Equine veterinarians know congenital stationary night blindness (CSNB) to be an inherited, non-progressive disease found mainly in Appaloosa horses. Horses with this condition remain healthy and useful, showing normal eyesight during daylight, but reduced sight after dark. There is no known treatment at this time, reports the Horsetalk website.
Although CSNB also has been seen in Thoroughbreds, Paso Finos and Standardbreds, scientists found that the incomplete gene that causes the spotted coat pattern in the Appaloosa horse also decreases a particular protein in the eye that controls the calcium concentration in eye fluid. Published in the "Genetics" journal in 2008, this study surmises that increased calcium alters cell signals in the horse's eye, causing the condition.
Horses with CSNB suffer varying abilities to see at night, ranging from reduced vision in dim light to complete blindness. They may show confusion and apprehension in low light and injure themselves. They may squint and display an involuntary movement of the eyeballs called nystagmus, veterinarian Lynne Sandmeyer and colleagues at the University of Saskatchewan reported in "Veterinary Ophthalmology" in 2007, according to the Horsetalk website.
The "Appaloosa Journal" recommends establishing consistent patterns with your horse by using your touch and voice to announce your presence after dark. Bright lighting in a stall or paddock area and safe fencing can also protect your horse from injury.