Polycarbonate Lens: Polycarbonate lenses are the most impact resistant lenses available and are always the lens of choice for young people and active patients. Polycarbonate lenses are high index and are usually the lightest, most comfortable lenses. They absorb all harmful UV light and can be made with ultra thin edges because of their unique strength.
Hi-Index Lens: Modern technology has created lenses that bend light differently so that stronger corrections are thinner than when made in conventional materials. Such lenses are called "high index" lenses. These types of lenses are suitable for person who has high power. These lenses are more attractive because they are slimmer. Glass lenses are also available with the slimming advantages of High index but are considerably heavier. High index plastic uses less material so they are often lighter in weight. High index lenses absorb all harmful UV light and can be tinted to any shade or color.
Photochromic lens: Photochromic lenses are lenses that darken on exposure to ultraviolet (UV) radiation. Once the UV is removed (for example by walking indoors), the lenses will gradually return to their clear state. Photochromic lenses may be made of glass, polycarbonate, or another plastic
Glass Lens: For years glass was the only lens material available and still it offers superior optics. These type of lenses are the most scratch-resistant material. The primary disadvantage of glass is its weight, generally twice that of platic lenses. Glass lenses are heat or chemically treated to increase impact resistance.
Bifocal Lens: Bifocal the upper part of the lens is generally used for distance vision, while the lower part is used for near vision. Usually, a segment line separates the two. Typically a person with myopia would have one section of a prescription lens that has a certain diverging power while another section of the lens would have a lower diverging power for close-up work. Similarly a person with hyperopia would have one section of the lens with a certain converging power and another section with a greater power for close-up work.
Trifocal Lens: Trifocal lenses are similar to bifocals, except that the two focal areas are separated by a third middle area with intermediate focus correction, used for intermediate vision, e.g. computer distance. This lens type has two segment lines, dividing the three different correcting segments.
Progressive lens (no line bifocals): Progressive or varifocal provide a smooth transition from distance correction to near correction, eliminating segment lines and allowing the viewing of all intermediate distances.These lenses provide all the benefits of bifocals but add the feature of continuous clear vision at all distances, including mid-range distance (arm's length). Progressives have the cosmetic advantage of appearing to be single vision lenses so they never reveal the user wears bifocals. Progressives are available in all lens materials and also made in aspheric form. Because of their many benefits, they are the lens of choice for bifocal and trifocal wearers.
Aspheric Lens: Aspheric lenses are typically designed to give a thinner lens, and also distort the viewer's eyes less as seen by other people, producing better aesthetic appearance. These new lenses provide special visual and cosmetic benefits for stronger corrections and increase edge to edge clarity. Flatter than conventional lenses, aspheric lenses eliminate the "bulgy" appearance of strong plus lenses (far-sighted corrections) and greatly enhance the appearance of finished eyewear. People with strong nearsighted corrections also benefit from thinner, lighter weight glasses when their lenses are aspheric. Because aspheric lenses are positioned closer to the face, there is less eye magnification with farsighted corrections and less "small eyes" look with nearsighted corrections. Aspheric lenses are often made of high index materials for the ultimate in thin lenses.
Anti Reflection Coating: Anti-reflective coatings help to make the eye behind the lens more visible. They also help lessen back reflections of the white of the eye as well as bright objects behind the eyeglasses wearer (e.g., windows, lamps). Such reduction of back reflections increases the apparent contrast of surroundings. At night, anti-reflective coatings help to reduce headlight glare from oncoming cars, street lamps and heavily lit or neon signs. One problem with anti-reflective coatings is that historically they have been very easy to scratch. Newer coatings, such as Crizal Aliz with its 5.0 rating and Hoya's Super HiVision with its 10.9 rating on the COLTS Bayer Abrasion Test (glass averages 12.14), try to address this problem by combining scratch resistance with the anti-reflective coating. They also offer a measure of dirt and smudge resistance, due to their hydrophobic properties
UV Protection Coating: A UV coating is used to reduce the transmission of light in the ultraviolet spectrum. UV-B radiation increases the likelihood of cataracts, while long term exposure to UV-A radiation can damage the retina. DNA damage from UV light is cumulative and irreversible. Some materials, such as Trivex and Polycarbonate naturally block most UV light and do not benefit from the application of a UV coating.
Scratch Resistance Coating: Highly recommended, especially for polycarbonate and softer materials, to make lenses last longer. This is done automatically by many labs for polycarbonate and high index lenses.