diopter (D)

The units of refracting power of lenses. It is equal to the recprocal of the focal length of the lens in meters. A 1 diopter lens has a focal length of 1 meter. A 2 diopter lens has a focal length of 0.5 meters.

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999