Ask the Labs
ask the labs
Susan P. Tarrant
Q Which lens materials are best for PALs with high cyls?
A When it comes to selecting which material is best for progressives with high cylinders, the natural thought would be to select a material with a lower Abbe value in an attempt to reduce both unwanted astigmatism and magnification typically associated with thicker lenses.
Though in theory this rings true, practical application has proven that today’s higher-index materials, including polycarbonate, are typically well received by patients—especially when combined with a quality progressive lens design.
As always, however, a quality laboratory can and should be an ECP’s most trusted source for information; and they can work with offices to best resolve whatever visual situation presents itself.
— Jeff Szymanski, vice president, Toledo Optical, Toledo, OH
Q I have a patient who is extremely hard on his glasses, so we tried crown glass lenses to lessen the problem of scratches. But he complained of seeing little “halos” of blurry light on the left and right of the lenses. I assumed they were the ID watermarks. They bothered him, so we switched him back to his original lens material. But I’m left wondering if that is a problem inherent to glass PALs? I don’t dispense much glass at all, so this was a new one for me.
A Lens ID watermarks are usually invisible to the patient, as they are far enough in the periphery, and I do not believe that they would cause enough aberration effect to produce the “halos.” What seems to be a more noticeable difference would be in the progressive design. Progressive lenses in crown glass have a very limited availability, and more than likely a very early design with narrow corridor widths would cause “halos” if the patient catches the edge of the corridor zones.
CR-39 plastic lenses have a broader range of availability and a more advanced choice of designs to choose from that provide patients with increased corridor width and clarity.
The free-form digital lens market has exploded with so many opportunities that patients now can have a customized and optimized lens that will absolutely eliminate those oblique aberrations that can cause “halos” as well as so many other irritating effects that can lead to patient dissatisfaction. Combining those lenses with today’s tougher coatings can provide the patient with the best visual experience while combating those recurring scratches.
— Denise Capretta, COMT, LDO, ABOC, NCLC, technical marketing and education manager, VSP Optics Group, Rancho Cordova, CA
|DESIGN VS. MATERIAL
Eyecare professionals are constantly confronted with the challenge of choosing the material and design that will give patients the best vision while looking aesthetically pleasing. Which one can do the better job? Jeff Szymanski offers this:
“A better progressive lens design trumps the less impactful decision of material choice every time. The degree of precision and pinpoint accuracy inherent in the digital fabrication process with progressive lenses produces such an exacting product that material selection in those circumstances becomes almost irrelevant.”
If you have a question you’d like to have answered in Ask the Labs, send it to Susan P. Tarrant. Email: Susan.Tarrant@Springer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business website at EyecareBusiness.com.
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