Great question- We have actually gone as high as -28 on one eye and -21 on the other as in this mask below. We actually have a post about
prescription strength on our site.
This was a pretty cool project for a unique customer that always wanted to scuba dive, but could not.
I don't have any way to prove it, but I believe this may be the stronger prescription put in a dive mask ever.
Positive corrections are interesting and can be more challenging, as in dive mask the entire prescription is surfaced into the back of the lens due to the need for the front of the lens to be flat (plano in optical lingo). We have gone as high as +10, but could likely go a bit stronger.
On the super strong prescriptions, we do land up with a smaller piece of glass to work with, and it becomes increasingly important for us to know exactly where your eyes sit in the dive mask.
By graded, do you mean a tint that goes in a gradient across the lens, or a tinted lens. We are experimenting with some different tints, and do offer them on a special order basis (although this does add time), but we are not offering them widely yet.
- Josh