While geek chic glasses are no longer so geeky, there’s still a stigma surrounding the vintage poindexter look, characterized by thick, Coke-bottle glasses. If you’re looking for thinner, more stylish lenses, optometrists offer hi index lenses in a variety of thicknesses. Here’s what to know before deciding whether or not to buy hi index lenses, also written as high index lenses.
What Are Hi Index Lenses?
Hi index simply refers to a pair of glasses’ index of refraction, or how much the material bends light that passes through it. A higher index means the lenses are better at bending light, so they don’t need to be as thick. Plastic lenses have an index of 1.50 and glass has one of 1.52. Any lens with an index higher than that is considered hi index.
Three common grades of hi index lenses are:
1. Polycarbonate lenses have an index of 1.59 and are 25 percent thinner than plastic lenses. They’re also the most economical type of lens in the category.
2. 1.67 hi index lenses, which are 40 percent thinner than their plastic counterparts.
3. 1.74 hi index lenses cost a pretty penny. They’re 50 percent thinner than plastic but they’re harder to find and typically recommended for people with very strong prescriptions.
The Benefits of Hi Index Lenses
1. Because hi index lenses require less lens material they are lighter and more comfortable than regular glasses with the same prescription. A lens of this sort makes the biggest difference for patients with prescriptions of +/- 3.00 D or more.
2. If you’re interested in drilled, rimless glasses, hi index lenses produce a much sleeker look and don’t stick out from the frames as much.
3. Most hi index lenses have an aspheric design. This reduces the bug-eyed look produced by strong, farsighted glasses and the “reverse telescope” look that occurs with nearsighted prescriptions.