Optical power (also referred to as dioptric power, refractive
power, focusing power, or convergence power) is the degree to which
a lens, mirror, or other optical system converges or diverges
light. It is equal to the reciprocal of the focal length of the
device.[1] The dioptre is the most common unit of measurement of
optical power. The SI unit for optical power is the inverse metre
(m−1).