Astigmatism calculator

Dear endmyopia-fellows,

Our new, friendly ophtalmologist saw my son yesterday and gave him a reduced prescription for school when looking at the black board.

Her prescription indentifies a tiny bit of astigmatism written in plus dioptres.

I wanted to ask for the link to a calculator which re-calculates his astigmatism prescription into minus values?

Thanks a lot!



Thank u!