High Index Lenses
Small diopter of lenses are quite thin and light, they do not distort the image. But at high degrees of myopia and hyperopia needs a large optical power of the lens. Such lenses are thick and heavy.
When myopia lenses are thicker at the edges, with presbyopia - a central part. The negative lens diopters great fit not all frame - users have to select those models that hide the thick edge of the lens. On the frame with screws or fishing line can not be considered. In addition, a large optical power of the lens is visually significantly change the size of your eyes: Positive increases and minus - reduced. Heavy glasses uncomfortable to wear, they put pressure on the nose, leaving prints.
Thin High-index lenses
Attempts to make the lens thinner led to the development of "high-index" material for eyeglass lenses - materials with higher refractive index than that of a standard glass and plastic. Lens with a higher refractive index will always be thinner than the optical lens of the same power, but with a lower index. High lomu lenses considered materials with a refractive index of 1.59 or more. The higher the index of refraction of the material, the thinner is the lens, and aesthetic.
Mineral glass may have a refractive index of up to 1.9, but with an increase in the index of refraction also increases the proportion of glass, so the glasses, even very thin, will be very heavy.
The refractive index of the optical polymers varies from 1.5 to 1.74. A lens produced from a material with a refractive index of 1.7, for example, will be nearly two times thinner than the traditional polymer lens with an index of 1.5.
The advantage of high-index plastic lenses is also their low weight. Thus high lomu spectacle lens is not only thinner than conventional, but also considerably easier.
Typically, a lens with a high refractive index of the optical power available at points 3-4 diopters. While some users choose high lomu materials at lower diopters, want to be as thin and light spectacle lenses.
Design and cover of High-Index Lenses
Most thin and weightless lenses are obtained by a combination of high quality material with an aspherical design. From high-index materials can be made any spectacle lenses: single vision, bifocal, progressive, photochromic, colored, with protection from ultraviolet and electromagnetic radiation, etc.
It is desirable to have a high-index lens antirefleksnoe antireflection coating as the optical material with a high refractive index reflects 50% of light falling on them. Antireflective coating makes the lenses more transparent, increases the contrast ratio and eliminates glare.
Because of their merits the lenses with a high refractive index are more expensive lenses which are made from conventional materials. The higher the refractive index, the higher the price of the lens. But for many people who are forced to wear a bulky heavy glasses to choose whichever eyeglasses, the ability to wear glasses with thin and light lenses appealing more than compensated higher cost.