Box Measurements

Question 1

“A” measurement

Answer 1

Horizontal distance between temporal and nasal edges of lens shape

Question 2

“B” measurement

Answer 2

The verticle distance between the top and bottom edges of the lens shape

Question 3

Geometric Center/Point “C”

Answer 3

The geometric center of where line “A” intersects with line “B”

*dont confuse with optical center of a lens, this can only be found with lensometer

Question 4

Effective Diameter (ED)

Answer 4

Edge to edge measurement from geometric center (diagonal)

Question 5

Distance between the lenses (bridge size)

Answer 5

Shortest distance between nasal edges of each lens

Question 6

What is a box number

Answer 6

The “size” of a set of frames, stamped onto frames

Question 7

Frame distance between centers (DBC)

Answer 7

Horizontal distance “A size” between the geometric centers “C point” of the lens

Question 8

Lens Distance between optical centers (DBOC)

Answer 8

The distance between optical centers of the lens is the distance from one optical center of mounted lens to the other

• the measurement must be the same as the PD and aligned with the patients visual axis

Question 9

What is vertex distance (VD)

Answer 9

Distance from the surface of the cornea to the back surface of a lens as it sits in a frame