An eight-year-old male castrated mixed breed dog presented to the University of Pennsylvania Ophthalmology service for evaluation of acute vision loss. Over the past few months the owners observed the patient having trouble locating treats on the floor and becoming hesitant to jump off the furniture. Approximately 24 hours prior to presentation, the patient was picked up from a boarding facility. Upon arriving home, the owners noticed he was having trouble navigating around the house, was bumping into furniture and seemed completely unaware of his surroundings. Ophthalmic examination revealed a negative menace response OD and inconsistent response OS. Pupillary light reflex (PLR) was present, but significantly decreased OU and the dazzle reflex was inconsistent OU. Both pupils were dilated in the ambient lighting of the exam room. Indirect ophthalmoscopy showed mild retinal vessel attenuation and altered tapetal reflectivity peripherally OU. A colorimetric pupillary reflex device, the Melan-100 testing unit, was used to help differentiate if the cause of blindness was due to a retinopathy or a post-retinal disease. When stimulated with a high intensity wavelength of blue light, the patient showed a strong PLR and dazzle reflex, while the high intensity red light did not stimulate a PLR or dazzle reflex. This eliminated central (post-retinal) causes from the differential list and the acute blindness was tentatively attributed to sudden acquired retinal degeneration syndrome.