Lemon and Eyebright (Dr. Crhistopher) eyewashes?

If anyone is doing this, i hope you can answer a few questions:

First, how much liquid can an eyecup normaly contain? Recomended 3-4 drops of lemon kind of stings in 15 ml (one tablespoon) of water. Is that ok?

As for Dr. Christopers Eyebright i'd like to try...there is powder extract with wich i can't be sure i'm not getting to much of something as powder can't be mixed proberpy. Herbal extract would mix nicely but contains grain alcohol, so i'm a bit worried about putting that in my eye. And again it reccomended 3-6 drops in an eyecup, and i have not been able to found out how much an average eyecup holds, should it be fulled to the brim, etc. Doesn't seem to be strandarized.

Zhank you.