Congenital stationary night blindness (CSNB) is a rare inherited eye disease affecting dogs. CSNB causes slowly progressive degeneration of the Retina, which is the part of the eye that collects visual information and communicates with the brain. Loss of night vision is first noticed in affected dogs as early as 5 weeks of age, while ophthalmologic changes are not visible until affected dogs are 2-3 years of age. Light brown patches form on the surface of the retina. These patches increase in size and coalesce over time until the entire retina is affected. Affected dogs may be reluctant to move in low light and over time, day vision is also lost.