fix and fit

Working with Plastic Frames

by Alex Yoho, ABOM

While patients may be willing to put up with some discomfort for the sake of getting the just-right look in plastic frames, they are creating fitting challenges for dispensers. The only function of the bridge is to bear the brunt of the eyewear weight on the nose—and the more area covered, the less pressure on specific points.

The problem arises when only a small area of the available bridge surface makes contact with the nose, such as when the bridge is too wide to allow the sides to contact the nose. As a result, all of the weight of the frame is borne by the top of the nose, creating the dreaded pressure marks on the nose.

WORKING THE ANGLES

What we need to keep in mind when selecting a frame for the patient is the shape of the nose itself. There are three angles that should be considered at all times.

■ FRONTAL ANGLE: The frontal angle (think of a roof peak and how the roof angles down from that peak) can have a steep angle with nearly straight sides, or a very wide angle that goes almost straight out from the peak. The bridge must match the frontal angle.
■ SPLAY ANGLE: The splay angle runs from the tip of the nose to the base of the nose. The bridge surface must be in constant contact from front to back. If not, you will see pressure marks either near the front edge or the back edge. This is important to watch for when selecting a plastic frame as the bridge is virtually a fixed component.
■ PANTOSCOPIC ANGLE: With adjustable pads we would be concerned with the vertical angle, but with a plastic frame it is not a factor. An exception would be adding pantoscopic or retroscopic tilt to a frame that changes the vertical angle slightly.

Because the nose has a compound angled surface, it is possible to change the pantoscopic angle to improve the fit of the frontal angle.

For example, if there are slight gaps at the lower area of the bridge, adding pantoscopic tilt by angling the temples down will take advantage of the splay angle of the nose, moving the lower area of the bridge toward the broader base of the nose. This adjustment will not only close the gaps but will also improve the overall weight distribution.

Some plastic frame bridges can be customized as the eyewear is being manufactured. These customizations may be found in past Fix & Fit articles at EyecareBusiness.com.

Keeping in mind the thoughts above should help you give your patients the most comfortable eyewear available. EB