High Index Lenses

Why can high-index lenses be made thinner?

Eyeglass lenses correct vision by bending light as it passes through the lens. The amount that light must be bent to focus correctly on the inside back of your eye (retina) and give you good vision is determined by the lens prescription. Nearsighted prescriptions decrease light bending ("-" lenses) and farsighted prescriptions increase light bending 
("+" lenses.)

The real secret behind high-index lenses is something called "index of refraction."  A lens material with a high index of refraction bends light more so less of it is needed to produce a given lens prescription. 
 

	High index lenses are usually classified by their  "index of refraction". Generally, the higher the  number, the thinner and lighter a lens will be.  Popular materials today are those with indexes  of 1.60, 1.66, and 1.71. Material with an index
of 1.71 is the thinnest material currently on the market and is normally used for  moderate to high amounts of nearsightedness or farsightedness.

Aspheric lenses

In an aspheric lens, the lens curvature is not constant across the whole lens. The curvature gradually changes from the center of the lens to the edge of the lens. Overall, aspheric lenses have flatter curves. They are thinner and do not appear to "bulge" out of the frame as much as conventional lenses do. While high-index lenses benefit nearsighted wearers the most, they offer significant advantages to farsighted wearers also.

The distance a prescription lens is positioned in front of the wearer's eye has cosmetic ramifications. Strong farsighted lenses tend to enlarge the wearer's eyes, producing a magnified appearance. Strong nearsighted lenses do just the opposite: they minify the wearer's eyes making them look smaller. To decrease both magnification and minification effects, a lens should be positioned as close to the eye as possible. In many cases, an aspheric lens design will result in a shorter distance between the wearer's eye and the lens…resulting in a more pleasing cosmetic effect.

In Conclusion

High index materials provide significant advantages over traditional plastic or glass lenses. They can drastically reduce the thickness of your prescription lenses and are more shatter resistant than traditional plastic lenses. High index lenses absorb all harmful UV light and can be tinted to any shade or color. When combined with an anti-reflective coating, the result is the best-looking prescription eyeglasses that modern science can provide. The next time you order new eyewear be sure to ask about High Index.