Frame PD is defined as Distance PD divided by 2. Which term describes this measurement?

Frame PD is defined as Distance PD divided by 2. Which term describes this measurement?

• A. Inset
• B. Seg Inset
• C. Total Inset
• D. Vertex Distance

Answer: (A)

Pupillary distance is the distance between the centers of the pupils. When you translate that to the frame, you take half of that distance for each eye, giving the amount the frame is inset toward the nose on each side. That per-eye half-distance is called the inset. So frame PD = PD divided by 2, and the term describing this measurement is inset. Vertex distance is a different concept (distance from the cornea to the back of the lens/frame), and seg inset refers specifically to how a bifocal segment is positioned, not the general per-eye frame measurement.

Pupillary distance is the distance between the centers of the pupils. When you translate that to the frame, you take half of that distance for each eye, giving the amount the frame is inset toward the nose on each side. That per-eye half-distance is called the inset. So frame PD = PD divided by 2, and the term describing this measurement is inset. Vertex distance is a different concept (distance from the cornea to the back of the lens/frame), and seg inset refers specifically to how a bifocal segment is positioned, not the general per-eye frame measurement.