A border collie was evaluated by the Cornell University Hospital for Animals Ophthalmology Service because of a sudden onset of apparent complete loss of vision. Signalment: The border collie was a three year old 17 kg (37.5-lb) spayed female. History: The dog, which resided on a farm in upstate New York with 17 other border collies, had been obtained as a rescue approximately two years ago. In that time she had experienced no medical problems and had not traveled out of New York State. She had traveled to an area south of Albany (Saugerties) known to harbor Lyme disease (Borreliosis); her owner and three other dogs reportedly had been treated for Lyme disease recently. The dog's medical, travel and reproductive history prior to her acquisition by her present owner was unknown. She was up to date on vaccinations against rabies, distemper, canine adenovirus 2, parvovirus and panleukopenia. On the afternoon of presentation the dog was found by her owner to be exhibiting signs of acute vision loss. She was running into objects and was unable to catch treats thrown by her owner, a feat she had previously been able to accomplish. According to her owner, her pupils were dilated and she acted lethargic. Her owner therefore brought her immediately to the Ophthalmology Service of Cornell University.