Why do nearsighted (or short-sighted) people sometimes gain better far/distance vision when their eyes are developing cataracts?

A cataract is the natural lens that has undergone age-related degenerative changes. So as a lens, it has a prescription, much like your glasses have a prescription. As the natural lens goes through the age-related degeneration that results in it becoming a cataract, the slight changes in size and density cause a change in its Rx as well. This can in many cases be enough to change the focus of one's vision, usually towards becoming better at near.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic