The water alone provide some correction i think it a value of 1 so when you get a prescription mask, as i understand it, and you need a 2.5 they put a 1.5 in the mask anad the other 1.0 is handled by the water. thats for far sighted folks. i use contacts also. to have a mask done would require two masks to be fitted. the folks that did my mask in Ill said most people get just one eye done for gage reading when you are far sighted. near sighted is a whole different thing. With contacts you can use any mask. I use soft lenses and throw away after the diving is over. I wear glasses but use contacts for diving only. I also have masks with the near correcton in the lower of the glass. it only has to be close so perfection is not a big deal. If you need a 2.0 and your mask is a 1.5 you are good to go for the dive. Its not like your using that script all day. My mask fromt is flat and about 1/3 up from the bottom it bevels toward my lip so it is the right angle to read gages. you look down through a flat glass the same as you look forward through a flat glass without having to tip your head.