troubleshooting tips

Managing Lens Materials

Karlen McLean, ABOC, NCLC

So many lens materials, each with their own unique attributes, and so little time, it seems, to understand the nuances of each.

To help, we asked a few experts to answer the following: "What are some common dispensing misconceptions and challenges with specific lens materials, and what can ECPs do to proactively address them?"

1.67

Some ECPs measure optical center (OC) heights for single vision, high-index lenses in order to minimize chromatic aberration. Although this does minimize lateral chromatic aberration during far vision, it results in several other compromises:

1. Vertical decentration increases the job's blank size, resulting in thicker lenses;

2. Lateral chromatic aberration during near vision is increased; and

3. Oblique astigmatism is induced if the lenses have pantoscopic tilt.

For the best results, guide patients to frames that keep the eyes centered. Ideally, the pupil centers should fall within 5mm or so of a frame's datum (180 degree) line. The frames should have 8" to 12" of pantoscopic tilt. This relationship will minimize both oblique astigmatism and lateral chromatic aberration, without the need for OC measurements, while ensuring the smallest practical lens diameter.

— Darryl Meister, ABOM, technical marketing manager, Carl Zeiss Vision

1.70

A common misconception is that, since 1.70 is a super thin lens, it'll be naturally slimmer in any frame. This is an error and can lead to patient dissatisfaction.

Always choose a frame with a frame pupillary distance (FPD = A + DBL) that's equal to or within 4mm of the patient's PD. This reduces the amount of decentration required to horizontally align the lens' OCs with the patient's pupils. The more decentration required, the thicker the lens will be temporally for minus powers and nasally for plus powers.

For high-powered prescriptions, choose small frame sizes to control lens thickness.

— Brad Main, manager, training and technical resources, HOYA Vision Care North America