Q. A Progressive Conundrum-design problem or fitting problem
With all the change in stated acceptable seg-heights, we find that the addition reached in the lens may be 0.5 to 0.75 diopters less than that prescribed by the doctor. Is this filling the prescription as written?

-Andy Winters ABOM, COA

A.
Design Considerations
I agree that there are no standards on this issue. Some believe that when you reach 85 percent of the add power, then that is the correct length of the corridor. Others measure from the prism reference point where the official corridor begins, but that doesn't account for the 4mm further up to the pupil center.

When we measure a corridor at the lab, we measure the length from the last of plano power (all samples are ground to plano distance) to the beginning of the add power as printed on the lens. Even with this approach, it is only the beginning and not the full width of the add. 

To reach the point of the widest section of the reading area, the add power is frequently above the power indicated on the lens.

Basically, we had to take a position that was repeatable, and I feel this is best because it's simple to undestand. In a separate issue, we find in our Mystery Shopper program that 71 percent of the PALs are [fit] in error. I blame this on poor training (parallax when the optician only uses their dominant eye to fit both of the patient's eyes) and short cuts.

-John Young, Colts Laboratories

A.
Refraction Considerations
Due to today's small frame sizes and short "B" dimensions, some progressive prescriptions are not being filled exactly as written because the add part of the lens is being cut off. In some cases, there is a small, but useable, reading area with the proper add prescription. It is a judgment call to decide how much of the seg needs to be present in order to be functional to the patient.

Certainly with higher seg heights comes wider reading zones, but many patients are perfectly happy losing some of their width in order to wear the frame style they like.

In my opinion, the new minimum seg height per the manufacturer is a good guide to the dispenser because it does still preserve enough reading area to be functional. If the fitting height as measured on the patient is more than 1 or 2 mm shorter than that minimum, I believe the dispenser should call the prescribing doctor and ask if the add power could be increased by .25 or .50 to compensate-or else guide the patient to select a different frame.

-Neil B. Gailmard, O.D., MBA, FAAO, Gailmard Eye & Laser Center, Munster, Ind.

Q. Allergies and nose pads

A.
This could be a latex allergy issue. All our pads are latex-free but some pad manufacturers do use latex. Some patients are even allergic to latex-free materials. This is why we recently added two new nose pad materials. One is made of Bohemian Crystal. The second is 100 percent titanium and helps with nickel-free concerns and other potential allergy issues.

-Bob Woyton, product manager, Hilco.EB

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