I am So sorry to hear of your Jack Russell's recent serious illness. I, too, have a Jack Russell and mine also has cataracts, retinal degeneration and other signs of aging. So... I can relate! Regardless, I would be concerned that your pup more than likely has a primary brain disorder, and, due to her age and the age of onset of symptoms, a tumor in the brain would not surprise me. As a veterinarian, I would not discourage a pet owner from seeking answers to what the underlying problem in their pet is, if they are willing and able to pursue the answers/ diagnosis, Age, in your case, age is not what would keep me from recommending further testing. My Jack Russell is a spry 15 years old... and she could live a few more wonderful years. your vet's responsibility is to give you their best opinion of what may be going on based on the clinical picture and to educate you, give you ALL options, and allow you to make educated decisions for yourself. If your vet decided you should not pursue visiting with a neurologist to pursue further diagnosis - that is not fair. If, perhaps, you have agreed, based on the education you received from your vet, it is fine not to pursue a diagnosis. Treating the symptoms is super , but you may help her more by understanding the problem better and treating the underlying issue, if possible. ok, well, it's my soap box, and I'll get off now and answer your question. It sounds to me as if she likely has blindness and poor balance due to the same underlying cause. It is not likely that her balance issue has anything to do with her eyes themselves. if your vet has not done so already, see it they will agree to a trial on corticosteroids to see if she responds. if so, a brain tumor would be more likely than parasitic disease. A CT scan or MRI of her brain will likely give you important pieces to the puzzle. I wish you and your girl the best.