Congenital stationary night blindness

A genetic disorder affecting night vision

Congenital stationary night blindness
Synonyms	CSNB
Pronounce	/ˌkɒn.dʒəˈnɪ.təl ˈsteɪ.ʃə.ner.i ˈnaɪt ˌblaɪnd.nəs/
Field	Ophthalmology, Genetics
Symptoms	Difficulty seeing in low light or darkness, nystagmus, reduced visual acuity
Complications	Impaired night vision, educational or occupational limitations
Onset	Birth or early infancy
Duration	Lifelong
Types	Complete (type 1), Incomplete (type 2)
Causes	Genetic mutations (e.g., in the NYX, GRM6, TRPM1, or CACNA1F genes)
Risks	Family history of CSNB or consanguineous parents
Diagnosis	Electroretinography (ERG), genetic testing, clinical examination
Differential diagnosis	Retinitis pigmentosa, vitamin A deficiency, other forms of night blindness
Prevention	None
Treatment	Supportive; visual aids and low-vision services
Medication	None specific; vitamin A not effective
Prognosis	Stable; non-progressive with relatively good daytime vision
Frequency	Rare; estimated 1 in 100,000–1,000,000
Deaths	Not life-threatening

Figure 1. Schematic structure of Ca_V1.4 with the domains and subunits labeled.

Congenital stationary night blindness (CSNB) is a group of rare, non-progressive genetic disorders that primarily affect an individual's ability to see in low-light conditions. This condition is present from birth and remains stable throughout life, distinguishing it from other forms of night blindness that may worsen over time.

Pathophysiology

CSNB is caused by mutations in genes that are crucial for the normal functioning of the retina, the light-sensitive layer of tissue at the back of the eye. These mutations disrupt the normal transmission of visual signals from the photoreceptor cells to the bipolar cells in the retina, leading to impaired night vision. The condition is typically inherited in an X-linked, autosomal dominant, or autosomal recessive manner, depending on the specific genetic mutation involved.

Types

There are several types of CSNB, which are classified based on the genetic mutations and the specific retinal pathways affected:

• CSNB1: Also known as complete CSNB, this type is characterized by a lack of rod function, leading to severe night blindness. It is often associated with mutations in the NYX gene.

• CSNB2: Known as incomplete CSNB, this type involves partial rod function and is often linked to mutations in the CACNA1F gene. Individuals with CSNB2 may have better night vision than those with CSNB1.

• Oguchi disease: A rare form of CSNB characterized by a unique golden or grayish discoloration of the retina, which disappears after prolonged dark adaptation.

Symptoms

The primary symptom of CSNB is difficulty seeing in low-light or dark environments, a condition known as nyctalopia. Other symptoms may include:

• Reduced visual acuity
• Nystagmus, or involuntary eye movements
• Myopia, or nearsightedness
• Strabismus, or misalignment of the eyes

Diagnosis

Diagnosis of CSNB typically involves a combination of clinical evaluation, family history, and specialized tests such as:

• Electroretinography (ERG): This test measures the electrical responses of the retina to light stimuli and can help differentiate between complete and incomplete forms of CSNB.
• Genetic testing: Identifying specific genetic mutations can confirm the diagnosis and help determine the inheritance pattern.

Management

There is currently no cure for CSNB, and management focuses on optimizing visual function and quality of life. Strategies may include:

• Use of low-vision aids and adaptive devices
• Regular monitoring by an ophthalmologist
• Genetic counseling for affected individuals and their families

Prognosis

The prognosis for individuals with CSNB is generally good, as the condition is non-progressive and does not lead to complete blindness. However, the degree of visual impairment can vary, and some individuals may experience significant challenges in low-light environments.

Related pages

• Night blindness
• Retinitis pigmentosa
• Genetic disorders
• Electroretinography

External links

• GeneReview/NCBI/NIH/UW entry on X-Linked Congenital Stationary Night Blindness