Polarized lenses...not just for boating anymore

January 15, 2009

If polled, a majority of optical eye-care professionals (ECPs) likely would report that in addition to their primary pair of eyeglasses, they also own prescription sunwear or quality plano sunwear. Patients also should enjoy the lifestyle and protection that additional sunwear provides. The percentage of prescription sunwear actually dispensed, however, is drastically lower than those worn by ECPs.

Key Points

We all know the importance of sunwear for the protection and comfort of our eyes.

If polled, a majority of optical eye-care professionals (ECPs) likely would report that in addition to their primary pair of eyeglasses, they also own prescription sunwear or quality plano sunwear.

Our patients also should enjoy the lifestyle and protection that additional sunwear provides.

The best way to increase the amount of sunwear dispensed is to have a thorough knowledge of light, the consequences of overexposure to ultraviolet radiation, and the adverse effects on the eye. In addition, a sound understanding of various sunwear technologies and their applications to vision is a must.

In optics, we deal with a very specific part of the electromagnetic spectrum-visual light. That part of the spectrum encompasses ultraviolet (UV), visible, and infrared light. The visible spectrum is found at approximately 380 to 700 nm. The color of light is determined by its wavelength, from weakest (red) to strongest (violet) and everything in between, as in the acronym ROYGBIV, which stands for red, orange, yellow, green, blue, indigo, and violet.

Ultraviolet radiation is classified as UVA, UVB, and UVC. UVA and UVB make their way to our environment, whereas UVC is blocked by the ozone layer. Overexposure to UVA and UVB are linked to premature cataracts as well as other ocular pathology. In addition, overexposure to this light energy causes uncomfortable, tired eyes and increases squinting.

As light leaves the sun and enters our atmosphere, it exhibits very specific, predictable behavior. Simultaneously, light rays refract, reflect, disperse, and diffuse. When a particular bundle of light rays enter our atmosphere at a very specific angle, the reflected light will exhibit a sort of skew phenomena and shoot off in a horizontal flash. That effect occurs when the incident angle is specific to the surface, and the surface is flat and bright (think ice on tree branches, raindrops on leaves, water, or the hood of a car). When this change of direction of light occurs, the result is extreme glare, classified as "blinding glare." Lens companies dealing with thin-film technologies continue to have discussions about the exact behaviors of light and matching the optical challenge with the correct optical solution.

The solution for glare

Glare may be defined in three categories: annoying glare, discomforting glare, and disabling or blinding glare.

It is blinding glare that occurs especially when we are driving, which gives us temporary loss of sight. We have all experienced that flash of light that shoots by our line of sight while driving. Although the flash happens for a split second, it is enough to temporarily distract us. Adding to the problem, people often can be seen driving while holding one hand up to shield the light-hardly a safe way to drive.

The optical solution is polarized lenses. Polarization manipulates the light, preventing this particular set of rays from entering the lens. Polarized lenses completely block out all light at the 180 meridian. Light still passes through 179 other meridians, and the effect cancels out blinding glare.

If I could assign a motto for polarization, it would be, "Polarized lenses-not just for boating anymore." Because most people drive cars, blinding glare can cause accidents on the road. Polarization is the only method for eliminating blinding glare, and it is available in many different colors; gray is the most popular in the United States, whereas brown is favored by our European counterparts.

Drivewear, a combination of Transitions and polarization, matches the wavelength of light energy with a changeable color that reacts to varying light behind a car windshield, on a golf course, or on the water. To enhance the effect, anti-reflective coating added to the back of lenses will eliminate back-surface reflections from entering the eye.

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