Michael D Wesson, OD, MS, FAAO
FAMILY VISION CARE

Sunglasses have been available for many years. Contrary to standard sunglasses that are constructed by dipping lenses in special dyes to obtain the color and density (darkness) wanted, polarized lenses are layered by having a very thin film of material sandwiched between clear material such as plastic, polycarbonate or glass. This thin film has a special property called polarization that dramatically reduces light scatter inherent in all regular light sources such as sunlight. When sunlight is reflected off any shiny surface such as water, snow, and auto surfaces, light rays are scattered in all directions. Light entering the eye in these many directions create what we refer to “glare”, a very uncomfortable condition that can cause headaches, tearing, and sunlight aversion.

Testing Polaroid Glasses

The polarized film limits the direction that light can pass through the film by letting light enter the eye from one specific orientation, usually vertical. This eliminates most of the glare. The quality of the polarized material plays a part in the efficiency of the selective orientation. How can you tell if the material is acceptable quality? It’s easy. Pick up two identical Polaroid sunglasses and look through one lens while rotating another lens in front of the first lens. There should be a point where no light passes through the lens combination. Perfect cancellation suggests acceptable quality. Also the film should be oriented so that the two lenses are at right angles to each other with one pair of glasses straight across as if the glasses are being worn. That’s it!

Advantages and Disadvantages

Are there other advantages of wearing polarized lenses other than glare elimination or reduction? Indirectly it should eliminate headaches if caused by glare. In addition the ability to see in water is greatly enhanced and the ability to see objects more clearly is also improved. In both cases this is because only rays of light with one orientation are being seen and this improves object contrast.
There are also disadvantages with Polaroid lenses. One major problem happened to me. I had installed a flow meter on my boat to measure gallons used at different engine speeds. It was a difficult installation and a friend of mine and I went out for the maiden run. I had him record the fuel usage as I changed speeds. It seemed to work fine but when I looked at the gage I could not see it clearly (interesting for an eye doctor). When the run was finally completed we headed back in and I took my Polaroid sunglasses off. Boy- was I surprised. The gage was crystal clear! I had experienced the effect of polarization on “liquid crystal displays”. This type of display is found in automobile dashboards, airplane gages and boats. I examined a patient who complained that she could not see her reflected gages. She brought the car back to the dealer several times before she realized her polarized lenses were blocking her vision.

Does Lens Thickness Matter?

Finally there is some mention in the literature about different thicknesses of non- prescription Polaroid glasses. I did some in–house research on different brands of Polaroid sunglasses with the help of my assistant and one of our Opticians. We examined 9 different brands and found that although they all worked well as sunglasses, there was definite differences in thickness. Four brands had a thickness of 2.0 mm. One of the brands was glass and the other three were polycarbonate. The other five brands were all plastic lenses with thicknesses varying from 1.0 mm to as little as 0.06 mm. I suggest that when you purchase sunglasses consider buying those that are polycarbonate. The major advantage of these thicker sunglasses is eye safety and has nothing to do with their polarization.
In conclusion, Polaroid sunglasses are far more rewarding than regular sunglasses.