ask the labs
Oldies But Goodies
Karlen McLean, ABOC, NCLC
The following items are from the archives of "Ask the Labs" columns written by EB's late lens guru, Joseph L. Bruneni. After a little updating, the information answers questions still asked of labs today.
WHERE DOES UV END? (1999)
Q Several brands of lenses advertise 99 to 100 percent UV blocking at 380nm. But if UV extends all the way to 400nm, is there valid concern about the UV range between 380nm and 400nm?
A There is a common misconception that UV radiation extends to 400nm. In fact, all U.S. and ISO standards define UV as the waveband from 315nm to 380nm.
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. ANSI Z80.3 uses that data to provide recommendations for UV protection.
For radiation at wavelengths longer than 380nm, there is no requirement for protection from solar radiation. This would include blue light hazard, visible light, and infrared radiation. It was found that with the solar intensity and energy necessary to produce damage, there was 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 a number of different tasks.
MONOCULAR PD, HIGH-INDEX (2001)
Q It's recommended that monocular pupillary distance be taken when dispensing poly. Is this also the case with high-index materials?
A Any lens material with a lower Abbe value than glass or CR39 benefits from monocular PDs.
In addition, many people ordering high-index lenses tend to have strong corrections, and most patients don't have perfectly centered noses, so monocular PDs are always advisable for proper fitting of high-index lenses (and poly).
Take monocular PDs on everyone. Tell patients why accurate measurements are important, and how your instruments contribute to the accuracy of the final eyewear. EB
TRIVEX TIPS (2003)Q Are there hard numbers about the impact resistance of Trivex compared to poly? What is Trivex's Abbe value and can it be scratch resistant and AR coated?A Multiple industry sources have found that the strength of poly is consistent. PPG, the producer of Trivex, and two of the manufacturers using Trivex claim it is comparable to poly. The best indication of this is that the Z87 standard accepts Trivex as poly's equivalent. Each lens manufacturer has made slight modifications to its Trivex resin so the specs vary between brands. Trivex lenses have an Abbe value ranging from 43 to 46 depending on the manufacturer. Trivex lenses come with a durable front-side hard coat, and they're more scratch resistant than many plastic lens materials regularly dispensed without a backside coating. However, for maximum scratch resistance, a backside coating may be applied. AR works well on Trivex lenses, and Trivex lenses can be tinted easily. The unique molecular structure of Trivex provides a jewel-like appearance to edges that are rolled and polished. |
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Email: karlen.mclean@wolterskluwer.com. Facebook: Facebook.com/Eyecarebusiness. An archive of past Ask the Labs columns can be found on the Eyecare Business website: EyecareBusiness.com.
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