fix and fit

The DOs and DON'Ts of Frame Selection

by Alex Yoho, ABOM

Have you ever been embarrassed to receive a phone call from the lab telling you that a job you designed just wasn't going to work?

Here are some tips about frame selection that will keep you from getting red in the face.

Frame sizes and shapes vary tremendously and, though you now know to order a lens within range, the frame can create problems.

In general, the outer edges of a frame should be even with the widest point of the head, which is normally above the ears. But, when style dictates something larger, problems begin. Frames that are too large, as well as wrapped frames and progressive lenses, create the most problems.

PROBLEM: LARGE FRAME

Large frames are a no-brainer if you look at a cutaway diagram of a lens. The bigger the lens, the thicker it gets, especially with stronger powers.

If a patient is considering a big frame, use a lens diagram chart (available from some suppliers) to show them how thick the lens will be.

If the frame extends beyond the lens diagram, there is a problem. Another danger point is when the patient's PD is very close to the eye size. In both cases, it's time for a smaller frame.

PROBLEM: EYE SIZE

Wrapped frames are a prime candidate for the eye size problem. If, for example, you have a 60 eye frame and the patient's PD is 63, the decentration of the optical center will be way too much, and the edge of the lens blank will fall inside the lens shape.

Image courtesy of Beausoleil

To avoid ventilation gaps, stay away from these styles.

PROBLEM: THICKNESS

If the blank is not thick enough to surface out to the edge of the frame, there will be a ledge where the lens didn't surface out and it will have a myodisced appearance.

PROBLEM: PAL

The biggest mistake with progressives is not checking the cutout on the appropriate chart. Ask your lab to provide you with one for each type of progressive you use.

All you do is put a dot at the patient's pupil center on the sample lens in the frame and place the dot on the pupil location of the chart. If the edge of the frame falls inside the circle, you're good to go. If it falls outside the circle, you must select a different frame.

Following these guidelines will help keep those embarrassing calls to a minimum. When in doubt, simply contact your lab. They can help you in determining when those borderline jobs will work. And when they won't. EB