OpenOptix ABO Study Guide - Laramy-K Optical

demonstrated by taking a pair of polarized sunglasses outside on a sunny day. Find a
reflection of sunlight on the hood or windshield of a car. Hold the sunglasses in front of
your eyes and view the reflected sunlight through the polarized lenses. Notice the
intensity of the reflection drop dramatically. Now rotate the sunglasses 90°, just as if
you were to tilt your head to one side or the other, and notice the intensity of the
reflection return illustrating how the horizontal alignment of the polarizing filter interacts
with the reflected polarized light. This horizontal alignment makes correct placement of
the polarized lenses in the wearer's frames imperative.
Polarizing filters are created by stretching sheets of polyvinyl alcohol (PVA) so its
molecules align in long directional chains. The PVA is then passed through an iodine
solution where the light absorbing iodine molecules attach to the molecular chains
forming the microscopic blinds. The film is then incorporated into the lens blank as it is
poured, creating polarized lenses.
Tinted vs. Polarized
Although tinted sunglasses may reduce brightness and improve wearer comfort, they do
not remove glare like a polarized lens. Moreover, dark sunglasses without UV protection
can potentially do more harm than good as the darkness of the lens can cause the pupil to
dilate, allowing damaging ultraviolet rays into the inner parts of the eye. Polarized lenses
provide the comfort of darkened lenses, eliminate uncomfortable and often dangerous
glare, and filter harmful ultraviolet light.
Stressed Out
There is an interesting visual phenomenon associated with polarized lenses, one that
allows stress patterns in certain materials to become visible to wearers of polarized
lenses. The effect can most often be seen in the car windows as a cross hatch pattern in
the glass. Auto glass is tempered for safety. This tempering induces stress that becomes
visible when viewed through polarized lenses. Similarly, ophthalmic lenses can be
checked for stress by holding them between two polarized lenses with light shining
through. Any amount of stress in the lens material becomes evident. The process works
for lenses of any material and is the only way to detect unwanted stress that could
ultimately result in a broken lens. This unusual feature of polarized lenses has no effect
on acuity or vision, but it may help to explain this characteristic of polarized lenses to
anyone purchasing or considering polarized sunwear.
Dispensing Polarized Lenses with AR
Something else to consider when dispensing polarized lenses; most high-end sunwear
manufacturers, in addition to using polarized lenses, add an AR coating to at least the
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