I don't currently have a copy of my glasses prescription (I have requested but not sure how long that will take) but am I right in thinking that if I wear contact lenses in -3.25 and -3.75 then -3.5 and -4 is the strength to go for in goggles. I have a mild astigmatism but it's not corrected for in my contact lenses if I remember correctly. I'm not looking for perfect correction, just something so I can see signs, the clock, people in blue swimming costumes etc.