I'd try changing food and litter just in case there is an allergic component to this maybe?
I'd also try a vet ophthalmologist...taking all the results you have from your vet to them... like us humans sometimes we need a specialist when it is a case outside the "normal" culprits :-(
I'd also try a vet ophthalmologist...taking all the results you have from your vet to them... like us humans sometimes we need a specialist when it is a case outside the "normal" culprits :-(