Meaning of prism diopter

prism' diop'ter

Pronunciation: [key]
— Optics. Optics.
  1. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.