lens tips

High-index Surprises

Karlen McLean, ABOC, NCLC

High-index lenses are thinner and lighter, everyone knows that. But not so fast: That can be true only if you apply some wise dispensing tactics along with your 1.60, 1.67, 1.70, 1.71, and 1.74 index lens recommendations. To help avoid high-index rejects, follow these road-less-traveled tips.

ALWAYS DO…

■ POLISHED EDGES: Offer a high-end appearance to high-index lens edges. However, some patients may find highly polished lens edges reflective and distracting or dislike the crystal-like appearance. Many labs recommend a satin finish rather than glossy (also called “ice”) for that reason.

■ EDGE TINTS: This option helps cut down on edge reflections and can also be aesthetically pleasing. A tried-and-true application is to match the frame color on plastic frames, so lenses look like part of the frame, or flesh-colored—most popular in rimless styles—to match skin tones.

■ ROLLED EDGES: More popular in the past than now, this helps take down back-edge sharpness in a high-minus lens. Use rolled edges as a last resort for clinical rather than cosmetic reasons, as many people don't like their appearance.

■ ASPHERICITY: The most-desired feature from a visual (cuts peripheral aberrations) and aesthetic (flatter appearance, less magnification, and minification of the eye) standpoint. But aspheric with AR is the best—and what high-index lens comes without AR these days? Don't assume the high-index lens you order is aspheric; write it on the lens order.

■ CROWN GLASS: Offered in 1.80 and 1.90 indices, these are considered a specialty item available from a few wholesale labs. The concern here is safety: High-index glass lenses can't be made impact-resistant to U.S. standards, and that can leave ECPs open to lawsuits. If you dispense ultra-high-index glass lenses, experts recommend that you have the patient sign a waiver.

DO NOT…

■ RECOMMEND GROOVED RIMLESS: Because of minimum thickness standards, high-minus and high-plus lenses will be too thick, temporally and nasally, respectively, and each will have a good chance of chipping, especially high-plus.

■ PLAY WITH PRISM: Remember that base-out prism thickens the temporal lens' edge and base-in prism does the same to the nasal edge. Use a frame that covers lens' thickness, such as a rounded-edged, full-rim plastic.

■ IGNORE PANTOSCOPIC TILT: Adjusting frame panto between six and 10 degrees or as the lens manufacturer recommends is essential to help eliminate chromatic aberration. To ensure the best frame-and-lens fit, pre-adjust the frame every time. That includes panto, face-form (curve), bridge, and temple adjustments. EB