Unlike regular contact lenses, Orthokeratology lenses only need to be worn at night. (Image: Techno-Lens)
Reading aloud With special so-called Ortho-K lenses for the night, wearers can compensate for their vision problems for a few hours and then no longer need glasses during the day. Many users are enthusiastic, but some can not cope with the visual aid. If you are a short-sighted person who does not want to wear glasses, you only had two options: contact lenses or a laser surgery in which the cornea is planed down to the nearest millimeter, thus largely correcting myopia. In addition to lenses and lasers, a third method is now spreading: the so-called orthokeratology lenses. With these special hard contact lenses, the cornea of ​​the eye is modeled overnight as a putty and pressed into shape so that the day is seen without visual aid sharp. The deformation of this transparent protective layer over the pupil persists until the evening and thus also clear vision.

The idea of ​​Ortho-K lenses is already several decades old. But only with technical improvements, they gradually turned into an alternative for laser surgery. "Since the end of the nineties, four-curved lenses have been used, which are made of highly oxygen-permeable plastic, " explains Gerald Böhme, ophthalmologist in Backnang near Stuttgart. "The charm of the method is that the change in the cornea can be reversed. In contrast, laser therapy irretrievably changes the eye, "explains Böhme.

Some months after discontinuing the Ortho-K lenses, the cornea bulges back to its original shape. Then you can switch back to glasses or conventional contact lenses. "The Ortho-K lenses are particularly suitable for patients who do not want to wear daily lenses or glasses or do not tolerate well. This is the case, for example, in some occupations in a dusty environment, such as bakers. However, only myopia can be compensated for up to 4.5 dioptres, "says Böhme.

Whether the hard special lenses feel comfortable at night and also do not disturb sleep, everyone has to try for themselves. "About a quarter of the patients who test the lenses set them down again, " reports Andreas Berke, a lecturer at the Höhere Fachschule für Augenoptik in Cologne. The rest, however, are satisfied. display

In a study with 100 ortho-K wearers, Berke was able to show that the visibility hardly declines during the day. For a long time this was considered controversial. Critics had suggested that vision would decrease so much during the day that patients endangered the traffic. "Visual acuity only changed by a quarter of a diopter by the evening in our study. That's so little that many do not even notice it, "says Berke. About half of the subjects had to use the lenses only every other night to see sharp on the following two days.

"However, the Ortho-K method is unsuitable for driving at dusk or at night - regardless of whether the lenses are currently being worn or not, " Berke curtails. Because similar to a laser surgery, the special lenses in the dark light are wrongly detected. Taillights, for example, often appear twice, and the distance of an approaching vehicle often can not be properly estimated.

Since the lenses deform the eye surface with millimeter precision, they must be adjusted very precisely and individually. For this purpose, the curvature of the cornea is measured exactly and then first made a trial lens. "Often the lens has to be readjusted once or twice so that it fits tightly like a suction cup", emphasizes Böhme. This is the only way to ensure that the lenses do not slip off the pupil at night and yet remain free to move.

Despite this individual customization, it can happen that the lens sticks to the eye in the morning and can no longer be loosened. Under no circumstances should the lens be removed by force, otherwise the cornea may be injured, warns Böhme. First, wetting drops should be dropped into the eye to lift the lens with the liquid again. If it still can not be moved through the closed eyelid, it must be removed by the ophthalmologist under local anesthesia.

"We do not know how often Ortho-K lens sticking occurs, as there are no long-term studies, " Böhme admits. "But the lenses have the potential to evolve. They will probably continue to spread in the coming years, "he says.

Currently, however, the price is likely to prevent many defective eyes from making friends with the new visual aid. A pair including individual adjustment costs 200 to 300 euros. In addition, about 50 euros for the monthly examination at the optometrist or optician. The statutory health insurance companies do not yet support the method.

ddp / science.de - Susanne Donner

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