I had this problem a while ago, I asked on another forum what correction was needed for pistol shooting and got this reply.
Pistol shooters aged up to 40 +0.50 aged 40 and above +0.75.
I went to a local optical manufacturing firm with my latest eye test result, this is after cataract replacement in both eyes,they understood the numbers, that I don't, I left the lens holder with them and a week later had a lens that enables me to see the foresight very well, all for £30.
Pity about the tottery old OAP who can only manage supported pistol now.