You should check directly with the CAA to be sure, but somewhere in the EASA medical documents, the refractive error is defined as the error in the worst median, so that means it's the sum of the sphere + astigmastism.
Thank you. Do you know if the maths rule of negatives and positives applies? Eg. negative and negative = plus. Sounds really stupid but if unsure, no worries. I'll clarify with the CAA. Thanks.