Too light for sun light

My eye doctor recommended that I purchase snap on sun glasses rather than use the prescription type. It is very difficult to get a good fit for existing glasses if you don't have them in hand.The plastic is thin and flimsy--the dark part to cover the lens is not large enough to cover the lenses, and though convenient don't do the job. I was disappointed and later purchased better, more expensive glasses elsewhere. They are cheap--but you get what you pay for.