|Name||Symbol||Quantity||Expressed in terms of SI base units||Expressed in terms of other SI units|
|dioptre||D||optical refractive power,
reciprocal focal length
|m−1||1 / m|
The dioptre, symbol D, is a non-SI unit of measurement of the optical power of a lens or curved mirror.
The dioptre is not accepted for use with the SI.
Although the dioptre is based on the metre, it is not included in the SI. The unit for optical power should therefore be specified explicitly as the reciprocal metre, m−1.