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Karlen McLean, ABOC, NCLC

Know Your ABEDs

One of the first things I learned as an optician, after mastering how to take a PD, was how to take frame measurements and utilize the boxing system.

The boxing system for frame measurement is the industry standard. It's taken in millimeters, typically by using a PD ruler. This system correlates letters to certain lens diameters and draws a square shape (a box) around the lens.

Here are the bare bones of the boxing system, focusing on measurements that your lab must have to properly fabricate lenses for the frame.

A: Horizontal measurement or eye size—the farthest distance from the temporal to nasal lens edge.

B: Vertical measurement or frame depth—the farthest distance from the top and bottom of the lens edge.

ED: Effective diameter—diagonal measurement (or the measurement of the longest point to point of the frame from bevel to bevel). The effective diameter typically indicates the diameter of the lens cutout and minimum blank size.

DBL: Bridge size—distance between lenses measured from bevel to bevel at the narrowest point.

SEP HEIGHT: The height of a bifocal or multifocal given as the distance from the bottom of the inside of the eyewire or the edge of the box to the top of the segment.

While most manufacturers print frame sizes on their frames (52=A measurement, 16=DBL), they may or may not be consistent with the actual size and include the ED.

It's good to get into the habit of taking your own measurements, especially since today's highly styled frame shapes can yield some unusual measurements. EB

Other Box Measurements

These measurements aren't usually supplied to the lab, but are part of the boxing system:

DATUM LINE: A horizontal line drawn through the center of the lens.

GC: Geometrical center—the point where the datum line and horizontal centers connect.

GCD: Geometrical center distance, also known as DBC (distance between centers) or frame PD—the horizontal distance between the geometrical centers of the lenses. Can be factored as the A dimension plus the DBL.

Senior editor Karlen McLean has been in the optical industry for 35 years. She has spent half of that time in the dispensary. In this monthly column, she will share her own experiences, and we hope you'll share yours. Contact her via email at karlen.mclean@wolterskluwer.com.