Congenital stationary night blindness

Congenital stationary night blindness (CSNB) is a group of inherited retinal disorders characterized by impaired vision in low-light conditions (night blindness or nyctalopia) that is present from birth and remains stable (non-progressive) throughout life. The condition affects the retina, specifically the function of rod photoreceptors or the signal transmission from photoreceptors to bipolar cells in the retina. CSNB is sometimes also referred to as essential night blindness or hereditary stationary night blindness. Clinically, patients with CSNB typically present with difficulty seeing in dim lighting or at night from early childhood. Additional features may include reduced visual acuity, myopia (nearsightedness, which can be high-grade), nystagmus (involuntary eye movements), and strabismus (misalignment of the eyes). The fundus (back of the eye) typically appears normal on standard ophthalmoscopic examination, which distinguishes CSNB from progressive retinal dystrophies such as retinitis pigmentosa. Electroretinography (ERG) is the key diagnostic tool and reveals characteristic abnormalities. Two major electrophysiological subtypes are recognized: the complete form (Riggs type or Schubert-Bornschein complete type), in which both rod and cone signaling pathways are affected, and the incomplete form, in which rod and cone function is partially preserved but abnormal. CSNB can be caused by mutations in numerous genes, including NYX, GRM6, TRPM1, GPR179, LRIT3, RHO, GNAT1, PDE6B, GNB3, and SLC24A1, among others. Inheritance patterns vary depending on the genetic subtype and include X-linked recessive (the most common forms, associated with NYX and CACNA1F mutations), autosomal recessive, and autosomal dominant forms. There is currently no cure or specific treatment for CSNB. Management focuses on correcting refractive errors (particularly myopia) with glasses or contact lenses, addressing strabismus or nystagmus when needed, and providing low-vision aids and counseling regarding adaptation to low-light environments. The prognosis is generally favorable as the condition does not worsen over time, and most patients maintain useful daytime vision throughout life.

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