Congenital stationary night blindness (CSNB) is a rare non-progressive retinal disorder. People with CSNB often have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients may also have reduced visual acuity, myopia, nystagmus, and strabismus. CSNB has two forms -- complete, also known as type-1 (CSNB1), and incomplete, also known as type-2 (CSNB2), which are distinguished by the involvement of different retinal pathways. In CSNB1, downstream neurons called  bipolar cells are unable to detect neurotransmission from photoreceptor cells. CSNB1 can be caused by mutations in various genes involved in neurotransmitter detection, including NYX. In CSNB2, the photoreceptors themselves have impaired neurotransmission function; this is caused primarily by mutations in the gene CACNA1F, which encodes a voltage-gated calcium channel important for neurotransmitter release. CSNB has been identified in horses and dogs as the result of mutations in  TRPM1 (Horse, "LP"), GRM6 (Horse, "CSNB2"), and LRIT3 (Dog, CSNB). Congenital stationary night blindness (CSNB) can be inherited in an X-linked, autosomal dominant, or autosomal recessive pattern, depending on the genes involved. Two forms of CSNB can also affect horses, one linked to the leopard complex of equine coat colors and the other found in certain horse breeds. Both are autosomal recessives. Symptoms and signs
The X-linked varieties of congenital stationary night blindness (CSNB) can be differentiated from the autosomal forms by the presence of myopia, which is typically absent in the autosomal forms. Patients with CSNB often have impaired night vision, myopia, reduced visual acuity, strabismus and nystagmus.
These markers include angiotensin-converting enzyme, cathepsin S, chitotriosidase, and CCL18 in the blood plasma; and tumor necrosis factor alpha in splenic Gaucher cells (engorged macrophages). Diagnosis
Gaucher disease is suggested based on the overall clinical picture. Initial laboratory testing may include enzyme testing. As a result, lower than 15% of mean normal activity is considered to be diagnostic. Decreased enzyme levels will often be confirmed by genetic testing. Numerous different mutations occur; sequencing of the beta-glucosidase gene is sometimes necessary to confirm the diagnosis. Prenatal diagnosis is available and is useful when a known genetic risk factor is present.A diagnosis can also be implied by biochemical abnormalities such as high alkaline phosphatase, angiotensin-converting enzyme, and immunoglobulin levels, or by cell analysis showing "crinkled paper" cytoplasm and glycolipid-laden macrophages.Some lysosomal enzymes are elevated, including tartrate-resistant acid phosphatase, hexosaminidase, and a human chitinase, chitotriosidase. This latter enzyme has proved to be very useful for monitoring Gauchers disease activity in response to treatment, and may reflect the severity of the disease

Classification
Gauchers disease (GD) has three common clinical subtypes. These subtypes have come under some criticism for not taking account of the full spectrum of observable symptoms (the phenotypes). Also, compound heterozygous variations occur which considerably increase the complexity of predicting disease course. GD type I (non-neuropathic) is the most common and least severe form of the disease. Symptoms may begin early in life or in adulthood and mainly affect the liver, spleen, and bone.