When selecting eyeglass lenses, it is helpful to understand the many choices available to you. Options fall into three categories:

· Lens materials (what the lenses are made from)

· Lens designs (how the vision correction is "designed" into the lens)

· Optional lens treatments such as Anti-Reflective Coating and Polarization.

Lens Materials

The development of new lens materials has vastly improved the look, the feel, and the comfort of today's eyeglasses. The following information will give you a good idea of the what materials are available, along with their respective benefits and drawbacks.

Plastic lenses (also known as "hard resin")

· Developed about 1950; made of a hard resin called CR-39

· UV Coating

· Can be coated with a scratch-resistant coating to help protect against everyday scratches

High-index lenses

· Newest type of prescription eyeglass lenses

· Work for high prescriptions

· Lighter in weight and thinner at the edge than regular glass or plastic lenses

· Feel more comfortable and look more attractive than regular plastic or glass

· Available in both glass and plastic, with plastic being more popular

· Scratch-resistant and anti-reflection coatings are often recommended for these lenses

Polycarbonate lenses

· Originally developed by the aerospace industry for use in the face shields of Apollo astronauts

· Introduced in 1980; a type of high-index lens

· Lightweight and extremely thin like other high-index lenses

· Made of a plastic used for bulletproof windows; four to five times as impact resistant as any other lens and ten times more impact resistant than other plastics

· Required for children under 12 years of age.

· Recommended for children's eyewear and for sports

Note: Even though polycarbonate lenses are impact resistant, they are not shatterproof. Today's eyeglass lenses must meet federal impact-resistant standards. But they can break, depending on the size and the speed of the object striking them. For eye-hazardous jobs or sports, non-prescription safety eyewear that meets American National Standards Institute (ANSI Z87.1 standard) can be purchased from optometrists or hardware and sporting goods stores. Optometrists can also provide prescription safety eyewear that meets the ANSI standard.

Photochromic lenses

· Photosensitive lenses that change from clear to a comfortable tint when you go outdoors

· Available in plastic or High Index.

Aspheric lenses
Aspheric lenses are flatter to look slimmer in frames. They also make eyes look more natural in size. If you're very nearsighted, your eyes will appear to "shrink" less. If you're very farsighted, eyes will look less magnified. Aspheric lenses are available in single-vision, bifocal, and progressive styles.

Lens Designs

Single-vision lenses
If you are only nearsighted, farsighted, or need help with reading, your eye care professional will prescribe "single-vision" eyeglass lenses. This means there is only one correction power throughout the entire surface of each lens.

Multifocal lenses
There are three types of multifocal lenses:

· Bifocals are lenses which offer two prescriptions in one pair of eyeglasses-one for near vision at the bottom and one for distance vision at the top. This arrangement can be altered to meet occupational needs. In a standard bifocal, a line between the lens prescriptions is visible, and there is no correction for mid-range viewing. Blended bifocals eliminate the line, but have a blurred zone between the lens prescriptions.

· Trifocals are lenses which offer three lens prescriptions in one pair of eyeglasses. They correct near, mid-range and distance vision. The usual arrangement is distance vision on top, mid-range in the middle, and near vision on the bottom. This arrangement can be altered to meet occupational needs. Wide-band trifocals, for example, have a wide mid-range designed for wear when using a computer. With standard trifocal lenses, the lines between the lens prescriptions are visible.

· Progressive "no-line" lenses are lenses which provide a gradual, invisible change in lens power from bottom to top. This allows the eyes to move more naturally as you view near, mid-range, and distance objects through the lens-and eliminates the use of aging prescription segment lines.

Special Treatments

Scratch protection
Scratches look unattractive and can affect the optical quality of your lenses. Scratch protection is a surface coating that is applied to plastic and polycarbonate lenses, which scratch easily. The coating protects lenses from scratches caused by everyday use.

Ultraviolet (UV) protection
UV protection is a tint or surface coating that blocks and protects eyes from the hazardous ultraviolet rays of the sun. Polycarbonate and most other high-index lenses have built-in UV protection.

Anti-reflection coating
An anti-reflection coating is a single- or multi-layered surface coating applied to either glass or plastic lenses. Its purpose is to virtually eliminate distracting reflections from your eyeglasses. There are two major advantages to applying an anti-reflection coating. First it enhances your appearance by reducing reflections on the lenses that hide or distort your eyes. Second, it improves vision by letting more light reach the eye. This is very beneficial for dusk or night driving because it decreases the glare from headlights and streetlights. Anti-reflection coatings also combat indoor glare and are often recommended for public speakers, television personalities, and anyone in the public eye.

Polarization
Polarized lenses eliminate horizontal glare. The eyes relax more and enhance vision on bright or cloudy days. Polarized lenses include 100% UV radiation protection.