindness in as little as three months. Treatment involves monthly injections into the back of the eye with drugs designed to curb the growth of abnormal blood vessels. Administered early, it can prevent complete loss of vision but cannot reverse the disease.
But scientists hope the new laser therapy will be able to halt both forms of AMD in their tracks before any vision is lost. This is because before abnormal blood vessels start to grow, yellow-white deposits called drusen often form at the back of the eye. These are made up of lipids, a type of fat, and accumulate when the ageing eye becomes less efficient at disposing of waste from cells that have died off naturally.
Small, widely scattered deposits are not normally a problem. But large ones that are closer together can trigger the process that leads to the growth of abnormal blood vessels because new vessels form to bypass the harmful deposits.
Previous laser therapies have had limited success and can cause collateral damage to the surrounding healthy eye tissue — despite lasting a few hundredths of a second, their pulses still generate enough heat to harm healthy areas.
But the nanosecond laser, the Ellex 2RT, is so fast and accurate it appears to leave this tissue unscathed.
Usually, the patient needs only 12 pulses per eye, so total treatment time is less than half a second.

Previous laser therapies have had limited success and can cause collateral damage to the surrounding healthy eye tissue

In a small trial involving 24 patients in AMD’s early stages, the laser treatment led to an improvement in central vision in 64 per cent of volunteers after 12 months. Most also saw a significant reduction in the fatty deposits and, crucially, scans showed no damage to delicate photoreceptor cells nearby.
Professor Robyn Guymer, who led the study at the Centre for Eye Research Australia in Melbourne, said: ‘Patients reported that the treatment was completely painless. By getting rid of the fatty deposits, we hope to reverse the degenerative processes caused by the disease.’
Dr Sobha Sivaprasad, consultant ophthalmologist at King’s College Hospital in London, said the therapy might prove helpful if larger-scale trials show it actually reduces the incidence of AMD.
But she stressed that fatty deposits in the eye are thought to be only one of several risk factors for AMD. Others include obesity, heart disease and family history.
Manwhile, patients with age-related macular degeneration are being given a dose of the impotence drug Viagra in a clinical trial at Duke University in the U.S.
It is thought to boost the choroid, the layer of tissue that covers the retina (the light-sensitive tissue at the back of the eye).
With age, the choroid can become thinner, leading to the formation of drusen.
One theory is that thinning of the choroid is involved in the development of AMD — so thickening it could potentially slow down the course of the disease.
Earlier studies have shown that a single dose of sildenafil citrate, or Viagra, appears to thicken the choroid in young healthy patients.


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