Thick Lenses Made Thinner
The trend in technological advancement is to make things smaller and thinner than they previously were.
Thick Lenses Made Thinner
Computer-chip motherboards that were once the size of suitcases are now the size of a fingernail. Televisions have morphed from tube-run behemoths that were a couple of feet thick just two decades ago to flat-screens thin enough to mount on the wall. Cell phone thickness can now be measured in millimeters.
So what about corrective lens thickness? Strong prescriptions require the production of very thick, very heavy lenses, with the obvious disadvantages they bring. The technology to form glass lenses worn over the eyes to correct for vision inaccuracies has been around for literally many hundreds of years. So where’s the big breakthrough that allows for thinner glass or plastic lenses?
It is finally here, in the form of high index lenses…“finally,” in this case, being a relative term, since high index lenses have been around for decades. They’re now a proven technology but are “new” to the millennia-old eye-wear industry. High index lenses, available in either the plastic or glass format, combine and compress layers of this material in such a way as to give it a higher refractive index than standard glass or plastic. High index lenses are defined as any lenses made from a material with a refractive index higher than 1.6.
This advancement has a very practical advantage. Eyeglass lenses work by refracting, or bending, light as it passes through the eyeglass lens. Your corrective vision prescription determines the curvature your lenses will need to refract incoming light rays at the angle your eye’s natural lens will require for clear sight. Since high index material has a higher refractive index, it can form that curve using less physical glass or plastic than lower-index material. This makes high index lenses lighter and thinner than low index lenses.
That reduction in physical material can be significant, especially in the case of very strong prescriptions. The stronger your prescription, the more curve your corrective lens will require; a high index lens in a strong prescription can be several times thinner than an identical prescription formed of lower-index materials. For instance, lens material that has a refractive index of 1.6 will be approximately 25% thinner than a 1.5 index lens. 1.67 will be 40% thinner than 1.5, and 1.7 will be 50% thinner than the 1.5. The highest high index material currently available is 1.9, which is 75% thinner than 1.5 index material.
Isn’t technology great?