What is the optical power of glasses with a concave lens if its focal length is 50 cm?

What is the optical power of glasses with a concave lens if its focal length is 50 cm? What are these glasses for?

f = 50 cm = 0.5 m.
D -?
The optical power of the lens D is determined by the formula: D = 1 / f, where f is the focal length of the lens.
For a convex lens, the optical power is D> 0, for a concave lens, D <0.
D = 1 / -0.5 m = -2 diopters.
Such lenses are used for people who suffer from myopia, who cannot see distant objects.
Answer: the optical power of the glasses is D = -2 diopters.