Do You Need Lens Coatings?

Lens coatings can enhance the performance and appearance of eyeglass lenses. If you're considering lens coatings in your next pair of eyeglasses, here's what you should know:

No eyeglass lens material — not even glass — is scratch-proof. However, a lens that is treated front and back with a clear, hard coating does become more resistant to scratching, whether it's from dropping your glasses on the floor or occasionally cleaning them with a paper towel. Kids' lenses, especially, benefit from a scratch-resistant hard coat.

With ordinary glasses, headlight glare can be a real problem. Headlight glare is diminished with anti-reflective coating applied to lenses. Photos provided by Essilor.

Today most types of plastic lenses, including high-index, polycarbonate and traditional plastic materials such as CR-39, have built-in scratch-resistant coatings. Since scratch-resistant coatings are sometimes optional, make sure your optician knows that you want them in your prescription eyeglasses.

Since a scratch-resistant coating can't completely protect your lenses from wear and tear, do keep your glasses in a cushioned case, and clean them with a microfiber cloth and the cleaning solution your optician recommends. Also, be wary of those products that promise to repair your scratched lenses. They may fill in the cracks of the scratches, but it is nearly impossible for them to make the scratches disappear so the lenses look new again.

Another lens treatment that is beneficial but invisible to the naked eye is ultraviolet (UV) protection. Just as we use sunscreen to keep the sun's UV rays from harming our skin, UV treatment in eyeglass lenses blocks those same rays from damaging our eyes. Overexposure to ultraviolet light is thought to be a cause of cataracts, retinal damage and other eye problems.

An ultraviolet treatment is simple and quick to apply to most plastic eyeglass lenses, and it does not change the appearance of the lenses at all. The exception is polycarbonate lenses, which don't need anti-UV treatment because it is an inherent property of the material.

To improve both the vision through the lenses and the appearance of the glasses, an anti-reflective coating (also called AR coating) is applied. AR coatings are similar to the coatings found on microscopes and camera lenses. They consist of several layers of metal oxides applied to the front and back lens surfaces. Because of the layering effect, AR coatings sometimes have a hint of green or purple color, depending on the individual manufacturer's formula.

Lenses without anti-reflective coating. With Crizal brand anti-reflective coating applied to the lenses. Photos provided by Essilor.

Each layer is scientifically calculated to block reflected light. The result is that you'll see a reduction in glare, annoying reflections and halos around lights. This is a great safety benefit when you're driving at night.

Also, anti-reflective coating reduces both internal and external reflections on the lenses themselves, creating a nicer cosmetic appearance. Internal reflections appear as rings that make lenses look thick. External reflections mask your eyes from a clear, complete view when someone is looking at you. So with an anti-reflective coating, eyeglass lenses appear thin or non-existent, and your eyes look more natural.

Anyone on TV or whose photo is taken often benefits tremendously from the coating, but really, all eyeglass wearers would benefit from an anti-reflective coating from a cosmetic point of view. If you have a strong prescription, you can use the AR coating in conjunction with high-index lenses to make your glasses look and feel as thin as possible.

With sunglass lenses, an AR coating is better applied only to the back surface of the lens (the surface nearest the eye). Because sunglass lenses are so dark, the AR coating can wind up looking smeary on the front surface. Coating the back side helps reduce the reflections of light that enter from behind you and bounce off the surface into your eyes. A back-side coated sun lens is much more comfortable than an uncoated sunglass.

You do have to be careful when cleaning AR-coated lenses. Use only the products that your optician recommends.
 

In contrast to anti-reflective coatings, which are very clear, mirror coatings (also called flash coatings) are bold statements of color. Just as the name implies, a mirror coating is highly reflective. The mirrored sunglasses associated with state troopers are one example of a flash coating.

The technology has advanced, however, so that today's choices include colors of the rainbow as well as silver, gold and copper metallic mirror coatings. Hot pink, blue — almost any color is available.

Mirror coatings are purely cosmetic: the wearer perceives no difference in vision regardless of what color the coating is. Only those looking at the person wearing the glasses can see the color of the mirror coating. Mirror coatings are generally applied over sunglass-dark lenses. Obviously, a highly reflective flash coating prevents others from seeing the eyes of the wearer.