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Amblyopia, or lazy eye, affects two to four per cent of all children. It is the most frequent reason for children being referred to an ophthalmologist in the UK. The condition means that one eye has deteriorated in its ability to see detail because it is suffers some disadvantage to the other eye. The most common cause of disadvantage is strabismus (crossed eyes) but other conditions such as congenital cataracts can also cause amblyopia.
The condition can be treated in young children of up to about eight years by such measures as the wearing of eye patches. However, in older children and adults, as the brain increasingly prefers images from one eye, the condition is not curable. This ultimately leads to extremely poor vision or even clinical blindness in one eye for the sufferer. The condition affects binocular vision and depth perception, harming quality of life. The condition can also be frightening and upsetting for the children who suffer from it. Moreover, severe amblyopia persisting in adulthood is a significant risk factor for blindness in the case of an individual losing sight in the good eye. A UK national survey (published by Rahi and colleagues in the Lancet in 2002) identified 370 patients during a 2-year period who had suffered vision loss in the non-amblyopic eye, 86 of whom were severely visually impaired or blind.
To date, no treatment is available to restore normal vision in an amblyopic eye after the age of around 8 years, the end of the critical period of visual brain development.
The aim of the Cardiff University study is to better understand this critical period in early life when the visual cortex in the brain adapts to the signals coming from the eye. It is true that animal experiments using similar methods to manipulate their visual experience have been conducted in the past. However, this is the first time we have been able to obtain both images of visual brain function and to quantify some of the key molecules controlling the critical period of visual cortex development. In the long term, the aim is to use this improved understanding of the brain to treat older children or adults, whose amblyopia has been missed or not treated adequately in time, by creating similar conditions in the visual cortex to those which exist during early childhood.
Cardiff University completely rejects the accusation that this experiment, which was completed in 2010, is cruel or unnecessary. The purpose of the work and its conduct was approved by both the University’s own ethical review process and the Home Office Animals in Science Regulation Unit as part of the licensing process. The University had to establish that the research would reveal new information that could not be obtained in any other way. Cats had to be used for this study because - apart from primates - they are the only mammals with frontally positioned eyes and therefore the only animals to develop severe amblyopia similar to humans under similar circumstances. It is impossible to use any other kind of technique for this study. Claims that this research can be replaced with CT scans or computer models are simply not true. The University will always use alternative technology where it exists and only uses animals when absolutely necessary.
While a treatment for older children may be some time away, Cardiff University believes this research raises the prospect of markedly improving the sight of sufferers of this serious condition.
Research involving animals
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