Nearly every dive shop can provide standard corrective lenses for a mask, with different corrections for each eye, based on dioptor parameters (I think by 25 degree differences). If you need more precise correction (including astigmatism, etc.), most opticians can obtain more finely corrected lenses for masks. I am nearsighted and manage to get good results with the standard corrective lenses which are closest to my specific perscription. (I don't bother with the astigmatism issue, since it is not too serious for me. If it was, I would go for the optician alternative.) In any event, the alternative of corrective lenses in your mask seems a lot easier than trying to learn to wear contact lenses for snorkeling or diving. Cheers, Fred