Our terrier, a Westie, suffers from "dry eye". this causes a lot of mucus to form in the eye.
We use prescription eye treatment every morning and night, but he still ejects some mucus at the nose, each side, every day. It really shows on his white fur.
The vet says the eye treatment should prevent dry eye from causing blindness. That would be especially tough as he is already deaf.
A fellow BT Mom! :)
It could just be a cataract, like your vet said. If he did injure his eye (which is so easy for these guys to do), blood vessels will grow across the eyeball to try to heal the eye from the inside. That could be the squiggle you're seeing. If you're worried he has an eye injury/ulcer, your vet can stain the eye to check for damage. If that's the case, he'll probably just need some prescription eye drops. Good luck!