High myopia due to the high degree of myopia, generally speaking, the lens is thick, but if the lens is too thick, the wearing time will be too long to press the nose, and the eyes are not comfortable. So, how should high myopia match glasses to be able to both comfortable and correct myopia, alleviate eye fatigue?
One
There are three kinds of lens materials: glass, resin and PC. The main disadvantage of glass lenses is that the lenses are heavy, especially in high myopia films, which leads to the obvious increase of pressure on the nose root and the back of the ear of the patients with glasses, and people who wear glasses are often unable to tolerate it.
The latter two have been widely used in recent years due to their light texture and strong plasticity, occupying an absolute share of the lens market. The best choice of high myopia film is the latter two.
Two
Refractive index is the zigzag ability of the lens to the light, which is the main parameter to express the thickness of the lens. At present, the refractive index of resin lenses on the market is generally between 1.49-1.74. The higher the refractive index, the thinner the lenses are. Those with a refractive index of more than 1.60 are called ultra thin lenses.
For high myopia, the lenses with high refractive index should be selected as much as possible, but due to the relationship between manufacturing technology and materials, the price of lenses with high refractive index is often higher. Therefore, to choose the appropriate high refractive index lens based on the price factor, generally, the lens with the refractive index above 1.60 should be selected.
Three
The aspheric lens should be selected for the special type of high myopia. Aspheric lens has a special centrifugal position, that is, the lens gradually flattens from the center to the edge, and gradually reduces the curvature, so as to reduce the edge too strong diopter and edge astigmatism. Therefore, the aspheric lens is 10% - 30% thinner than the ordinary lens under the same diopter, and the aberration of the aspheric lens is only 1 / 5 of that of the spherical lens. Therefore, the aspheric lens has natural vision and uniform magnification without deformation.
Because it is difficult to grind and high cost to make aspherical lens with glass sheet, it is usually made of resin material. At present, most of the lenses with high refractive index are made of aspheric surface, which is exactly the same as the selection of lens materials and refractive index.
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