ask the labs

easy Double-D Segs

by Karlen McLean, ABOC, NCLC

D SIMPLE TRUTH

Q When it comes to fitting double-D segs, I'm feeling a bit insecure. What's the best way to go about filling these Rx's?

A At first glance, an optician may be intimidated when called upon to fit a double-D bifocal, but there is really nothing tricky about them. Double-D bifocals are useful for patients who need near and/or intermediate vision above and below.

Double-D bifocals are generally available in 28mm or 35mm segs in either CR39 or glass. Depending upon the manufacturer and the lens material, the distance separating the two segs can be anywhere from 13 to 15 mm. Generally speaking, FT28 double-D's in glass or plastic have a separation of 13mm to 14mm, while FT35 double-D's have a separation of 14mm to 15mm. Check with the manufacturer for exact specifications.

To fit a double-D bifocal, do exactly as you do for a normal flat top. Fit the seg of the lower bifocal so it is even with the patient's lower lid margin. The top seg will automatically be where it needs to be.

The more tricky aspect of a double- D is selecting the optimum add powers. They are generally available two ways: with the same add power in the upper and lower segments for patients who need reading both above and below, or with 50 percent of the add power in the top segment for patients who need intermediate upper vision.

The key here is to talk with the patient and get a good idea of how they will be using their bifocals. Properly selected and fitted double-D bifocals can make a significant quality of life improvement.

— Wes Palmer, sales & marketing director, Optic Blue, Lubbock, Texas

If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean via e-mail at karlen.mclean@wolterskluwer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebusiness.com.