Morning! Could do with some prescription interpretation please. I’m NHS but know nothing about eyes 
There’s an offer of a free pair of specs online. I have a “proper” pair of varifocals from a very good local optician, but thought I could use the freebie to get a pair for watersports (I lost a very expensive pair of glasses doing this last year).
However I have very bad astigmatism in one eye. The cyl measurement on my right eye is -5.00, but the online company only go down to -4.00. If it’s not a silly question, would -4.00 still give me ok vision, or is it a completely different prescription, if you see what I mean?
This free pair would literally just be for out on the water, to save my good (£400
) pair.
Any advice would be great, thank you