How much ultraviolet light should I feed my eyes?

Someone just told me it’s a good idea to expose your eyes to at least a little bit of UV light. He said it prevents nearsightedness, and he told me his vision got better while he was in the military and didn’t wear sunglasses. I wear sunglasses all the time, and underneath them, I wear contacts (which do or do not block UV rays?). Am I doomed to perpetually degenerating long distance vision? Or might I be able to condition myself back to 20/20 with a little extra time in the sun?