CONTACT lenses worn only at night can temporarily correct long-sightedness by altering the shape of the cornea, a small pilot study suggests. The approach could be an alternative to surgery for people who do not want to wear contacts during the day.
The method, called ortho-k or orthokeratology, is already offered by a few clinics worldwide for treating short-sightedness, or myopia. Rigid gas-permeable contact lenses flatten the central region of the cornea, correcting moderate myopia. But when the contacts are removed, the cornea gradually resumes its normal shape, so people must wear the lenses regularly.
Now Helen Swarbrick鈥檚 team at the University of New South Wales in Sydney, Australia, has shown it might work for long-sightedness too. She tested lenses based on a design that was created in the 1970s for normal use but abandoned because of anecdotal reports that their bulbous shape produced an unwanted bulging of the cornea, worsening myopia.
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The test, in which 10 volunteers wore the lenses for 4 hours, showed that they do indeed make the cornea bulge out more. 鈥淭here鈥檚 the potential there for correcting long-sightedness. But we鈥檙e very much at an exploratory stage,鈥� Swarbrick says. 鈥淣ow we need to find out how much of an effect we can actually achieve.鈥� The team plans to design lenses that maximise the bulging effect, while remaining gas-permeable.
Ortho-k lenses for myopia were first developed in the 1960s, but the method took off only in the mid-1990s, particularly in Asia, after better lens materials became available. 鈥淏ut the effect you get with ortho-k is small and temporary,鈥� says Hugh Taylor of the Centre for Eye Research Australia, in Melbourne. And most people barely notice normal lenses worn during the day anyway. He thinks standard LASIK laser surgery is a more effective long-term option.
Some groups have tried to create an alternative to laser surgery by 鈥渇ixing鈥� the shape changes produced by ortho-k lenses (快猫短视频, 16 March 1996, p 23). But this has turned out to be impractical, says Swarbrick.
