London - Rebecca Large has always been told her big brown eyes are her best feature. Like those of Hollywood stars Angelina Jolie and Audrey Hepburn, Rebecca’s eyes are regarded by most as a sign of beauty.
Yet eye experts have realised that far from being an asset, large eyes can actually be a weakness, and make someone more prone to being short-sighted.
This condition, also known as myopia, causes distant objects to appear blurred, while close ones can be seen clearly. It is caused by light not properly reaching the retina, the light- sensitive area at the back of the eye.
Experts believe this might be because the eyeball grows too large, which causes the light to focus in front of the retina, rather than on it.
“It’s so ironic, people often remark on what big eyes I have like it’s a good thing - but actually I’m as blind as a bat,” says Rebecca, 30, a design assistant who lives in Ealing, West London, with her boyfriend Gavin, 28, an engineer.
Rebecca needed glasses at the age of 15, and now is severely short-sighted, with a prescription of minus ten (perfect vision is classified as zero).
“I can’t see further than my hand if I hold it in front of my face unless I’m wearing my glasses,” she says. “I can’t wear contact lenses or have corrective laser surgery as I have another eye muscle weakness condition and it’s meant that I’ve had to be a lot less adventurous in life than I would liked.
“I can’t really swim far because I can’t see well enough without my glasses and a specialist advised not to try bungee jumping because my short-sightedness puts me at higher risk of a tear in my retina.”
Short-sightedness is on the rise in Britain, with up to 50 percent of people now estimated to have it.
One possible explanation for this is that our eyeballs are getting larger because we are spending more time indoors. A lack of outdoor light in our early years causes the size of the eyeball to increase. But the larger the eyeball, the more likely a person is to be short-sighted, explains Andy Luff, a consultant ophthalmic surgeon at Optegra, a chain of private eye hospitals.
“While big eyes can certainly look beautiful, the fact is that if your eyes are slightly too big, this will cause you to suffer short sight. If the eyeball is too big, the light focused by the lens of the eye does not reach the back the retina, where images are processed.
“If the eye is only 1mm longer than 24mm (the average size from front to back) a person will be significantly short-sighted. Longer than the average by 2 to 5mm will make you highly short-sighted.”
Dr Luff explains that in the past we thought the eye grew too large and became short-sighted due to genetic factors.
“Although genetics is still the most important reason behind short-sightedness, lack of exposure to outdoor light is another possible cause. And it’s the one preventable cause which can be addressed in childhood.”
Our eyes usually reach their full size by our 20s. The ideal is that they stop growing at the right size and will have perfect vision, but if they grow too big they’ll be short-sighted and if they don’t grow enough they’re long-sighted, and won’t be able to see things close up. Some children can have eyes that are too large by the age of five, says Dr Luff.
“We now know that if the eyes are deprived of outdoor light, they grow bigger than is needed,” he adds.
Rebecca believes too much time spent indoors in her younger years could be to blame for her poor eyesight, as neither of her parents are short-sighted. An academic child, she spent her years buried in books before going on to study archaeology and anthropology at Oxford.
“I did a lot of reading and studying as a child,” she says. “I loved history and evolution and read constantly from the age of ten and through secondary school, preferring to stay indoors, rather than play outdoors.”
And increasing evidence is supporting the theory that this lack of time outdoors may have contributed to her short-sightedness.
A review published by the University of Cambridge in 2011 found that for each additional hour spent outside each week, the risk of short-sightedness was reduced by two percent. The review of studies involving 10 000 children and adolescents found that short-sighted children spent on average 3.7 fewer hours per week outdoors than those with normal vision or long-sightedness.
And another study, led by Dr Kathryn Saunders, reader in vision science at the University of Ulster, found children in Northern Ireland were three times more likely to be short-sighted than Australian children. She suggested this could be due to the protective effect of the sunnier southern climate.
“As far as we could tell, all other factors were equal between these children,” says Dr Saunders. “The amount of time spent outdoors in the sunshine could be the explanation for why rates of short-sightedness differed so much.”
But how could exposure to light change the shape of the eyeball? Dr Saunders suggests that natural light in the eyeball flicks a type of biological switch that prevents it from growing too large. However, artificial light is not strong enough to flick this switch.
“The hypothesis is that exposure to outdoor light increases levels of a natural chemical in the eye called retinal dopamine,” she explains. “This chemical inhibits eye growth - so the light stops the eye growing too big and becoming short-sighted.”
She adds: “Prevalence of short- sightedness is on the increase and has occurred too rapidly to be due to genes alone.”
Short-sightedness is not only inconvenient, though - all forms of it carry major increased risks of developing other eye diseases, some of which can even result in blindness.
“Short-sightedness also puts you at higher risk of other eye diseases, including torn and detached retinas, glaucoma and macular degeneration,” says Mr Luff.
The risk of torn or detached retina is thought to be higher because the jelly inside the eyeball is more likely to shrink and pull away from the back of the eyeball, damaging the retina. Why a large eye increases the risk of glaucoma and macular degeneration is still unknown.
He adds that light only changes the shape of the eyeball in our youth - once we are past our teens the size of the eyeball is fixed.
“Once the eye is fully grown - usually by your 20s - spending more time outdoors won’t make any difference to whether you’re short-sighted or not. If we can help prevent short-sightedness or the severity of it by advising parents to encourage their children to play outside more and gain exposure to the sun, then it has to be a good thing.”
People with small eyes tend to be long-sighted and will have difficulty seeing close objects clearly because light rays are focused behind the retina.
But this tends to be largely genetic. “Too much outdoor light will not make your eye long-sighted,” says Mr Luff. He adds that short-sighted people seem to suffer more complications than those who are long-sighted.
“We see far more associated eye health problems in the short-sighted than the long-sighted, so it’s worth doing everything you can to try and prevent it,” he explains.
However, Dr Susan Blakeney, clinical adviser to the College of Optometrists, says there could be other factors contributing to why our increasingly indoor lifestyles may be causing bad eyesight.
“We still don’t know what it is about time spent outside that has a protective effect against short-sightedness - it could be the sunshine, the brightness of the light or the fact that objects you focus on tend to be farther away outdoors.”
And Dr Bernard Chang, a vice president of the Royal College of Ophthalmologists, adds that while the majority of people who are short-sighted will have large eyes, they won’t always appear big on the face, as most of the eyeball is not visible, and is behind the eye socket.
Andy Luff says that the colour of the eye and shape of the eyelid can also influence how large someone’s eye look.
In rare cases short-sightedness can also be caused by the curve of the cornea (the transparent part of the front of the eyeball) being too steep.
Rebecca Large just wishes she’d known about the importance of spending time outdoors for preventing short-sightedness when younger.
“If I’d known what lay ahead I would definitely have spent more time playing outside and not so many hours studying books indoors,” she says.- Daily Mail