ASK THE LABS
By Joseph L. Bruneni

Color Me Healthy

Q A local ophthalmologist has asked us about a lens discussed in a recent MD publication. The lens is called FL-41 and has a color tint that is reported to effectively treat light sensitivity in patients with blepharospasm. What can you tell us about this FL-41 lens?

�R. Emil Hagman, Ohio State Optical, Columbus, Ohio

A Kathleen B. Digre, M.D., professor of Neurology and Ophthalmology with the Moran Eye Center at the University of Utah, wrote the article your doctor saw. The Knighton Optical dispensary in the Moran Center developed the FL-41 lens at her request. Manager Chuck Swallow reports that the rose brown tint was originally reported in the U.K. for helping adolescents suffering from migraine headaches. Digre prescribed the FL-41 lens for a young migraine patient who also had blepharospasm complaints. The mother reported back in tears the first day to say that the new glasses for the child�s migraines had stopped the spasms. Success has also been reported for photo-induced epileptic seizures in adolescents (but not adults).

Utah TV station ran a news story about the lens that produced a flood of calls to Knighton Optical on the following day. The story was later picked up by the network and has appeared in a number of cities. Calls about this interesting lens can be directed to Chuck Swallow at 801-585-7800.

Swirling and Twisting

Q As an experienced dispensing and finishing optician, I have noticed certain aspects of poly. One of these is the �swirled� appearance to the lens surface in certain angles of viewing. What causes this? Also, I�ve noticed that, even when edged to the proper size, this lens material will tend to turn more easily with pressure from an axis-aligning tool. Is this related to the particular material that is poly?

�Lyle Waller, Wal-Mart Vision Center, Montrose, Colo.

A The �swirl� effect the optician is referring to is defined as birefringence, or the refraction of reflected light seen from a coated surface. As index of refraction differences increase between the coating and substrate, visibility of birefringence also increases.

Manufacturers provide extensive research into coating properties, including this aspect as well as adhesion, durability, scratch resistance, AR coating compatibility, and tint absorption (to name a few). When evaluating the best coating, the birefringence is typically least important since it has no effect on patient acceptance. All manufacturers continue to improve coatings for all aspects, but to date no coating does it all. It is important to choose a coating product that meets the individual needs. Note that even flat glass surfaces placed against each other will exhibit birefringence.

As to the next question, polycarbonate lenses may rotate in a frame somewhat easier than other plastic or glass lenses, though I�ve never seen this suggested before. It is not considered a problem. Similar to the molecular properties of polycarbonate string-like bonds which give the material its strength, this also provides a �slicker� surface. Even though polycarbonate lenses might be easier to turn with axis pliers, we recommend attempting to insert the lenses on axis. Axis pliers have long been known to damage many plastic lenses.

�Denny DeCourcy, Vision-Ease Technical Services

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