Health: The future is blurred
Half of us could be short-sighted soon - and it may be an evolutionary consequence of modern lifestyles. Roger Dobson looks at a worrying development, while Eileen Fursland (below) finds a new surgical procedure offers hope to the blind
Thursday 20 May 1999
In Britain, one in three people is short-sighted, and in parts of the Far East more than 90 per cent of university graduates are sufferers. In Singapore, the problem is so acute that the air force has had problems in recruiting flyers, because of a lack of graduates who can meet the necessary vision requirements.
"The increase has been dramatic in some areas, to a point where the vast majority of the population is now short-sighted," says Dr Flitcroft, an ophthalmologist who has carried out research into the focusing mechanism of the eye.
"Eighty five per cent of schoolchildren in Taiwan are short-sighted. In Singapore, they had to alter the regulations covering short sight in the air force because by the time they graduated and completed five years of training, recruits were short-sighted. In the US, the latest study shows that it is heading towards 45 per cent. That compares to about 20 per cent in the earlier part of the century, and studies of families have also shown that the younger siblings tend to have more myopia. In parts of the Far East where eye tests are compulsory at 18, it's been found that the prevalence of myopia is increasing in less than a generation."
No one really knows why this increase is occurring, although there are various theories. The dominant view is that the modern lifestyle, with its demands for close work, is to blame. The latest suggestion is that exposure to nightlights in infancy may be responsible for physical changes in the eye. Another theory is that myopia is an evolutionary inevitability, and that the eye is adapting to changing circumstances.
In the past, man's dominant need was for good distance vision, but with eight or more hours a day now spent in close work, the eye is giving priority to near sight.
Short sight occurs when the curvature of the cornea is too steep or the eyeball is too long. As a result, light rays come to a focus in front of the retina rather than on it, as it would with perfect vision. The myopic sees near objects clearly, but distant images are blurred.
It was once thought that short sight was solely an inherited problem. Genetic factors do play a role, but the trigger for most myopia is now considered to be an environmental one. That would explain why the rates of myopia in Britain soar from 2 per cent in five-year-olds to up to 40 per cent in adults.
The finger of suspicion points at close work, in particular reading, and the increased use of PCs and computer games. The move towards sedentary pursuits means that children are spending less time playing sports and games, which require distant vision, and this compounds the problem.
A study of Eskimos found that the number of people with myopia increased from 2 per cent in one generation to 45 per cent in the next generation. There had been no changes in diet or lifestyle, but the researchers concluded that their deteriorating eyesight was due to a shift in educational practices. The oral tradition of Eskimo schooling had been replaced by formal, written education, with several hours a day of reading and writing.
Another survey, of Orthodox Jews, found that men had much higher rates of myopia than women. This was blamed on the fact that the men spent several hours a day, from an early age, reading religious texts (and the women didn't).
It is now thought that there may be some kind of trigger mechanism that makes the eye grow longer in response to the demand of close work, and it doesn't take long for harmful effects to occur. A British study revealed that workers who spent eight hours day looking at samples through microscopes became myopic after just two years.
"The researchers measured the eye lengths of these adults when they started the job, and went back a few years later and a third of them had become myopic; their eyes had ended up too long. Within two years, the eyes had started to change," said Dr Ian Flitcroft.
"There is no doubt that near work is much the most intuitively plausible explanation," confirms Dr Richard Wormald, an ophthalmic epidemiologist and consultant surgeon at Moorfields Eye Hospital. "Human beings are extraordinarily adaptive to their environment, and if you spend most of your time focusing on near objects the eye will adapt. The amount of time children spend studying has increased compared with even a few years ago."
Much of the research has concentrated on the Far East, because of the high rates of myopia in urban populations compared with rural areas. "What is different and quite remarkable about the Far East is the amount of school work done by children, six hours at school and another six hours' homework. Teenage homework diaries there are quite outrageous," says Dr Ian Flitcroft. "The highest incidence of myopia ever recorded was in Singapore, where 98 per cent of medical graduates were found to be myopic. We know that only about 2 per cent of children are myopic at the age of five, so that is a huge increase."
The latest theory, from the Philadelphia Children's Hospital, is that nightlights can damage your eyes. Children who have nightlights during their first two years were up to five times more likely to be myopic. Researchers are not certain why, and the results may have been confounded by other factors. Parents who give their children nightlights, for example, may be more likely to encourage them to read and study, too. Fearful children who need nightlights may also be more imaginative and more likely to be avid readers.
Myopia is currently alleviated with contact lenses, glasses or corrective surgery, and each option has its drawbacks. Any surgery has associated risks, and there are no guarantees that the eye will not deteriorate again later.
Contact lenses are not suitable for small children, and may leave the eye vulnerable to infections if they are not correctly handled. Glasses will not cure deficiencies and may even worsen the existing complaint. It has been suggested that using spectacles as a visual aid thwarts the eye's own corrective processes.
Studies have shown that if an animal with normal eyesight is given glasses, its eyes will adjust so that when the glasses are removed the animal has become myopic.
However, new research being carried out in America may offer a preventive solution and help to reverse the current trend. Researchers have recruited 469 children aged from six to 11, half of whom will wear special bifocal glasses for the next three years. It is hoped that these will prevent their eyes from changing shape. If successful, it could fundamentally change the way we use glasses. Instead of being a visual aid, they could offer a cure for myopia.
Eyeball to Eyeball
n The cornea serves as the main lens of the eye and performs most of the focusing. It is wide-angled and permits a 180-degree range of vision.
n Nerve cells in the eye convert an image into electrical impulses. These are carried by the optic nerve and then interpreted by a specialised region of the brain.
n If, for any reason, the eyes are not used in the first few months of life, the surrounding structures will not develop properly and the eyes will be permanently blind.
n The eyeballs are embedded in pads of fat, within the orbits. The orbits are bony cavities in the skull that protect from injury.
n Eyebrows and eyelashes help to prevent sweat from your forehead dripping into your eyes.
n In the mid-forties, eyes start to lose their focusing power, and it may become harder to read comfortably. This is known as presbyopia (from the Greek word presbos, meaning old man).
n Six tiny muscles called extraculor muscles move each eyeball.
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