|Polarized lenses eliminate blinding glare (ImageWear’s Callaway Force shown here).|
|Mirror coatings provide a host of optical benefits as well as adding a fashion element (adidas’ Sydney shown here).|
|Sunglasses offer protection from UV radiation and should be worn by children as early in life as possible (Polaroid Kids’ Sun Style No. PO411S from Safilo shown here).|
|PHOTOCHROMIC MEDICAL FILTERS Medical filter photochromic lenses are designed to improve contrast, comfort, and adaptation time when light levels change and are for light sensitive people. They eliminate virtually all blue light and ultra-violet radiation. Patients should be confident they can distinguish the colors in traffic signals before driving as these filters don’t pass some ANSI traffic signal requirements. In addition, the lenses shouldn’t be worn for night driving.
The photochromic medical filter eyeglass lenses with low, medium, or high blue light filter cutoffs are:
• lemon yellow (450 nanometers)
The more knowledgeable you are about sun lenses the better you can help your patients get the protection they need.
Rather than being sold as a second pair, ECPs would be well advised to tout sunglasses as the other first pair of eyewear patients should own. The following questions will test your knowledge of some of the science behind today’s sun lenses so you can help educate your patients about the benefits of wearing them.
1. Polarized lenses are recommended as the best solution for the elimination for which type of glare?
The correct answer is d. blinding glare. This type of glare occurs when light reflects off shiny surfaces or scatters in the sky. Polarized lenses are the best option because they are specifically designed to eliminate this type of bright, reflected glare.
There are three other forms of glare. Distracting glare occurs as light reflects off lens surfaces and is reduced or eliminated with an anti-reflective (AR) treatment on a lens, which may be applied to clear, fixed tint, or photochromic lenses. Discomforting glare happens as light levels change; photochromic lenses are best suited to counter it. Disabling glare ensues when light is too bright; fixed tint, photochromic, and polarized lenses are all good recommendations for this kind of glare.
2. Which kind of mirror coating reflects light without absorbing any light?
The correct answer is a. dielectric. This is a process that creates a mirror which reflects light without absorption. It takes a minimum of five layers to create a dielectric mirror, although most designs employ 20 or more. A dielectric mirror treatment produces fun, brilliant, and funky colors. Metallized coatings absorb light and reduce visible light by 25% to 35%. They are a solid, reflective one-way mirror effect that usually comes in gold, silver, or blue. Flash mirror coatings have just a hint of mirror on the lens. Flash mirror treatments reduce visible light by approximately 8% to 12%. Most premium mirror coatings have a layer over the mirror surface to protect it during cleaning and from minor scuffs and scraps. A hydrophobic topcoat wards off liquids and oils, which keeps the surface cleaner longer as well as making it easier to clean. A gradient mirror is great for reducing bright overhead light.
3. Which tint color would you recommend to help eliminate haze on a cloudy day?
The correct answer is d. yellow. These lenses filter out blue light, making them an excellent choice on hazy and overcast days. Yellow lenses are often used by hunters and shooters. Blue is good for tennis players, golfers, or snowmobilers. Brown lenses are more popular in Europe. It is often used by golfers or skiers, particularly on overcast days because brown lenses offer improved contrast.
Gray lenses are preferred by almost two-thirds of sun lens wearers. Gray transmits colors evenly, meaning the colors are true. These lenses are great for general purpose sunglasses. Green is the color that is most soothing to the eye. The G-15 lens is probably the most recognized lens by sunglass wearers. It is a great lens color for tennis players and drivers.
4. How much more UV radiation does the average child receive compared to an adult?
a. two times
b. three times
c. four times
d. five times
The correct answer is b. three times. The annual UV exposure for the average child is three times that of an adult. That’s because the crystalline lens of the child transmits approximately 7 Â½ times the amount of harmful UV radiation as does the yellowed lens of an adult. Studies have shown the bulk (80%) of lifetime UV radiation exposure occurs prior to age 18. Exposure to UV radiation is cumulative and has been linked to increased risks of brown cataracts (sunshine), lid and skin cancers around the eyes, photokeratitis, pingueculaes, and pterygiums. Sunglasses offer protection from UV radiation and should be worn by children as early in life as possible.
5. When looking at the electromagnetic spectrum, which classification of radiation is responsible for “œheating?”
d. visible light
The correct answer is b. infrared. Unlike UV energy that causes photochemical affects in the eye, infrared radiation transforms into heat. This heat raises the temperature of the internal structures of the eye and denatures tissue. Since infrared energy is much lower than visible or UV energy, it takes high amounts of infrared or repeated lower exposures to create eye damage. The tissues in the eye that are most vulnerable are the cornea and the aqueous humor, although all other tissues can be affected. Cataract formation has long been associated with certain occupations connected with high infrared exposure, like glass workers.
Studies suggest that blue light (HEV) may also contribute to retinal damage and possibly lead to macular degeneration. The retina can be harmed by high-energy visible radiation of blue/violet light that penetrates the macular pigment found in the eye.
Ultra-violet C (UVC) radiation is filtered by the ozone layer so that none reaches the earth’s surface.
6. Which of following lens colors would be best to recommend for someone playing golf?
The correct answer is a. copper. Copper, brown, or dark amber will all block high amounts of blue light. They also increase contrast and visual acuity. These lens colors are useful to improve contrast on grass and against blue skies. They’re also a good choice for tennis players.
Rose or red lenses help increase contrast when worn in partly cloudy and sunny conditions, but this color lens causes significant color imbalances that some patients may find unappealing.
Yellow or orange lenses eliminate blue wavelengths of light that heighten contrast in overcast, hazy, low-light conditions.
7. Which optical phenomenon is responsible for making mirror treatments work?
a. constructive interference
b. destructive interference
c. selective filtering
d. variable filtering
The correct answer is a. constructive filter. A mirror treatment is made using the same equipment used to produce AR treatments but the thickness of the coating is one-half the wavelength of the light instead of one-quarter of the wavelength used for AR treatments. This thickness makes light wave enhance each other, causing the mirror effect. With AR treatment, the waves destructively interfere with each other.
8. How can you determine the absorption and transmission properties of a sun lens?
a. ask the manufacturer
b. use an office photo meter (like your UV meter)
c. review the lens’ spectral transmission chart
d. look for the information on the Internet
The correct answer is c. review the lens’ spectral transmission chart. These tables illustrate the performance of any lens, including sun lenses. They are produced by testing the lens wavelength by wavelength and the results recorded, then displayed as a graphic illustration.
Because sun lenses offer terrific benefits for patients, be sure to keep up with their technical merits so you can recommend the best options for your patients.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.