Congenital Stationary Night Blindness
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Congenital stationary night blindness, or CSNB, is an inherited failure of retinal signalling in low light. Affected horses are born unable to see normally from dusk through darkness, while daylight vision is usually functional. “Stationary” means the defect does not progressively worsen, although age-related or inflammatory eye disease can develop separately.
Horses may become anxious at dusk, refuse to enter a dark stable or trailer, collide with objects, struggle to find feed and water or spook when shadows change. In a familiar environment signs can be subtle and attributed to temperament or poor training. The eye can look structurally normal.
In Appaloosas and related leopard-complex breeds, horses with two copies of the LP allele are affected. A separate recessive GRM6 variant, often called CSNB2, causes disease in Tennessee Walking Horses and is found in some related breeds. Other breeds can have night blindness from different, not yet defined causes. A genetic result must therefore be breed-appropriate.
CSNB is not painful, contagious or a cause of daytime blindness by itself. It differs from vitamin A deficiency, cataract and retinal degeneration, which can be acquired or progressive. There is no cure, but many affected horses work safely during daylight with predictable management. Breeding implications depend on the mutation: LP also produces desirable coat pattern, while mating two LP carriers can produce an affected LP/LP foal.
Daylight competence lets affected horses memorise a familiar paddock, masking the deficit until dusk, transport or a power failure. Homozygosity for leopard complex disrupts retinal signalling in Appaloosa-related horses, while another variant causes CSNB in some gaited horses. The normal external appearance of the eye distinguishes neither genotype nor functional severity.
The deficit is lifelong, painless and present from birth.
Screening & Early Detection
History focuses on behaviour from twilight to darkness, unfamiliar dim buildings and night paddocks. A veterinary ophthalmologist performs a complete examination to exclude cataract, uveitis and retinal degeneration. Definitive functional diagnosis uses dark-adapted electroretinography, which records the characteristic abnormal retinal response despite a structurally normal-looking eye.
DNA testing identifies LP copy number in Appaloosa-pattern horses and the validated CSNB2 variant in appropriate gaited breeds. Results distinguish clear, carrier and affected genotypes according to each inheritance pattern. A negative breed-specific test does not exclude CSNB caused by another gene, so clinical signs still warrant electroretinography.
Foals from at-risk matings can be tested before management problems emerge. Owners should not deliberately expose a suspected horse to obstacles in darkness as a home test. Sudden or progressive night difficulty in an adult is not typical congenital stationary disease and requires investigation for acquired ocular or neurological illness.
Electroretinography is performed after adequate dark adaptation using an age-appropriate reference response. Daylight vision is assessed separately so an additional ocular disorder is not overlooked.
Treatment & Management
No medication restores the missing low-light retinal signal. Management prevents injury by keeping the layout of paddocks, stalls, gates, feed and water consistent. Hazards, low branches and loose equipment are removed, fencing is highly visible and safe, and reliable lighting covers paths, loading areas and indoor transitions. Light changes are gradual so the horse can adapt.
Handling, transport and exercise are scheduled in daylight where possible. The horse is warned before approach and may benefit from a calm sighted companion after dark. Riding in dim light, unlit trailering and turning into an unfamiliar night paddock are avoided. Punishment for hesitation increases fear without improving vision.
Routine ophthalmic care remains important because cataract or ERU can reduce the useful daylight vision on which the horse relies. Genetic counselling prevents affected matings while preserving informed breeding choices: an affected horse transmits the relevant allele according to the specific mutation, and carriers may be bred only with tested compatible mates if the breeding programme accepts that risk. Quality of life is usually good with consistent daylight use and environmental design.
Emergency lighting has battery backup so a power outage does not suddenly make familiar housing unsafe.
