Common Optical Terms

Anti-relective coating

Specialized coating to eliminate light reflections off lenses that can cause unwanted glare, especially at night. Especially useful for high index lenses or lenses that are relatively thick. This coating is considered to be revolutionary for glare management, and we are experiencing an ever increasing demand for this coating.

High Index Lenses

Lenses that are “denser” and much thinner. These are extremely appealing to those wearing strong corrections. Why? There are two aspects about lenses that correct for near and farsightedness. The lens material and the curve. The greater the curve, the greater the edge thickness, which is cosmetically displeasing to people who wear strong corrections. This is what one sees with a regular plastic lens. Glass is denser than plastic and therefore thinner with less of an edge. However, glass is very heavy and uncomfortable. In recent years, technology has seen the development for other types of plastics such as polycarbonate. This is a type of “high index” lens that is extremely light, much thinner, and with a thin edge. People with strong prescriptions find these lenses very appealing because there isn’t nearly as much cosmetic distortion as with regular lenses. Their eyes do not look artifically big or small, and their face looks more porportioned. Coupled with a feather weight frame, high index lenses have revolutioned the way people think about eyeglasses and fashion.

No-line (progressive) bifocal

Actually a type of trifocal with unique optics that allow reading and other “near” activities. There is no visible bifocal or trifocal line which is appealing cosmetically to many people. Often called a “graduated” trifocal, the power of the lens increases the farther down one looks through the lens. For example, one would look further down to focus detail at 12 inches than (s)he would looking at an item in the grocery store from the shopping cart. You can therefore choose where you want to focus.

There are many advantages to a “no-line” trifocal, especially for persons in their 50’s and older. With a “regular” line bifocal, there is only one focal point set for only one reading distance. Anything outside that focal point therefore would be blurry. Through their regular bifocal, many people have difficulty with their intermediate vision such as working at the computer, playing the piano, or hammering a nail. With a no-line, they can choose where they want to focus and can do so ofter without unwanted neck-strain. No-line trifocals however can take practice and can be a difficult adjustment for people who have worn standard bifocals for years. Also the “channel” is a little more narrow than a regular bifocal, meaning that there is not as much room in looking from right to left. However significant improvements have been made here in recent years.

Optical Center

The optical center of the lens is where maximum efficiency of vision occurs and should correspond with the optical center of your pupil. This is NOT necessarily the center of the lens, and its location will depend upon your frame, your interpupillary distance, and where the lens is to sit in front of your eye.

Pantoscopic Tilt

The angle at which your glasses sit before your eyes that allow your eyes to track upward and downward with minimal distortion.

Polarized Lenses

These lenses have become very popular in the sports world. They cut unwanted reflected glare from sunlight bouncing off water, metallic surfaces, pavement, or snow. For example, sunglasses with polarized lenses are popular and useful for fishing, driving, skiing, and other related activities. Polarization has nothing to do with UV light abosrption, but many polarized lenses are now made with a UV-blocking substance.

Scratch-resistance Coating

Specialized coating for plastic lenses that helps retard scratching or crazing of lenses. Extremely beneficial in most cases for long term preservation of quality vision through your lenses. In the last several years, we’ve seen a tremendous improvement in the chemical engineering of scratch-resistance coatings.

Transitional Lenses

Lenses that turn dark outdoors and lighten up indoors. Activation is induced by a chemical reaction to ultraviolet (UV) sunlight. Generally, they do not get as dark as sunglasses and will not darken in the car since most car windows block out UV light. Available in any lens style.

UV Tint

Not really a “tint”, but a clear chemical coating used to filter out ultraviolet light. More than a dozen studies have shown that chonic exposure to sunlight without proper protection can increase the chances of developing age-related eye diseases like cataracts and macular degeneration. We routinely recommend UV treatment of ALL glasses. It is inexpensive and offers protections against UV-A and UV-B. Also, people mistakenly believe that sunglasses automatically block out UV light by the color and darkness of the lenses. Therfore, it is important that sunglasses have UV protection as well. Usually the manufacturers’ label will indicate UV protection. Make sure the sunglasses offer complete absorption. Some labels may say “UV absorption up to 400 nm.” This is the same thing as 100% abosrption.

Vertex Distance

The distance between a corrective lens and the cornea. An important measurement with moderate to high refractive errors since the final power of a glasses lens or contact lens will depend upon its distance from the retina.