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Night lenses to correct myopia

21 Nov 2010
Night lens (Ortho-K lenses) are used to correct nearsightedness. They put on the night and in the morning shoot. This provides good vision during the day without contact lenses and glasses. This method of correction is known as Orthokeratology, and based on the effect of "forming" the cornea.
For the first time the effect of "formation" of the cornea was found in the forties of the twentieth century when wearing scleral contact lenses. After the appearance of corneal contact lenses, in the fifties, experts NERF (National Eye Research Foundation, USA) suggested that this effect may be useful for patients if it is safe and controllable.
George Jessen (George Jessen) in the sixties of the first to propose the construction of Ortho-K lenses made of polymethylmethacrylate, which he called "ortofokus." This lens did cornea flatter in the middle, which reduced short-sightedness. Shortly thereafter, Wesley Newton (Newton Wesley) coined the term "orthokeratology". But at that time the effect has been very unstable and insignificant, poorly predictable, but achieving it takes weeks, sometimes even months. Therefore orthokeratology was seen as a kind of "shamanism". However, work in this area continued, and in 1968 opened as part of the international department of NERF Orthokeratology (IOS, International Ortthokeratology Section), which exists to this day.
The emergence in the late seventies gas permeable materials significantly increased the safety of contact lenses, even though not all the problems have been solved in orthokeratology. The situation changed when in the late eighties - early nineties appeared coordinate precision lathes with numerical control. Such machines have made it possible to make the lens inverse geometry, in which the center is more flat compared with the periphery, whereas in conventional lens design is reversed. The idea of ​​such a lens was proposed by George Jessen, but the first real design developed by the American ophthalmologist Vlodiga Richard (Richard Wlodyga). Made such a lens was Stoyan Nick (Nick Stoyan), which is currently president of the company Contex Inc.
The mechanism of such a lens is based on the principle of spherization Dr. Mountford, who is known as the theory of the "pressure of the compressed layer."
When the lens is placed on the surface of the cornea, lacrimal layer is compressed between the lens and the cornea. This layer creates a negative force ("thrust") in those places where it is thick, and the positive force (pressure) where it is the most subtle, to achieve balance over the entire surface of the liquid layer.
The corneal epithelium has a thickness of 50-60 microns, and consists of 5-6 layers of cells, which are able to move. Modulus epithelium is much less than in the stroma, and rigid lens does not change shape. Lacrimal layer is incompressible and produces additional forces (forces compressed layer), which are unevenly distributed between the two surfaces. As a result, the epithelium, as the movable component of the system is moved.
In other words, due to the complex configuration the inner surface of the lens are mikrokapilyarnye force inducing dosage and predictable migration of the surface layers of the corneal epithelium. Change the topography of the anterior corneal surface and its thickness, allows you to change the refractive power of the cornea on the calculated value.
The refractive effect is due not only to the decrease in the thickness of the epithelium in the center, but with the increase of its thickness in the mid-peripheral zone. The cumulative effect of these small changes in the shape very significant.
During the last decade a number of companies have developed reverse geometry lenses of different designs. He coined the term "accelerated orthokeratology", referring to the selection of these lenses.
Indications for refractive therapy is:
- Nearsightedness up to minus 7 diopters;
- Astigmatism of 1.75 diopters up;
- The progression of myopia.
Contraindications refractive therapy:
- Internal violations of the eye;
- Any abnormality of the cornea;
- Dry eye syndrome.
Initially, reverse geometry lenses are recommended for daily wear, but in 1993 there were the first works on overnight wear. This became possible with the advent of high-performance materials with high gas permeability.
However, that would provide greater oxygen permeability of the lens, it is necessary to increase the content in the silicone material. Since silicone soft material, then provide the necessary rigidity can only increase in the fluorite content of any acrylic. But it makes a thick lens and deprives its surface harmony.
Paragon Company for nearly 10 years engaged in the development of materials with high purity silicon from the ballast (the three studies were conducted in conditions of weightlessness on satellites Shatll) and created material paflyufkon, with an optimal ratio of fluorite and highly purified silicon having a high koslorodopronitsaemostyu. Paflyufkon developed based on membrane technology. Due to this lens with high rigidity is very thin, which makes it possible to harmonize its surface, dividing function - the optical front and rear (internal) activity. It is also apparent that the thinner the lens, the greater its kislorodopronitsamost.
The principle of operation of such a lens is that the night lens gradually changes the shape of the cornea. After removing the lens in the morning, the cornea retains its new shape that provides a clear vision all day long. The use of night lenses gives temporary results. Removing the lens in the morning, you see well only until the evening. At night you need to wear lenses again. This is due to the fact that the previous form of the cornea recovers in a few days and returned to its original vision. With regular use of Ortho-K lenses, a couple of months they can not wear all the time, determining the frequency of their own. However, every six months is necessary to diagnose view. Results from the use of such lenses is comparable with the result of surgery.
Night lens can pick up by a qualified expert. The service life of such lenses about two years. They are durable and are not afraid of drying. Ortho-K lenses do not require such delicate care as soft contact lenses. The use of night lenses when used correctly and safely care, as well as the wearing of contact lenses.
The advantage of using a recovery night lenses maximum access of oxygen to the cornea. It is known that contact lenses cover the cornea most of the time, and only at night eye "breathes" fully. Application of Ortho-K lenses gives the opposite possibility: the day the cornea "breathes" and at night it is closed gas permeable lenses.
I especially recommend the night lens myopic children, as this method of correction stops falling. The main advantage of the Ortho-K lenses in this case, the safety of children's eye health. After all, the child is difficult to take good care of glasses, and even more so with contact lenses. A surgical operation, restoring sight, forbidden to eighteen years. In the evening, children are under parental control, so timely and properly wear such lenses.
Another feature of the Ortho-K lenses - their application in order to correct the result of unsuccessful surgeries. In this case, the lenses prescribed for daily wear.
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