Hands On - ASK THE LABS
by Karlen McLean, ABOC, NCLC

WEAK AND STRONG

Q How do you measure the prescribed prism in eyewear when one lens is strong and the other lens is weak?

A When measuring prism, it's important to start with the strongest lens first. This is the lens that has the highest power through the meridian of measurement. If you are measuring vertical prism, this is the vertical meridian, and vice versa for horizontal prism.

Prism should be measured in this fashion because the lens with the highest power will demonstrate more sensitivity to movement in the focimeter by inducing more prism for the same amount of lens movement.

Note that this procedure does not apply to progressive addition lenses, which are always measured for prism at the prism reference point (indicated on the lens by the manufacturer).

The recommended methods for measuring horizontal and vertical imbalances in single vision, multi-focal, and progressive lenses are described in detail in the ANSI Z80.1 standard, available from ANSI at http://webstore.ansi.org.

— Darryl Meister, ABOM, technical marketing manager, SOLA Optical,
Petaluma, Calif.

RIMLESS RESTRING

Q What is the best way to restring a cord-mounted rimless lens?

A Practice is the best way to hone your technique. The basic technique is:

1. Thread one end of the cord into the eyewire, and insert the other end of the cord into the other side of the eyewire.

2. Place the lens into the groove in the eyewear and hold in place.

3. Slide the cord until you get in the ballpark of having it sized right.

4. Use strapping to stretch the cord around the lens tightly.

5. Using a sharp blade, cut the tightened cord on an angle.

You can practice on an old pair of eyewear to improve your speed and make yourself more comfortable with the technique.

— Scott MacLeod, lab manager, McLeod Optical Company, Inc., Warwick, R.I.

Rough Customer

Q We have a customer—an avid motorcyclist—who is constantly wrecking eyewear. What is a good, durable frame and lens choice for someone who rides a motorcycle and is very rough on eyewear?

A We work a lot with one company whose product we found in a motorcycle shop. The anti-fog polycarbonate lenses, made by Panoptix, feature a special seal with foam padding similar to swim goggles to keep the wind out. Set in a supplied form-fitting, wrap-style frame, the lenses come in different shades of polarized and photochromic as well as clear. They work with helmets and are available in plano or Rx single vision and multifocal. We also use the product as a solution for our ski/snow industry customers, and those who have chronic or severe dry eye problems. We've had no problems with the product and the warranty is solid.

— Aaron Schubach, vice president,
Standard Optical & Opticare of Utah, Salt Lake City

If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Fax: 215-643-1705. E-mail: mcleank@boucher1.com. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebusiness.com.