ask the labs

Polarized Pointers

Susan P. Tarrant

With the release of Transitions Vantage lenses, patients now have the option of a lens that adapts to changing light conditions by darkening as well as increasing in polarization. But for anyone doing in-office surfacing or finishing, the polarization factor necessitates a few extra—and important—steps in the process.

“Like polarized sunwear, the lenses need to be properly aligned before processing,” says Jim Schafer, technical support manager for Transitions Optical, Inc. “The axis of polarization should be aligned on the 180-degree axis line. Once aligned, Transitions Vantage lenses can be processed like any other lens.”

POLARIZED POINTERS

Though the lenses are clear and not polarized in their non-activated state, they still require the same attention to alignment that other polarized lens products need.

To keep you at the top of your game, here are some polarized pointers for surfacing and finishing, courtesy of Transitions Optical, Inc.

1 LENS MARKINGS. Angle brackets on the temporal and nasal edges of the lens and two “T” or “plus” marks denote the proper axis of polarization for the lens. The “T” markings are located 20mm off the center of the lens to avoid interfering with digital and free-form markings. These will be your guidelines for ensuring the lens is aligned correctly through the processes.

2 BLOCKING. When putting the lens on the blocker, check that the markings are on the horizontal axis, or the 180-degree line. For full backside products, use the engraved micro circles for alignment during finish blocking. For non-full backside products, use the remaining “T” or “plus” markings.

3 SURFACING. All polarized lenses can now be surfaced like any other lenses.

4 EDGING. Some of the markings will be removed during the edging process, but the remaining marks are permanent. They will not interfere with the wearer's vision.

5 INSPECTION. After mounting into the frame, inspect the lenses to ensure proper alignment, otherwise, the wearer will not get the full benefits of polarization. Look through the lenses for the “T” or “plus” markings and dot them with a marking pen. The markings should fall on the horizontal plane of a lensometer.

6 CROSS-POLARIZE. If, for some reason, the markings were completely removed or cannot be located, activate the lens fully (under a UV demo lamp) and cross-polarize it with a piece of polarized film. Hold the film over the lens with the sticker in the upper right corner, then rotate the film 90 degrees.

The lens should appear darker than in the previous position, Schafer explains: “When polarized lenses are crossed, 90 degrees opposite each other, the lenses are darker than when overlaid at the same polarization orientation.” EB

If you have a question you'd like to have answered in Ask the Labs, please send it to Susan P. Tarrant. Email: Susan.Tarrant@Springer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business website at eyecarebusiness.com.