Lenses
Getting the right lenses and coating for your vision, fashion and eye protection needs is a complicated business. Fortunately for you, it's OUR business to help you select lenses and coatings that fit your prescription, budget and lifestyle. Here's a little info can help you understand your lens choices, and separate the gimmicks from the goods.
Basically, there are 5 types of materials that we make glasses with out there:
Glass CR-39 High-Index Trivex Polycarbonate
All eyeglass lenses must meet federal standards; some shops require theirs to pass even higher optical hurdles.
Glass is the cheapest and has the best optics of all the lenses, but it's heavier and, even worse, can shatter.
The future's plastic, and there are four types:
CR-39 is the standard lens used for prescriptions that aren't too strong, plus or minus 3 and lower. (CR stands for "Columbia resin," the material used for airplane windshields during World War II; 39 refers to the recipe number.) CRs usually cost about $89 to $119 for single-vision lenses, not including coatings that can add another $50 or so the total (we'll get to coatings in a minute).
High-Index: When you get into the "blind as a bat" category, higher than plus or minus 4, it's time think about trading up to high-index lenses. (How in the world do eyeglasses work, and what do all these numbers mean? Find out.)
High-index lenses are made from a denser material than CRs, so they're thinner and lighter. Not all high-index lenses are the same, though. Lenses with higher indexes of refraction (IORs) bend light more efficiently; the higher the IOR, the thinner the lenses and the steeper the price. High-index lenses cost about $70-$150 more than CRs depending on just how thin you want them.
Polycarbonate is the lens of choice for kids and athletes because it's the most impact-resistant (it's the same stuff used in bulletproof glass) and also has a high IOR, but not the best visual properties (???? Go figure – we put kids in a lenses that’s safe but has the worst optics of all materials??). State law requires us to sell ***ONLY*** polycarbonate to kids under 18.
A tip: Because the material is so flexible and soft, it is therefore highly scratchable; no coatings will really help reduce that issue. You can skip the UV protective coating too, since the material has built-in ultra-violet protection. With these lightweight, slim lenses, which are priced in the same ballpark as high-indexes, you're primarily paying for the extra durability.
The downside of polys is that they have a lot more distortion than other thin lens options. So unless you spend more time on the basketball court than in your car, go with high index.
Another term you'll hear is aspheric lenses. These are also thinner than your garden variety (called non-aspheric), but this slimming down is done by the manufacturing process rather than through the lense's composition. Most high-indexes and polys are aspherics; and from what I can tell these lenses aren't any more expensive than chunkier versions. CR-39s aren't ground into aspherics because it would alter the optics making it a visually compromised lens.
One of the primary reasons to ask for the aspheric lenses is because of their cosmetic properties and visual attributes. Besides being thinner by nature, they won't magnify your eyes as much or make it look so small.
The Artful Eye Optical Emporium
265 East Main St.
East Hampstead, NH (map)
603-382-1195
More information on lens types and options (rollover for definitions, click for more information):
Single vision
Bifocal
Trifocal
Progressive
Transitions Progressive
Polarized
Drivewear
Plastic
Glass
Trivex
Polycarbonate
High-impact lenses for professionals who require MIL-PRF-31013 or ANSI Z87.1-2003 High Velocity Standard protection
Lenses with special curvature to reduce weight and edge thickness
Anti-reflective coatings
