"We randomized patients with blepharospasm to wearing FL-41 sunglasses for two weeks and then to wearing plain sunglasses for two weeks," said Dr. Katz. "The patients filled out questionnaires at the end of each period. We found that patients with blepharospasm definitely preferred wearing lenses with the FL-41 tint to wearing conventional sunglasses. So there does seem to be some therapeutic benefit."

In a new study, the researchers have used electromyography to measure blink frequency, duration and amplitude in blepharospasm patients while they read for five minutes at a time with regular eyeglasses, glasses with a light gray tint or glasses with an FL-41 tint. The results are still being analyzed, but Dr. Katz said they appear to provide more objective evidence that FL-41 does reduce blepharospasm.

"FL-41 lenses are non-invasive, they have no side effects and they're not expensive," Dr. Katz added. "So it's a cheap, easy way to improve the lives of these patients, who in some cases are very disabled by their disease."

Be sure glasses block blue-green. FL-41 lenses are available in optical shops, but Dr. Digre cautioned that some so-called FL-41 lenses are not the real thing. "You really have to know whether the lenses are real or not." she said. "Some lenses can look like FL-41, but they don't act like it. We have done spectral analysis of our lenses to make sure they are blocking the right light".