A patient has a PD of 65 mm, with frame measurements of A = 53, B = 49, and DBL = 18. How much will each lens need to be decentered?

To determine how much each lens needs to be decentered based on the given values, we first need to compute how the pupillary distance (PD) and frame measurements interact.

The total width of the frame can be calculated by adding the A measurement (the horizontal width of the lens) to the distance between the lenses (DBL), which gives us the total frame width. In this example, the total frame width is 53 mm (A) + 18 mm (DBL) = 71 mm.

Now, to find out where the optical center of each lens should align based on the patient's pupillary distance, we can find the difference between the total frame width and the pupillary distance:

• Total frame width: 71 mm

• Pupillary distance: 65 mm

The difference between the frame width and the PD is 71 mm - 65 mm = 6 mm.

This difference represents the total decentration that needs to occur because the optical centers of the lenses must align with the patient's pupils. Since there are two lenses, this total amount needs to be divided equally between both lenses. Thus, we take the total decentration needed (6 mm) and divide it by 2, resulting in a