Thanks for all your messages everyone!
Tia is almost 8 years old, and is solid black apart from a white spot on her chest and a few grey hairs on her face and ears.
We had intended to get a cocker that needed rehoming, and so didn't expect perfection. One of her eyes will be fine, but the other most likely won't be. We have 3 months of medication, and then re-assess - time will tell.
Cheers,