If the distance PD is 64 mm and the near PD is 60 mm, what is the seg inset?

If the distance PD is 64 mm and the near PD is 60 mm, what is the seg inset?

• A. 8 mm
• B. 4 mm
• C. 2 mm
• D. 0 mm

Answer: (B)

Seg inset is how far the near segment must be moved toward the nose so the near vision line aligns with the pupil. Since near PD is typically smaller than distance PD, you inset by the difference between them. Here, distance PD is 64 mm and near PD is 60 mm, so the difference is 4 mm. Therefore, the seg inset is 4 mm. If both PDs were equal, no inset would be needed; if near PD were larger, you’d adjust in the opposite direction.

Seg inset is how far the near segment must be moved toward the nose so the near vision line aligns with the pupil. Since near PD is typically smaller than distance PD, you inset by the difference between them. Here, distance PD is 64 mm and near PD is 60 mm, so the difference is 4 mm. Therefore, the seg inset is 4 mm. If both PDs were equal, no inset would be needed; if near PD were larger, you’d adjust in the opposite direction.