dalmation gone blind over night, well a few weeks

the vet has put it down to an "inflamation in the optical chiasma that has
stopped the signal from the eyes to the brain". apparenetly the eyes are
perfect (were perfect, the retina is now dieing through lack of use) no
disease nothing but she had just gone blind! looking back it started just
around Christmas 2002 but didnt notice it until 2 months ago. i just didnt
think she would go blind as she isnt even 9 yet!! i have been looking at all
sorts of theories but none have come through?! one question i have could
myxematosis play a part in her blindness?? because she has always been prone
to eat rabbit c**p! or could some weed killer that has been put on the weeds
which the rabbit ate & then c****ed and then my dog ate cause the
blindness? or am i looking for something i will never find the answer to?
Many thanks for your time