Congenital stationary night blindness (CSNB) is a group of non-progressive retinal disorders characterized by an abnormal dark-adaptation curve, poor visual acuity, nystagmus, myopia (ranging from low to high), strabismus, and fundus abnormalities. There are two forms of CSNB, complete (CSNB1) and incomplete (CSNB2), according to the degree of rod function, measured by dark adaptometry or electroretinogram (ERG). The b-wave responses in patients with CSNB1C are severely deficient, but the a-waves are normal.
CSNB can be inherited as X linked recessive, autosomal recessive, or autosomal dominant patterns. Autosomal recessive congenital stationary night blindness is rare disease. However, the prevalence is unknown.
Al Oreany et al., (2016) described 20-year-old twin brothers with congenital stationary night blindness (CSNB). Both brothers presented with small amplitude pendular horizontal nystagmus, high myopia, hypoplastic titled discs and negative full field ERG with no measurable rod response. Next-generation sequencing identified a homozygous 1-bp deletion in exon 18 of the TRPM1 gene in both brothers. The parents were consanguineous and were both heterozygous carriers for the mutation.