| a unit of prismatic deviation, in which the number one represents a prism that deflects a beam of light a distance of one centimeter on a plane placed normal to the initial direction of the beam and one meter away from the prism. |
prism diopter n.
Abbr. PD
The unit measuring the deflection of light passing through a prism equal to a deflection of 1 centimeter at a distance of 1 meter.