quick vision question?

Just from knowing the 20/70 and 20/50 , which is your UNcorrected visual acuity, does not give any clue as to what the prescription could be. There is no conversion possible.

You won't be able to order online even if you did know the numbers unless you have a valid prescription from the Dr. that would also specify the brand, and base curve of the lenses you can order, as well as the power.

If you need the same prescription, just contact your former doctor for the numbers you need so you can buy them another way. The doctor should do this for free; however, I have been charged as much as $25 to get a copy of a prescription. Won't go back there again. I always carry my prescription in my wallet in case my glasses break away from home.

Its impossible to tell without a refractive optical test. You could be farsighted (needing a+lens) or nearsighted (needing a -lens), or you could have astignatism, or something else. Do not guess, see an eye specialist.