Uncovering the materials for the lenses of glasses

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Lens thickness in glasses is influenced by many factors, among which lens power is the main factor. The Lens thickness of High Myopia is thicker than that of low Myopia. However, when it comes to overall thickness, the diameter of the Lens is also important, and choosing a smaller frame can significantly reduce the thickness of the Lens. The shape of the Lens is also important, such as Myopia in the thick peripheral part of the concave Lens, Hyperopia in the thick central part of the Convex Lens and thin peripheral.

The refractive index (June 20) of a lens is a critical characteristic and a factor that allows the patient to control the thickness of the Lens. Refractive index is the ratio of the rate at which light passes through a particular medium (such as glass, water, plastic, air) to its rate in a vacuum. The higher the refractive index, the lower the transmission rate of light in the medium, and the more obvious the refraction of light. Thus, a lens with a high refractive index refracts light more efficiently and is therefore thinner than a lens with a low refractive index.

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Glasses have been made of glass for centuries, and some patients still insist on glass lenses because they feel they give them the best visual quality. Modern glass lenses are made from Crown Glass, a material with low chromatic aberration and resistance to scratching. Crown Glass has a high refractive index, even higher than that of many plastic lenses. However, because of its high density, crown glass is heavier than plastic lenses with the same refractive index, even though plastic lenses are usually thicker. Patients tend to choose lighter lenses, which is why they choose plastic lenses over crown glass.

The Standard Plastic for frame glasses is Columbia Resin-39(CR-39) . This is a good lens material, scratch-resistant, and weighs only half as much as the same glass lens. However, its low refractive index means that the Lens is relatively thick when made into high-diopter glasses.

A variety of plastic lens materials have been developed, resulting in a higher refractive index but thinner, lighter lenses. Such as polycarbonate (1.586) , polyurethane (1.595) and even special materials glass (1.70) . These lenses are no thicker than those of other myopic patients, while providing a higher number of degrees of height. However, some of these materials have larger aberrations than low refractive index materials and are not easily tolerated. Most of these materials are softer, more resistant to breakage than glass or CR-39 plastic, but more prone to scratching.

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Post time: Jul-28-2021