A lens in a pair of glasses not only changes the focal point, it changes the size of the perceived image, magnifying it or minifying it (which it does depends on whether you are nearsighted or farsighted),
and how much
the size changes depends on
the power of
the lens.
The brain can adapt to small differences in image sizes between the two eyes, but larger differences can be harder, or not possible, to adapt to. How much difference each person can tolerate varies.
. e.g.