Your vet will have to run a series of diagnostics to determine the cause of the blindness. My first thought was a mass pressing on the optic nerve or a mass in the section of the brain that controls sight. If it's meningitis, while the sight may not be able to be restored (I don't know what the odds of that are), the meningitis can be dealt with medically and the dog can be restored to health, if not sighted. If it's a mass, however, that is much more sinister and at that point you would need to discuss with your vet the type of mass it is, what its potential for growth is or how quickly it will grow, and what else it can affect before you can decide what to do about it from there. My heart goes out to you. This is a scary thing to deal with, what with so many unknowns. Please keep us posted as to what your vet tells you. You are in my thoughts.
Ghilly
Something I had not thought of when I wrote my first response is that it could also be caused by a couple of other things. Firstly, did the vet take your dog's blood pressure when he examined her? High blood pressure can cause sudden vision loss. Also, Pekingese are prone to something called PRA, or progressive retinal atrophy. The dog appears to be normal until the sight is completely gone. Her vision could have been declining for a long time and it was not until it went completely that you realized there was a problem, hence making you think that it was something that happened suddenly. Just something to think about. It could also be caused by optic neuritis. There are two types of optic neuritis that affect dogs, but the more common one can be caused by a neoplasm (growth) on the optic nerve, or it can be caused by a parasitic disease such as toxoplasmosis. It can also be idiopathic, meaning it comes from an unknown cause, seemingly occurring out of the blue.
After I thought about it, I realized my first response to you sounded very dismal and made it sound like it was a simple "black and white" thing and I wanted to re-post and let you know that, while it is still a serious thing, it may not be as serious as my original response would have led you to think.
Again, though, please let us know what your vet says after he has had the chance to run some diagnostics.
Ghyllie
Thanks for your information. MY pekingese seems to have his sight coming back. The scan he had showed no tumour or menengitis. My vet has told me to keep him on his steroids for another couple of weeks to see how things go.