High Index Eyeglasses
High Index glasses use a specially designed lens material that has a much higher refractive power than traditional glass or plastic lens types. The greatest advantages high index eyeglasses have is that they require significantly less material than glass or plastic glasses require, allowing people who have severe vision errors to wear glasses without thick cumbersome lenses.
For further weight and size reduction, many high index lenses use an aspheric lens shape, which can combine with the high index material for a significant size reduction and overall improvement in optical clarity. By using aspheric shapes, high index eyeglasses also can take advantage of material with higher refractive properties without risking edge distortion and blurring.
High Index Materials and Measuring Refractive Quality
Any given lens will refract light to a certain degree. With greater refractive power, less material and less curvature is needed to correct one’s vision problems. Standard plastic lenses have a refractive value around 1.498, and any lens with a refractive index greater than 1.523 qualifies as a high index lens variety. While 1.523 qualifies as high index, the majority of high index glasses range from strengths of 1.54 to 1.74, with the most popular value being 1.67. Lenses at the high end of the refractive index require no more than half the material a normal (1.498) plastic lens would, and when combined with aspheric shaping, are extremely thin and light.
How do High Index Lenses Work?
Achieving higher refractive strength is accomplished via manufacturing denser material. Due to higher density, light is forced to pass through more material prior to reaching the eye. Because of this, the light experiences a greater amount of refraction than it would if it were to pass through a less dense lens. While most high index lenses are made from polycarbonate materials, some designers use specially designed high index glass and plastic materials for their lenses. While it’s rare to see high index materials with greater refractive qualities than 1.74, it is possible to make certain types of high index lenses that have a refractive property greater than 2.0, although lenses with refraction this high aren’t particularly practical for an every day glasses wearer.
High Index Glasses Overview
High index glasses can be made to correct almost any traditional eye problem, including Hyperopia, Myopia, Astigmatism, and Presbyopia. Since high index typically refers only to the lens material itself, high index glasses may also be classified as bifocal, multifocal, aspheric, or any other type of glasses. This allows everyone to experience the benefit of high index lenses without restriction.For people who wear bulky glasses however, the price is worth the benefit if it means wearing lightweight, thin eyeglasses. As can be expected from more complex materials, high index lenses cost more to manufacture than standard eyeglass lens types, and will generally cost more for a consumer to purchase.
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