ask the labs

Perplexing PALs

Susan P. Tarrant

Q Is there anything wrong with ordering progressive lenses with differing add powers? I always thought the adds should be the same for best binocular vision, but maybe I’m wrong. In one particular case, I got an Rx that called for OD +1.75 add, OS +2.00 add. What’s the best course of action here?

A I don’t believe that there is a problem doing different adds as long as the patient understands up front that his peripheral vision may be slightly better in the OD than the OS. As far as the power gradient is concerned, it is all relative, so that’s not really a concern.

What I would be more concerned with is that lenses have greater peripheral astigmatism as the add power increases (or, in other words, the lenses “get narrower” in higher adds). So that’s why I say there could be a difference in peripheral vision.

In my experience, we have done thousands of progressives with split add powers and I have not seen any increased trend on non-adapt rates in differing adds as opposed to matching adds.

— Jason Mansuy, vice president, operations, Vision Craft, Walled Lake, MI

Q Can progressive addition lenses be slabbed off? If so, what’s the best way to do it?

A The simple answer is ‘yes,’ they can be slabbed-off. Approximately 30 percent of our slab-off lenses ordered daily are in the form of progressive lenses.

One thing you need to know when ordering a slab-off is the fitting height of the slab line. The fitting height of a progressive lens and the slab line height are not the same. The default height in our software is 4mm below the datum line, or 180 line. You can change that line to be any height depending on the patient’s need or frame selected. If the B measurement is small, you may want to change the height to 2mm or 3mm.

Also, consider the lens design you are ordering. If it has a fitting cross of 2mm or 4mm above the datum line, you may want to change the slab line. There is no need to calculate the slab-off prism, as the lab software will do it automatically and precisely.

If you have a patient who is having reading problems or experiences eye fatigue while reading, you should consider a slab-off. We do slab-off lenses as low as 1 degree of prism or as high as 15 degrees of prism.

— John Haskins, president, Slabs Plus, Ruskin, FL

If you have a question you’d like to have answered in Ask the Labs, 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.

SHARE YOUR CHALLENGING Rx’s

Did you ever get a prescription or a patient with unique visual needs that temporarily stumped you? What did you do to solve the issue? We’d like you to share the story with us.

Eyecare Business is looking for optical professionals—opticians, ODs, lab techs—to share the Rx’s that truly presented a challenge, and how they handled those challenges. It’s all in an effort to learn from each other. Please send your story to senior editor Susan Tarrant at susan.tarrant@springer.com, and we’ll consider it for publication.