Q. How Clear is Clear?
I am a dispensing optician with Kaiser Permanente So. California. In the past I have read articles referring to a new process using the term "water white," which leaves the polycarbonate lenses crystal clear. In addition to its distinctive sound, the blue hue was always an identifier of the material, which I found a blessing and a curse. One of our lab people and I were discussing polycarbonate yesterday. Our views were a little different, especially on the term "water white." His position was that this was just hype and no such product exists. I believe that it does. Could you enlighten me on this subject? Also, who manufactures the raw product used to make polycarbonate lenses?--Margie K. Melby, ABOC, El Cajon, Calif.

A.
I'm pleased to tell you that "water white" polycarbonate is real, not an ad writer's dream. The slight blue color is inherent in the poly resin, which comes to lens manufacturers in the form of pellets (similar to large grains of sand). About one year ago, one resin supplier found a way to manufacture poly with no color. The term "water white" was coined to describe the new poly. It's considered a purer, higher quality of poly.

The new resin is available from both Bayer and GE Plastics (the two primary suppliers of poly resins). Obviously, lens manufacturers couldn't switch 100 percent to water white, since it would result in mixed inventories. Lens manufacturers are using water white primarily for new poly products. For example, Vision-Ease's Tegra line is water white, since the entire Tegra line is new. Most poly manufacturers either include water white in portions of their line or will soon have it. The slight blue color was an advantage, but poly can still be recognized by a slight "rainbow" look to the lens coating. Try examining a poly and non-poly lens side by side. Hold them under overhead fluorescent lights and you should see slightly more color in reflections from the surface of the poly lens.

Q. Where Does UV End?
We have noticed several brands of lenses advertised as offering 99-100 percent UV blocking, but when we check their specs, they show the lenses block 100 percent of UV at 380nm. We're concerned because UV extends all the way to 400nm. Is there valid concern about the UV range between 380 and 400?

A.
There is a very common misconception that UV radiation extends to 400 nanometers. In fact, all U.S. and ISO standards define UVA as the waveband from 315nm to 380nm. These standards include ANSI Z80.1 - Prescription Ophthalmic Lens Recommendations, ANSI Z80.3 - Nonprescription Sunglasses and Fashion Eyewear Requirements, ANSI Z87.1 - Occupational and Educational Eye and Face Protection, and equivalent ISO (international) standards for Rx and plano lenses.

Studies have considered the intensity of radiation at different wavelengths, the absorption of tissue to radiation, and the amount of energy necessary to produce damage. Based on these considerations, ANSI Z80.3 provides recommendations for UV protection. For radiation at wavelengths longer than 380nm, there is no requirement for protection from solar radiation. This would include the blue light hazard, visible light, and infrared radiation. It was found that with the solar intensity and energy necessary to produce damage, there was simply no need for radiation attenuation. In an industrial setting, there can be exposure to radiation that requires attenuation of UV, blue light, visible light, or infrared radiation. ANSI Z87.1 provides specific guidance for attenuation for a number of different tasks.

The OLA's book Spectral Transmittance of Lens Materials is a good source of information on the transmittance of UV, visible, and infrared radiation.--Dan Torgersen, OLA Technical Director

Q. An Optical Oxymoron
What is a single vision progressive lens? I read about it, but the name seems to be a conflict of terms.

A.
Your confusion could be a result of the author's published material. The term was coined to describe a relatively new category of variable focus lens for use at near and mid-range focal lengths.

Three manufacturers produce such a lens. The first was Readable� by Varilux. Sola's is called Access, and Shamir has the newest version called Office�. A better term for these useful lenses might be "variable focus near vision lens." They are prescribed for the patient's reading correction. The add power gradually weakens toward the top of the lens. This makes a superb occupational lens for computer users. The weaker add power toward the top of the lens provides clear vision at arm's length where most computer monitors are positioned. The lenses are available in two versions, usually 0.75D and 1.25D, the number indicating the amount of add reduction in the top portion of the lens.

A common name for this type of lens is necessary. Sola calls Access an "enhanced near vision lens." Shamir calls its a "computer lens." A better generic term might be "variable focus reading lens." Whatever you call them, they should without question be one of the lenses you offer your presbyopic patients. These marvelous lenses are particularly useful for computer users, but should not be limited to that use. EB

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