prism diopters are a measurement of?
The power of an ophthalmic prism (glass or plastic) in prism diopters (Δ) is equal to the deviation, in centimeters (cm), of a light ray passing through the prism, measured one meter, or 100 cm, away from the prism [Figure 1]. ... For angles smaller than 45° (or 100Δ), each degree equals approximately 2Δ.