Congenital stationary night blindness (CSNB) is found mainly in the Appaloosa, and it is inherited as a recessive trait. Cases are also noted in Thoroughbreds, Paso Finos, and Standardbreds. CSNB appears to be caused by a failure of neurotransmission in the middle retina. Clinical signs include visual impairment in the dark with generally normal vision in daylight. There is behavioral uneasiness and unpredictability at night. CSNB does not generally progress, hence its name, but horses with progression to vision difficulties in the daytime have been noted. An ophthalmoscopic examination of horses with CSNB will look normal to the veterinarian's eyes. Diagnosis is by clinical signs, breed type, and electroretinogram (ERG). The ERG is a test of retinal function commonly performed by veterinary ophthalmologists. There is no therapy for this condition, but affected animals should not be bred because the condition is heritable. Keeping horses stalled at night with a light on and avoiding exercise in the dark can help the horse feel more comfortable.
Taken from * By Dennis E. Brooks, DVM, PhD, Dipl. ACVO<http://www.thehorse.com/authors/140/dennis-e-brooks-dvm-phd-dipl-acvo>
* Dec 1, 2002