How does high myopia choose appropriate lens? Lens is too thick can affect beautiful, after how to make his eye wears glasses, does individual character appear comfortable?
The lens material
Lens materials mainly include glass, resin and PC (polycarbonate). The main disadvantage of glass lens is the heavy lens, especially in high myopia, which leads to a significant increase in the pressure of glasses on the nose root and back of the ears of patients, and people who wear glasses often cannot tolerate it.
The latter two lenses have been widely used in recent years because of their characteristics of light texture and strong plasticity, occupying the absolute share of the lens market. High myopic tablets to choose the latter two is appropriate.
The refractive index
Refractive index refers to the refraction ability of the lens to light and is the main parameter to indicate the thickness of the lens. The colophony lens refractive index on the market is in 1.49-1.74 between commonly at present, refractive index is taller lens is thinner, of 1.60 above call ultra thin lens.
To high myopia, should choose the lens with high refractive index as far as possible, but because make craft and material concern, the lens price of high refractive index is often taller. Therefore, it is necessary to select appropriate high refractive index lenses based on price factors. Generally, lenses with refractive index above 1.60 should be selected.
A special type of lens
High myopia should choose lenses with aspherical design. The aspherical lens has a specific centrifugal position, that is, the lens gradually flattens from the center to the edge, and gradually reduces the curvature, so as to reduce the extreme diopter and astigmatism of the edge. Therefore, aspherical lenses are 10%-30% thinner than ordinary lenses with the same number of diopters, and the aberration of aspherical lenses is only 1/5 of that of spherical lenses. Therefore, aspherical lenses can see naturally and enlarge evenly without deformation.
Aspherical lenses are usually made of resin because of the difficulty of grinding and high cost in making aspherical lenses with glass sheets. At present, most of the lenses with high refractive index are made of aspheric surface, which is exactly consistent with the above-mentioned lens materials and refractive index selection.
Of course, due to the limitations of current manufacturing technology and inherent characteristics of lenses, we cannot fundamentally eliminate the shortcomings of lens thickness and poor imaging quality caused by high diopter number. So, optometrists need to know. Be good at communicating with patients to gain their trust and improve the success rate of lens allocation.