Vision in dogs depends on two main types of retinal cells: rods, which are responsible for vision in dim light (night vision), and cones, which are responsible for color and daylight vision. In CSNB, the function of rod cells is disrupted due to a genetic mutation affecting retinal signal transmission. As a result, affected dogs struggle to see in low-light environments, even though their daytime vision may appear normal.
CSNB is considered a non-progressive congenital disorder, meaning the condition is present from birth and typically does not worsen over time. Unlike degenerative eye diseases, the structural components of the eye may appear normal, but the electrical signaling pathway between the retina and brain is impaired.
Clinical signs of CSNB are often subtle in well-lit environments but become more noticeable in dim lighting or darkness. Affected dogs may show hesitation when moving in poorly lit areas, reluctance to go outside at night, or difficulty navigating in dark rooms. They may bump into objects in low-light conditions but behave normally during the day.
Because daylight vision is usually unaffected, CSNB can sometimes go unnoticed without specific testing. Owners may only observe behavioral differences in nighttime or shaded environments, which can delay diagnosis.
The CSNB eye evaluation and diagnostic testing often includes both clinical examination and specialized retinal function testing. A veterinary ophthalmologist may perform a standard eye exam using a slit-lamp biomicroscope and indirect ophthalmoscope to rule out structural abnormalities. However, because CSNB is primarily a functional disorder, more advanced testing such as electroretinography (ERG) is often required.
ERG measures the electrical responses of retinal cells to light stimulation. In dogs affected by CSNB, rod cell responses are significantly reduced or absent, confirming impaired night vision function. This makes ERG a key diagnostic tool for accurately identifying the condition.
In addition to clinical testing, DNA testing for the specific genetic mutation associated with CSNB is used in some breeds. This helps identify clear, carrier, and affected dogs before clinical signs are observed, allowing breeders to make informed breeding decisions.
Results are generally reported as:
- Clear (Normal): No mutation detected and normal retinal function.
- Carrier: One copy of the mutation; no clinical signs but can pass the gene to offspring.
- Affected: Two copies of the mutation and/or confirmed night vision impairment on ERG testing.
CSNB is especially important in breeding programs, as early genetic screening helps prevent the spread of inherited vision disorders while maintaining healthy genetic diversity. Avoiding carrier-to-carrier breeding significantly reduces the risk of producing affected puppies.
For dog owners, CSNB diagnosis helps explain behavioral patterns in low-light conditions and allows for appropriate lifestyle adjustments. While there is no cure for congenital night blindness, affected dogs typically adapt well to well-lit environments and can live normal, active lives with minor environmental modifications.
The Congenital Sensory Night Blindness (CSNB) Health Test is a valuable genetic and ophthalmic screening tool that supports early detection of inherited vision disorders, improves breeding decisions, and helps ensure long-term ocular health and quality of life in dogs.
