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Congenital Stationary Night Blindness (CSNB) Overview

Congenital stationary night blindness, also known as CSNB, is a rare inherited eye condition that affects people assigned male at birth. It is characterized by impaired night vision, which can range from mild to severe.

Key Features of CSNB:

• Non-progressive: CSNB does not worsen over time.
• Night blindness: People with CSNB have difficulty seeing and distinguishing objects in low light or dark conditions.
• Reduced visual acuity: Affected individuals may experience reduced sharpness of vision, ranging from 20/30 to 20/200.
• Myopia: Many people with CSNB develop nearsightedness, which can range from mild to severe.
• Nystagmus and strabismus: Some individuals may experience involuntary eye movements (nystagmus) or crossed eyes (strabismus).
• Normal color vision: Color perception is typically unaffected.

Types of CSNB:

CSNB can be classified into two types based on electroretinographic findings:

1. Riggs type: Characterized by reduced a- and b-waves in response to a scotopic bright flash.
2. Schubert–Bornschein (S–B) type: Marked by selective loss of the b-wave.

References:

• [1] CSNB is recognized as a rare, inherited eye condition that primarily affects people assigned male at birth.
• [2] The condition is characterized by impaired night vision and reduced visual acuity.
• [3] Myopia, nystagmus, and strabismus are common features of CSNB.
• [4] Color vision is typically unaffected in individuals with CSNB.

Common Signs and Symptoms of Congenital Stationary Night Blindness (CSNB)

Patients with CSNB may experience a range of vision problems, including:

• Poor night or dim-light vision: This is often the primary symptom of CSNB, making it difficult for patients to see in low light conditions [1].
• Loss of sharpness (reduced visual acuity): Patients may have trouble seeing details and recognizing faces, even in good lighting [2][3][4].
• Nearsightedness (myopia): Many people with CSNB are nearsighted, meaning they can see close objects clearly but struggle to see distant ones [2][7].
• Increased sensitivity to light (photophobia): Some patients may experience discomfort or pain when exposed to bright lights [3][7].
• Severe nearsightedness: In some cases, CSNB can lead to severe nearsightedness, making it difficult for patients to see anything clearly [4].

It's worth noting that these symptoms are often subjective and may not be immediately apparent. A comprehensive eye examination is necessary to diagnose CSNB.

References: [1] - Signs & Symptoms of Congenital Stationary Night Blindness (CSNB) [2] - Jan 1, 2014 — They also often have other vision problems, including loss of sharpness (reduced acuity), nearsightedness (myopia ), involuntary movements of ... [3] - Jun 21, 2024 — They also have other vision problems, including increased sensitivity to light (photophobia), loss of sharpness (reduced visual acuity), severe ... [4] - People with this condition typically experience night blindness and other vision problems, including loss of sharpness (reduced visual acuity), severe ... [7] - They also have other

Diagnostic Tests for Congenital Stationary Night Blindness

Congenital stationary night blindness (CSNB) can be definitively diagnosed through various tests, which are essential in confirming the condition and ruling out other eye-related disorders. Here are some diagnostic tests used to diagnose CSNB:

• Dark-adapted electroretinography (ERG): This test is conducted by a veterinary ophthalmologist and measures the function of the retina in low light conditions [8]. It is considered definitive for diagnosing CSNB.
• Full-field electroretinograms (ERG): These tests measure the electrical activity of the retina and are used to diagnose rod system dysfunction, which is characteristic of CSNB [4].
• Genetic testing: Genetic testing can identify the specific genetic cause of CSNB, which is essential for diagnosis and family planning.
• Visual field examination: This test assesses the visual field and can help identify any impairments in vision.
• Fundoscopic examination: A fundoscopic examination allows ophthalmologists to examine the retina and choroid for any abnormalities.
• Slit-lamp examination: A slit-lamp examination is used to examine the anterior segment of the eye, including the cornea, iris, and lens.

These diagnostic tests are essential in confirming a diagnosis of CSNB and ruling out other eye-related disorders. Early detection and diagnosis can help provide appropriate management and care for individuals with CSNB.

References:

• [4] Congenital stationary night blindness (CSNB) is a group of genetically determined, largely non-progressive retinal disorders characterised by rod system dysfunction.
• [8] CSNB is definitively diagnosed by a dark-adapted electroretinography (ERG) test conducted by a veterinary ophthalmologist.
• [13] Diagnosis often occurs through the use of various tests including a electroretinogram to reveal any impairment in the retina "as a whole".

Current Drug Treatments for Congenital Stationary Night Blindness

While there is no known cure for congenital stationary night blindness (CSNB), researchers have been exploring various treatment options to alleviate its symptoms. Here are some current drug treatments being investigated:

• Metoprolol, Bromocriptine, and Tamsulosin: A study published in 2019 found that pretreatment with a combination of these medications rescued the retina in all genetic backgrounds, starting at doses of 0.2 mg/kg metoprolol, 0.02 mg/kg bromocriptine, and 0.01 mg/kg tamsulosin [5].
• Gene Therapy: Gene therapy has shown promise in treating CSNB by targeting the underlying genetic cause of the condition. For example, a study published in 2022 found that gene therapy rapidly improved night vision in adults with congenital blindness [3].
• Vitamin A: Vitamin A can treat both genetic and acquired night blindness. While it may not specifically target CSNB, it could potentially alleviate some symptoms associated with the condition [7].

Important Note

It's essential to note that these treatments are still being researched and may not be widely available or approved for use in all cases of CSNB. Additionally, more research is needed to fully understand their efficacy and potential side effects.

References:

[3] Gene therapy rapidly improves night vision in adults with congenital blindness, Penn study finds (2022) [5] Pretreatment with metoprolol + bromocriptine + tamsulosin rescued the retina in all genetic backgrounds (2019) [7] Vitamin A can treat both genetic and acquired night blindness (2023)

Differential Diagnosis of Congenital Stationary Night Blindness

Congenital stationary night blindness (CSNB) can be challenging to diagnose, and it's essential to consider other conditions that may present with similar symptoms. Here are some differential diagnoses for CSNB:

• Cone-rod dystrophy: This is a progressive retinal disorder that can cause night blindness, but unlike CSNB, it affects both cone and rod photoreceptors. Early cone-rod dystrophy may share a similar appearance with CSNB, but it has a more severe clinical course [14].
• Other retinal disorders: Conditions like Leber congenital amaurosis, retinitis pigmentosa, and cone monochromacy can also present with night blindness. However, these conditions typically have distinct clinical features that differentiate them from CSNB.
• Optic nerve hypoplasia: This is a rare condition where the optic nerve is underdeveloped, leading to vision loss, including night blindness.

Key differences between CSNB and other retinal disorders

When differentiating CSNB from other retinal disorders, it's essential to consider the following:

• Progression of symptoms: Unlike CSNB, cone-rod dystrophy and other progressive retinal disorders typically show a worsening of symptoms over time.
• Visual acuity: While CSNB is characterized by reduced visual acuity, other conditions like Leber congenital amaurosis may present with more severe vision loss.
• Fundus examination: The fundus examination can help differentiate CSNB from other retinal disorders. For example, cone-rod dystrophy often shows a characteristic "salt and pepper" appearance.

Genetic testing

In some cases, genetic testing may be necessary to confirm the diagnosis of CSNB or rule out other conditions. This is particularly important when considering differential diagnoses like cone-rod dystrophy.

References:

[14] Congenital stationary night blindness (CNSB) is a clinically and genetic diverse group of nonprogressive retinal disorders that is characterized by stable poor vision in low light (night blindness).