They don't relate directly to your eye prescription for complicated reasons. That's why it's easier to go to one of the London Leica dealers and try a few out. I bought a second hand one that worked for me. Leica accessories are all silly money though!
Interesting to know, reading about online it seems people are happy with whatever they prescription says. Off to Manchester in a few weeks so I'll pop to the Leica store and try a few I guess.
They don't relate directly to your eye prescription for complicated reasons. That's why it's easier to go to one of the London Leica dealers and try a few out. I bought a second hand one that worked for me. Leica accessories are all silly money though!