Scientists have discovered strands of genetic code linked to short sight, the most common eye disorder in the world.
The findings shed light on what goes awry to make distant objects look blurred, and raises the prospect of developing drugs to prevent the condition.
Understanding the biological glitches behind short-sightedness could help researchers develop eye drops or tablets that could be given to children to stop their vision from failing as they get older.
Short-sightedness, or myopia, usually starts to manifest early on in life.
The extent to which genes are to blame varies, but for those with the worst vision, around 80% of the condition is caused by genetic factors.
Two separate studies, published in Nature Genetics journal, found variations in DNA that were more common in people with short sight. Chris Hammond, at King’s College, London, found one section of DNA on chromosome 15 was more common in people with myopia. Caroline Klaver, at Erasmus Medical Centre in Rotterdam, found another strand, also on chromosome 15, linked to short sight.
Myopia
The variations in DNA amount to misspellings in the genetic code. These alter the activity of three genes that control the growth of the eyeball and ensure light entering the eye is converted into electrical pulses inthe retina.
To find the gene, the first to be linked to short-sightedness, or myopia, the researchers compared the DNA of more than 4,000 British twins. Twins are often used in such studies because it is easier distinguish the different effects of nature and nurture.
They then confirmed their results by studying the genetics of another 13,000 British, Dutch and Australian individuals.
Some 45 per cent of Britons have the rogue gene and those who have two copies of it are almost twice as likely to be short-sighted as those who are free of it.
The gene, known as RASGRF1, is thought to play a key role in the development of the eye and the passing of visual signals to the brain for processing. When it is faulty, the eyeball may overgrow, making distant objects seem fuzzy or blurred.
Dr Chris Hammond, also of KCL, said: ‘Myopia, or shortsightedness, is the most common eye problem, affecting over a third of adults in the UK.
‘People who are extremely short-sighted carry significant risks of future vision loss. The retina can peel away from the back of the eye like wallpaper off a wall.
‘While we believe that environmental risk factors such as a lot of close work and lack of outdoor activity are implicated, we have not previously understood how people become short-sighted.
‘We hope that by understanding the mechanisms we can stop children from becoming shortsighted and stop short-sighted children from becoming more short-sighted.’
Myopia (Greek: ??????, mu?pia, “nearsightedness”), is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed.
For those with myopia Visual perception, far away objects appear blurred and near objects appear clearly. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or “farsightedness” or “long-sightedness”—this is where the cornea is too flat or the eye is too small.
Eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, but this does have many risks and side effects. The corrective lenses have a negative optical power (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.
Alternative ideas and methods of treatment exist, most notably the claim that myopia is caused by excessive near sight work.
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A miracle eye implant has restored sight to the blind, said the Daily Express. Many newspapers reported this ‘proof of concept’ trial in three patients who were completely blind due to a genetic condition. Each patient had a microchip implanted into one of their eyes, which was designed to convert light patterns into electrical impulses that could be fed into the optic nerve.
All three patients were better able to perceive light and locate light objects on a dark table. Furthermore, one patient could recognise objects such as a cup and a spoon on a table and could determine letters.
As the Daily Express implies, this is exciting research. Although complete vision restoration remains a long way off, a crude improvement in vision from complete blindness is a promising result. As this was a small pilot study, further work is needed to assess how well the device works in a larger group of patients and to refine the surgical technique and the device itself.
Where did the story come from?
The study was carried out by researchers from The University of Tübingen and other institutes and organisations in Germany and Hungary. The device is produced by Retina Implant AG, Reutlingen, Germany. The trial was funded by the German Federal Ministry of Education and Research. The study was published in the (peer-reviewed) medical journal, Proceedings of the Royal Society B (Biological sciences).
The research was explained well by the newspapers, most of which sensibly mentioned that this is preliminary research in three patients with a particular subtype of blindness and that the vision or light perception gained was modest and not complete.
What kind of research was this?
This clinical pilot study tested whether an experimental device can restore vision in blind adults with a particular form of inherited blindness. The electronic chip that is implanted into the eye is positioned on the damaged retina so that light that enters naturally through the eye’s lens hits the chip. The chip is designed to convert this light into a series of electrical impulses that are picked up by the remaining, undamaged cells in the retina. In theory, these impulses would replace the part of the process of vision that had been damaged by the illness.
The researchers assessed whether the visual function of three blind participants, such as discerning between light and dark and patterns, improved after receiving the implant.
What did the research involve?
The chip had 1,500 individual light-sensitive elements. These were designed to pass on electrical impulses to the nerve cells in the eye. The impulses varied depending on the pattern and intensity of the light that hit the chip.
The study was in two men and a woman aged between 38 and 44 years. All of the patients had hereditary retinal degeneration, but had had good vision prior to losing their site. They had all lost their reading ability at least five years before the study and now only had the ability to perceive light but not to recognise shapes.
The device was surgically implanted into the eye under the retina. A week later, the patients were given a series of tests of their visual ability to see if they could perceive light, detect movement, and differentiate between different light sources. Tests involved different light stimuli and included being required to identify the direction of some lines (horizontal, vertical of diagonal) and identifying letters and shapes.
What were the basic results?
All three patients were able to perceive light from the chip. Patient two was able to report the direction of the grid lines indicating an improved resolution of light. In the letter recognition task, Patient two was also the only one able to reliably distinguish between different letters, including the letters L, I, T and Z on a screen when the letters were 8.5cm high from a distance of 63cm away. This patient could also differentiate between different shapes and could differentiate seven out of nine contrast differences in a range of grey cards that varied in shade by 15% darkness increments.
In a more natural task, the patients were asked to identify white objects on a black table in front of them. Patient one reliably located a saucer, a square and a cup on the table. Patient three could locate and differentiate a large plate from a saucer. Patient two could locate and correctly describe a spoon, a knife, a cup, a banana and an apple.
The researchers reported that all three of the patients showed distinct learning effects, but that these could not be quantified in this first pilot study.
How did the researchers interpret the results?
The researchers said their study demonstrated that “subretinal micro-electrode arrays can restore visual percepts in patients blind from hereditary retinal degenerations to such an extent that localisation and recognition of objects can provide useful vision, up to reading letters”.
They admit there are still biological and technological obstacles to be overcome and described approaches taken by other groups to develop this sort of device. They said their device had the advantage that all of its parts could be implanted invisibly into the body and could connect with the processing systems of the retina to provide a continuous, stable image.
They say that this study is proof of concept that electronic subretinal devices can potentially improve visual function from a state of complete blindness to one of low vision, thereby allowing localisation and recognition of objects up to reading capability. They say that further development is needed to improve the contrast and spatial resolution that users experience.
Conclusion
This is a proof-of-concept study designed to investigate whether a device of this type could be used to restore any visual function in patients with heredity blindness caused by degeneration of the retina. The research has shown promising results and this was particularly the case in one of the three patients.
The researchers highlight that the patient who had the most successful response was the only one to have had the chip placed under a part of the eye called the macula, the area usually involved in fine central vision. Following this study, further research is needed to optimise the implantation surgery procedure for this device.
Larger studies are now needed to assess how effective this device is and how it can be further improved. The BBC reported that the team are now testing a more compact upgrade to the device, which can be placed entirely under the skin and powered through a socket implanted behind the ear.
A new study is examining the use of photoscreening to detect amblyopia, or ‘lazy eye’ in children aged 6 months to 6 years.
Amblyopia, known as “lazy eye,” is a major cause of vision problems in children and a common cause of blindness in people aged 20 to 70 in developed countries.
Experts at University of Iowa used the Medical Technology, Inc. (MTI) PhotoScreener, which records the pattern of light reflected through each of the child’s pupils as the child’s eyes are photographed.
Photoscreened images were then assessed by a trained reader and children with abnormal results were referred to ophthalmologists or optometrists for thorough eye exams.
About 4 percent of children screened needed follow-up for possible amblyopia, which corresponds to the expected rate of the disorder in the general population.
“This program has had a lasting, beneficial impact on the children of Iowa, and seems to be cost-effective as well,” medical director William E. Scott, of the University of Iowa said.
Amblyopia is usually treated with special eyeglasses, patching of the stronger eye, medications, or a combination of approaches.
The study is published in October’s Ophthalmology journal.
Scientists have identified a gene that causes short-sightedness, a discovery which paves the way for treatment to prevent one of the world’s most common eye disorders. So could this mean the end of spectacles?
A pair of glasses used to come with its own brand of humiliation in the classroom.
“Four-eyes”, “Specky-git” and “Goggles” were some of the names that rang out in the playground and scarred many a childhood.
Short-sightedness, or myopia, which makes distant objects appear blurred, often begins in childhood, and it appears to be growing in the UK – now affecting about one in three British adults. But a scientific breakthrough announced this week could start to reduce that number within a decade.
Scientists based in London have identified a gene that causes myopia and are confident that drugs could be developed to halt the distorted growth of the eye that brings about the condition. In about 10 years, shortsightedness could be cured through eye drops, says Dr Chris Hammond, who led the research at King’s College London.
“We’ve known for many years that the most important risk factor to short-sightedness as you get older is family history,” he says.
“If one parent is shortsighted then you have a significantly increased risk of being shortsighted, and if you have two shortsighted parents, then you have an even greater risk. But until now, we hadn’t identified any genes responsible for that susceptibility.”
In a 12-year study which looked at 4,000 twins, the researchers at KCL’s Department of Twin Research identified the RASGRF1 gene as one which had variations shared by people with myopia. A separate study in the Netherlands has found a second gene which also governs short sight, and Dr Hammond believes multiple genes are probably responsible.
http://www.bbc.co.uk/news/magazine-11285011