dioptre vs diopter

dioptre and diopter both are nouns.

Word	Noun	Adjective	Verb	Adverb
dioptre	Yes	No	No	No
diopter	Yes	No	No	No

As nouns, dioptre and diopter are synonyms defined as:

dioptre and diopter: a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists

dioptre (noun)	diopter (noun)
a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists	a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists