For up to two billion people around the world wearing glasses for myopia or short-sightedness there may be a surprisingly simple solution on the horizon – eye drops to shrink their larger than normal eyeballs, potentially correcting their vision and in severe cases preventing blindness.
Too good to be true? Not according to a husband-and-wife research team in Melbourne who believe they have established the complex physiological mechanism underlying myopia, revealing a potentially simple treatment to correct it by controlling fluid retention in the eyeball. The researchers – neuroscientists Dr Sheila Crewther and her husband and co-researcher Professor David Crewther – announced recently they have discovered that a diuretic drug, bumetanide, commonly used to control fluids in the treatment of heart and kidney disease, may inhibit the development of short-sightedness. While 'only a first step', the researchers say their findings offer new potential for developing a therapeutic treatment for myopia – the commonest visual disorder, now afflicting more than one in three adults globally.
Visual disorders including myopia are also the fourth most common childhood disability and can have considerable impact on academic achievement resulting in children underperforming at schools across Australia and around the world.
While the increase in shortsightedness among Australian school children has been modest, in Asia, for example in Hong Kong and Taiwan, the prevalence of childhood myopia is up to four times as high. In the UK, about fifty per cent of university students are myopic, says Dr Sheila Crewther. In Singapore up to 80 per cent of young people are myopic by the time they leave school.
Dr Crewther, an Associate Professor of Psychology at La Trobe University's School of Psychological Science, Melanie Murphy a PhD student and Professor David Crewther, Deputy Director of the Brain Sciences Institute at Swinburne University of Technology, published the findings of their latest study online in the journal PloS1 in July.
They believe their discovery may lead not only to prescription eye drops or other simple therapeutic intervention to control myopia – but may also mitigate or prevent the onset of more complicated secondary conditions such as retinal detachment and glaucoma.
The Crewthers' findings are the result of an NHMRC–funded Development Grant to investigate pharmaceutical control of compensatory refractive changes in chickens wearing lenses to alter their visual environment. Their eyes were found to compensate for the power of the lens within a few days so that those wearing 'minifying' (negative) lenses developed myopia (shortsightedness), while those with magnifying (positive) lenses developed 'short eyeballs' and experienced hyperopia or long-sightedness.
The Crewthers say their research revealed that the diuretic drug given during the lens-wearing process only interferes with the induction of myopia, but not hyperopia, indicating a complex interaction between the visual process and fluid movement across a membrane called the retinal pigment epithelium (RPE) surrounding the retina.
The Crewthers have been investigating myopia since the 1980s when they first became interested in the link between visual processing, environmental conditions and myopia.
Myopia requires corrective lenses or surgery to achieve normal vision and in severe cases can even lead to blindness in later life.
Dr Sheila Crewther says it was once believed that most refractive errors of eye were associated with ethnic and genetic differences. Subsequent experimental evidence suggested the cultural environment was equally important – and these latest physiological findings are a highly significant further advance in vision research.
'Increased urbanisation, television, computers and intense education require much greater use of close vision in young people. All have been suggested as potential influences for myopia, but we still don't know the exact cause.
'However, we do know the highest prevalence of myopia is where you have the highest proportion of people living in high-rise apartment blocks and children are under pressure to achieve academically.'
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