troubleshooting tips
Busting Optical Myths
by Karlen McLean, ABOC, NCLC
Optical myths and legends abound. We picked some favorite lens myths and asked experts to bust them.
PHOTOCHROMIC CHILL
Myth: To initially best activate a photochromic lens you have to take it out in cold weather or put in the refrigerator.
Busted: Putting a lens in the refrigerator will not help the long-term darkness of a photochromic lens. This myth is linked to how the darkness of all photochromics depends on the temperature and the amount of UV light.
Outdoors, a photochromic lens will be darker when there is more UV light and less dark when there is less UV light. The temperature works in the opposite direction: a photochromic lens will be darker at lower temperatures and less dark at higher temperatures.
The overall darkness of the lens will then depend on the balance between the amount of UV light and temperature.
It's worth noting that, to counteract the effect of temperature, the latest generation of Transitions VI lenses was specifically designed to be much darker at higher temperatures than previous generations.
— Brian Hauser, director, lens manufacturer and trade channel sales, Transitions Optical, Inc.
| SPORT RETORT |
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| MYTH: Polarized lenses are unsafe and ineffective in certain outdoor sport situations, such as with snow skiing (mogul identification) and golf (identifying the lie of the grass). BUSTED: When polarized lenses were first worn, they were largely replacing tinted dark sunlenses. The tinted lenses didn't block blinding glare. Polarized lenses do block blinding glare and, as a result, the visual acuity in bright light conditions is vastly improved. This results in more visual information being available to the brain and thus being processed differently by the brain, which may have led to the ‘myth’ that they are ineffective. The belief is that the brain has to work with polarized lenses. If, on the other hand, you have only had polarized lenses, there is no relearning to be done. — Dr. J. Sidhu, Younger Optics |
FREE-FORM FIELDS
Myth: Free-form/digitally surfaced lenses are marketing hype, they really aren't the top of the top.
Busted: There is no truth to this myth. Free-form lenses provide a surfaced job that's superior in accuracy, plain and simple.
The reason for this is that the back surface of the lens is computed to the nearest 0.01 diopter, and because conventional tools are not used, it can be surfaced to that level of accuracy (tolerances still apply).
With conventional surfacing, the curve is rounded to the closest tool curve being used in the lab. This can be 0.06, 0.10, or 0.12 diopters, plus the tool is compensated for the thickness of the pad to obtain the correct curvature to create the correct power.
All of this can exacerbate loss of accuracy.
Design that is 100 percent on the lens' backside provides a wider field-of-view because the design is closer to the eye. Combine wider field-of-view with a more accurately produced Rx, and the result is a superior product over conventional methods.
— Jerry Thornhill, technical services manager, Shamir Insight, Inc.
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