Interpupillary and centration distances

Question 1

Define:

Pupil Distance (PD)

Answer 1

Pupillary distance is the distance measured in mm between the centers of the pupils.

Question 2

Define:

Near centration distance (NCD)

Answer 2

near centration distance is the distance between where the converging visual axes of the right and left eyes meet the spectacle plane.

Question 3

How to measure a PD for someone with strabismus

Answer 3

Cover test - align the ruler binocularly then occlude each eye in turn to achieve an accurate PD measurement