ASK THE LABS
By Joseph L Bruneni

Large Eye Sizes�30 Years Later
Q What�s the trade-off in optics with the new large size frames that were popular in the �70s and now seem to be coming back in style? I recall that labs hated them, and the peripheral optics were inferior. I haven�t stocked these yet and wonder if new lens technologies and designs will eliminate this concern?

A As we use larger lenses, weight and peripheral optics are pushed toward their limits. We are in a much better situation today to deal with these problems than in the 1970s when most lenses were CR 39. Today�s newer materials with higher indices of refraction and lower specific gravity compared to CR 39 make it easier to fabricate a large lens that is both thinner and lighter.

One potential drawback, however, is that the newer materials can have more chromatic aberration than CR 39. This is not desirable, but will likely not be a serious problem. Chromatic aberration is primarily a problem for foveal vision. Our fixation field is usually smaller than even the smallest frames we use today. Going to a larger lens in a larger frame will not cause us to fixate more peripherally than we already do�therefore, increased chromatic aberration in the periphery will not be particularly problematic. Our biggest advantage today is that we now have aspheric lenses.

We are much better prepared to handle large eye sizes because of new lens materials that have higher indices of refraction and lower specific gravity and aspheric designs. Fewer vision compromises will be caused by large eye sizes.

�James Sheedy, O.D., PhD, University of California, School of Optometry

Titanium is Forever�Sometimes
Q We just had a titanium frame come in that was broken at the hinge. We have heard that titanium can�t be soldered but wonder if that�s true, how are the frames manufactured? Is it possible to repair titanium?

�Roger, Precision Eyewear

A Titanium can be soldered but the process requires equipment that is so specialized and expensive, it�s impractical to do anywhere but in a manufacturing environment. Titanium requires a high temperature soldering process that takes place in a chamber in which the atmosphere is tightly controlled to eliminate oxygen. Done properly, a titanium solder joint is extremely tough and is why our company, for example, will replace free of charge any titanium frame that breaks. Even our Training Lab does not offer that service.

�Carol Norbeck, VP, special projects, Silhouette

SPF for the Eyes?
Q What benefit is there in having melanin in sun lenses? Who makes them, and what lens forms are they available in?

�Lisa Smith, The Optical Shoppe

A Melanin lenses are polarized and provide protection, performance, and comfort in the sun by absorbing harmful UV sunlight, associated with the development of cataracts, and High Energy Visible (HEV) light that has been linked to macular degeneration. Because they are polarized, they reduce reflected glare (polarized filter) while improving contrast and maintaining true color balance. They are manufactured by Specialty Lens Corporation with license by Photoprotective Technologies. They can be ordered in SV, D-28, D-35, 7x28, 8x35 and progressive lens styles through wholesale laboratories.

�Eric Lindquist, marketing manager, Specialty Lens Corporation