Lens & Frame Measurements & Markings

geometric center (GC)

point on the horizontal midline halfway between the lens bordering vertical lines

A

eye size or lens size; the horizontal measure of the lens within the boxing system

B

the vertical measure of the lens within the boxing system

C

width of the lens itself along the horizontal midline; rarely used

effective diameter (ED)

found by doubling the longest radius, which is the distance from the GC to the apex of the lens bevel farthest from it

distance between lenses (DBL)

distance b/t the 2 lenses when both lenses are boxed off in the frame; aka bridge size; measured on the frame as the distance from the inside nasal eyewire grooves across the bridge area at the narrowest point

geometric center distance (GCD)

distance b/t the 2 GCs of the lenses; can be measured more easily as the distance from the far left size of one lens opening to the far left side of the other; can be calculated by adding the eye size to the DBL; aka frame PD

frame difference

difference between the horizontal & vertical measurements

A

1

geometric center

2

datum line

3

effective diameter

4&5

DBL

7

geometric center distance

6

C

8

seg drop

9

seg height

10

B

11

A

55 corresponds to what measurement for this pair of glasses?

DBL

13 correspondences with what measurement for this pair of glasses?

temple length

140 corresponds with what measurement for this pair of glasses?