Night Blindness, Congenital Stationary, CSNB1H
Patient Information
Characteristics
Background and History
Various conditions causing poor night vision, sometimes called night blindness, have been known for centuries. Many disorders of the retina cause night blindness and most of these are progressive and associated with other ocular disease. However, several conditions causing difficulties with night vision are not progressive nor are they part of other syndromes. These are generally referred to as congenital stationary night blindness (CSNB). This condition, CSNB1H, closely resembles the other 9 types.
Clinical Correlations
Night blindness has been detected in young children who have difficulty seeing in dim light. It may be present at birth. Daytime vision is near normal in young people but by midlife there may be mild difficulties with color perception and increased discomfort in brightly lit environments. In most patients there is also loss of peripheral vision called visual field constriction which in advanced cases results in tunnel vision.
Aside from the night blindness, patients are otherwise healthy.
Genetics
Inheritance
This is an autosomal recessive disorder requiring mutations (DNA changes) in both members of a specific gene pair. Carriers of a single change (e.g. parents) do not experience symptoms but when two such carriers have children they can expect that 1 in 4 (25%) will have this form of night blindness.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Difficulty seeing at night is the primary symptom and is generally evaluated with a special electrical test called an electroretinogram (ERG). The exact type of night blindness (there are numerous retinal conditions in which this is a symptom) has to be determined by DNA testing. An ophthalmologist (medical eye doctor) likely will arrange for these tests. He or she may also order a visual field test to confirm the loss of the peripheral field of vision.
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