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Your monthly guide to staff training outside the box
Eyes / Lenses / Fitting Lenses / Free-Form / Frames / Sunwear / Patient Solutions / In-office / Standards
SUNWEAR, Polarized
THE PHYSICS OF POLARIZING LENSES
By Ari Siletz
Sunlight can become partially polarized by the scattering of air molecules or by reflecting off something like a lake. This means that after scattering or reflecting the sun's waves oscillation angles, they are no longer random in all directions but have a preferred direction on average. In the case of a horizontal surface—like a lake or a road—the preferred direction is horizontal. This horizontally vibrating reflected sunlight is the nuisance we see as glare, and this is why polarized lenses are so useful to beachgoers and motorists: They block glare. The polarized filters on these lenses preferentially block the horizontal component of light oscillation while transmitting the vertical component. The result is a darker image but with better contrast.
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POLARIZING TECHNOLOGY
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Crystals in the film embedded in polarized lenses are arranged to create a vertical polarizing filter that absorbs the blinding horizontal rays letting only the useful light through. Polarized lenses improve contrast and enhance the visibility of all colors. Available in 1.67 high-index, polycarbonate, Trivex and plastic, polarization can deliver the right thinness, lightness and properties personalized for each wearer. Polarized lenses provide 100 percent protection from harmful UVA and UVB rays.
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POLARIZED LENSES
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Only polarized lenses filter the intense reflections of light that become polarized and intensified when bouncing off flat surfaces. A specially oriented polarizing film encapsulated within the lens selectively blocks the horizontal waves of reflected glare.
With ordinary sunglasses, any blinding flash from reflected
surfaces would be reduced in brightness but still transmitted through the lens and into the eye.
Since the liquid crystal screens (LCD) on cell phones, PDAs,
car dashboards and gas pumps are also polarized (at 45 degrees), the 180-degree orientation of polarized lenses may block some of the screen—that's normal. Be sure to advise patients and suggest tilting their head or the cell phone 45 degrees for greater visibility.
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COMMUNICATING
POLARIZED LENS OPPORTUNITIES
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To start an outdoor eyewear discussion, try these talking points:
- "Polarized lenses make the best outdoor eyewear. They eliminate glare, especially reflections off the road and from car windshields, enhance contrast for sharper vision, and their polarizing crystals make vision the most comfortable for all-day wear. If you cycle, fish or boat, you know they're a must. For golf, it's personal preference but if you fly a plane, since the new instruments are LCD and also polarized, they can hide the numbers and scales on the gauges so they're not recommended. Do you have any questions?"
- "The different colors of outdoor lenses filter light in different ways, and that's an important choice. Colors should be chosen by activity and sport, and customers have preferences for color and density (darkness of lenses) by age."
- "We always add no-glare AR to the backs of polarized sun lenses. The AR eliminates reflections of objects behind you (even reflections of your eyes), which appear very big and bright. Adding no-glare makes for the best vision in polarized sunwear. Have I made the explanation clear?"
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UV/HEV ATTENUATING
Lens treatments like photochromics and polarization, or combinations of the two (Transitions Drivewear, NikeMax Transitions, others) are 100 percent UV-absorptive. For blue light, lenses with color treatments provide selective absorption using either polarizing films or tints. Some sun lenses are specifically designed to filter or selectively absorb more of the HEV than others (Vision-Ease Coppertone gray and brown, Oakley VR28 Black Iridium Polarized, others). Therefore, knowing the transmission characteristics of lenses before and after coating allows you to deliver the best outdoor lenses that block UV and HEV. Request transmission curve charts from your lab or lens manufacturers (total lens = lens material + coating and/or treatment) to know the best lenses to attenuate short wavelength, high-energy blue light outdoors. Also ask for the lab's recommendations.
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GLARE CONTROL
Glare knows no season so recommend glare protective eyewear to all patients all year-round. Quality sunwear or outdoor eyewear protects patients from the more troublesome types of glare, from the annoying that makes one squint or put a hand up to the disabling that causes you to close your eyes or turn away. While medium to dark tints and photochromics can help with these, only polarized lenses can eliminate blinding glare by absorbing sunlight reflecting horizontally off water, glass, snow or sand. Light is horizontally reflected when it hits flat surfaces.
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RAYLEIGH'S EFFECT
The sun's blue and violet wavelengths of light entering the earth's atmosphere are scattered causing haze as they cross over each other. This is called Rayleigh's Effect.
Polarized lenses absorb horizontal scatter so they reduce the effect of haze, and objects appear sharper and clearer. Absorbing the haze and scatter is in part what makes quality polarized lenses so comfortable to wear. Tell every patient that polarized lenses are the most comfortable outdoor lenses to wear. Now let me tell you about the colors...
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POLAR WEATHER? POLARIZE
Because glare—not necessarily bright light—is the biggest issue in wintertime, polarized sunglasses are an excellent choice to alleviate eyestrain while also shielding the eyes from damaging UV radiation. The enhancing effect that polarized lenses have can also serve to "brighten up" those dull winter days. Be sure to warn patients interested in engaging in certain winter sport activities that polarized lenses may not be right for them—several skiers, for example, advise against polarized lenses because they may inhibit the ability to identify patches of ice by seeing the unique glare they cause. For those patients who prefer (or require) tinted lenses over polarized, suggest Trivex material lenses as an alternative, as they're more conducive to dyeing, while offering the same safety features (and will prove to be more lightweight, a special consideration for those patients who may choose larger frames).
—Preston Fassel
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