Spectacle Lenses

You probably have a pretty good idea of what kind of frames you want. But the most important part of the eyewear, the lenses, is largely a mystery for most of us. Your professional optician will guide you expertly through the many choices available, so you get the lenses best suited for you prescription and lifestyle. This list is a brief overview of the major types of lens options you will want to discuss with your optician.

Lens Materials

Hard Resin (plastic)

Conventional hard resin lenses are half the weight of glass lenses and can be tinted to almost any color and density. Hard resin lenses are more easily scratched than glass but can have an optional scratch protection applied. More impact resistant than glass, hard resin lenses do not require heat treating.

Lighter,Thinner Lenses

Modern technology has created lenses that bend light differently so that stronger corrections are thinner than when made in conventional materials. Such lenses are called "high index" and stronger corrections are more attractive because they are thinner. Glass lenses are also available with the slimming advantages of high index but are considerably heavier. High index plastic uses less material so the lenses are often lighter in weight. High index lenses absorb all harmful UV light and can be tinted to any shade or color.

Lenses that Darken in the Sun

These photochromic lenses darken as you go from indoors to outdoors. They are available in both glass and lightweight hard resin. They darken to a moderate shade of grey. A demonstration of these lenses is the best way to learn about their properties.

Polycarbonate

This is the most impact resistant lens material available and are always the lens of choice for young people and other active clients. Polycarbonate lenses are high index and are usually the lightest, most comfortable lenses. They absorb all harmful UV light and can be made with ultra thin edges because of their unique strength.

Glass

For years, glass was the only lens material available and glass still offers superior optics. The most scratch-resistant material, the primary disadvantage of glass is its weight, generally twice that of hard resin. Glass lenses are heat or chemically treated to increase impact resistance.

Lens Designs

Single vision lenses

Single vision lenses function as all purpose glasses for persons who have normal accommodation. Persons who normally wear bifocals or trifocals can use single vision for distance or near lenses. Single vision lenses can also function as occupational glasses for certain types of work. Single vision lenses are available in all lens materials.

Aspheric lenses

These lenses provide special visual and cosmetic benefits for stronger corrections and increase edge to edge clarity. Flatter than conventional lenses, aspherics eliminate the "bulgy" appearance of strong plus lenses and greatly enhance the appearance of finished eyewear. Persons with strong nearsighted corrections also benefit from thinner, lighter weight glasses when their lenses are aspheric. Because aspheric lenses are positioned closer to the face, there is less eye magnification with farsighted corrections and less of the "small eyes" look with nearsighted corrections. Aspheric lenses are often made of high index materials for the ultimate in thin lenses.

Flat-top bifocals:

This is the most popular bifocal format and is available with the bifocal portion made in a variety of widths to help with various close-up occupations. Flat-top bifocals are made in every type of lens material.

Franklin Style Bifocals:

Sometimes used for those who need a wide field of vision for near work (accountants, for example), Franklin style bifocals have a distinctive appearance and are thicker because of their design. They are generally only available in glass, hard resin and photochromic glass. They are being replaced by wide flat-top bifocals.

Trifocals

Trifocals come in a variety of designs. Flat-top trifocals are the most widely used form. The added segment provides clear vision at arm's length distance, the area that is usually blurred for bifocal wearers. Trifocals are available in all lens materials.

Progressives (no line bifocals)

These lenses provide all the benefits of bifocals but add the feature of continuous clear vision at all distances, including mid-range distance (arm's length). Progressives have the cosmetic advantage of appearing to be single vision lenses so they never reveal that the wearer is using bifocals. Progressives are available in all lens materials and also made in aspheric form. Because of their many benefits, they are becoming the lens of choice for bifocal and trifocal wearers.

Occupational Requirements

Many occupations impose demanding visual requirements on those who wear bifocals or trifocals. In addition to safety concerns, be sure to discuss the wearer's job tasks so the lenses can be designed for specific requirements.

Sports Glasses

All sorts of special lens designs are available for the needs of sports enthusiasts. Polycarbonate is the material of choice for active sports. (See the August 1996 Opticianry Today for an overview of visual requirements for selected sports activities.) Polarized sun lenses that eliminate reflected glare are especially appropriate for drivers, fishermen, hunters and all types of outdoors activities.

Computer Glasses

There are a variety of options for those who use computers. These include special filters and anti-reflection coatings.

Optional Lens Treatments

Scratch Protection Coating

Light weight hard resin lenses can be more easily scratched than glass lenses. Special coatings have been developed to help protect lenses from normal scratching. The modest additional cost for such scratch coating is a prudent investment.

UV Protection

It is generally accepted that the ultraviolet rays in sunlight pose potential harm to the eyes. Special treatment for hard resin lenses completely blocks hazardous UV light. Lenses like Polycarbonate and high index include built-in UV protection.

Anti-reflection Coatings

Special anti-reflective coatings, much like those used for fine camera lenses, are available for spectacle lenses. These coatings are particularly effective for reducing eye fatigue for computer operators and anyone driving at night. And, of course, AR lenses enhance appearance by removing all distracting reflections. After you have discussed the ways in which you will be using the new glasses, you can choose the exact combination to effect the "magical" result of better vision and eye protection.