EYEWEAR INFORMATION
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There are many different lens designs and materials available today. Lenses can now be tailored to meet the needs of the individual.
Lens designs
Single Vision – This is a design which has one prescription in the lens correction for nearsighted, farsighted, or astigmatism.
Bifocal – This is a design which allows vision through the top portion for distance tasks and the bottom portion for near tasks.
Trifocal – This is a design which allows vision thouugh the top portion for distance tasks, the middle portion for intermediate tasks, and the bottom portion for near tasks.
Progressive addition (no-line) – This is a lens design which is similar to a trifocal allowing vision for all ranges. However, since it is designed without lines, the lens progresses in power in the bottom portion of the lens to allow for the various ranges of near tasks.
Lens Materials
Glass – This old standard is now virtually obsolete. It is the heaviest and least impact resistant of all materials. However, it is very scratch resistant.
Plastic – This is a material which is significantly lighter than glass as
well as being inherently impact resistant.
Hi Index – This is a form of plastic which is even lighter than standard plastic lenses. Lenses are graded by the term index of refraction. This means how the speed of light passing through a lens compares to the speed of light passing through the air. The index of refraction of air is 1. The higher the index, the slower the light passes through. Therefore, the higher the index, the thinner the product will be, all other factors being equal. Lenses are available in 1.54, 1.60, 1.66, 1.67, and 1.71 indexes.
Abbe Value – Abbe value is the determination of the amount of color aberration, caused by the material. Color dispersion results from uneven bending of the different wavelengths of white light, it is often described by the patients as a halo in the periphery. The vision through the optical center is crisp but as the eye rotates, the patient might feel the effect. The higher the Abbe number, the less the color dispersion.
Polycarbonate – This is a lightweight lens which is the most impact resistant of the materials today. It was originally used for safety lenses, but has been improved and is now also used for dress eyewear. It has the most distortion and a low Abbe value.
Anti-Relective Coating – This coating is designed to reduce reflected glare to the eye from viewed surfaces, enhancing cosmetic and visual off of the lenses. With anti-reflective coating, this can be reduced to only .5% loss. This greatly aids night driving and computer use by reducing the reflected glare off of the lenses.
Transition, Sunsensor, and Colormatic – These lenses change color form a light grey or brown indoors to a darker gray or brown outdoors.
Polarized Sun Lenses – These offer unique protection from the sun. Not only do they block out harmful ultraviolet light rays, they also cut out horizontal glare. This results in very comfortable vision. They are great for driving. They are also terrific for any type of water activity, as they remove the glare from the water which allows you to see into the water.
Transition Next Generation
These lenses change color 7 times faster and lighten 4 times faster than the previous Transition lenses. They also get lighter inside and darker outside than the previous ones. Although they do not replace sunglasses, they do make a very comfortable lens to wear. They are available in gray and brown.
