If you have a very strong eyeglass prescription, chances are you have fairly thick lenses. Corrective lenses that are thin in the center but thicker at the edge of the lens are common for those who are nearsighted. The stronger the prescription, the thicker the edges tend to be, which can create a number of issues.
The majority of today’s fashion frames are made of plastic or metal with very thin rims. Often the rims are thinner than the lens they are meant to hold. And the popular rimless frames obviously leave the edges of the lenses completely visible. In both cases, the lens edges are highly exposed and can detract from your eyewear’s appearance.
Regular glass or plastic lenses do not always bend light efficiently, meaning they need to be thicker (and often heavier) to produce the needed correction. “High-index” lenses are made of a newer type of plastic that is specially formulated to bend light more efficiently using less material to correct the same amount of refractive error. This makes high-index lenses thinner, lighter, and overall preferable to conventional glass or plastic. Because they are lighter and thinner (20 percent to 65 percent less than standard plastic), high-index lenses are more comfortable to wear and are much more attractive in newer frame styles.
High index lenses are categorized according to how strongly they bend light. The higher the index (between 1.53 to 1.74), the better the lens is at bending light. However, only when prescriptions are over +2.00 or under -2.00 are the benefits of high-index lenses necessary. In weaker prescriptions, the difference in weight and thickness is minimal. As high-index lenses are more expensive than traditional glass or plastic, it isn’t always the best option for people with lower corrective needs.
Polycarbonate lenses also offer many or the same benefits as high-index lenses, but unfortunately polycarbonate lenses tend to scratch easily, are difficult to coat or tint, and tend to create slight distortions in colors and (rarely) depth-perception.
Please visit our website www.myeyewear2go.com for more information about lenses and eyeglass types.