Hiya

I get this on His Nibs' eyes - one is worse than the other - and the vet said much the same as yours.

I actually went to my local pet shop (not a chain one) and spoke to them about it and they recommended a special cat eye drop thing (like an Optrex but for cats) - it wasnt expensive and was really good, you can drop it into the eye, or put on a tissue and wipe over the closed eye

e