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Night Blindness, Congenital Stationary
Night blindness is a feature of many pigmentary and other retinal disorders, most of which are progressive. However, there is also a group of genetically heterogeneous disorders, with generally stable scotopic defects and without RPE changes, known as congenital stationary night blindness (CSNB). At least 9 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them. All are caused by defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves. The photopic ERG is usually abnormal to some degree as well and visual acuity may be subnormal. In the pregenomic era, subtleties of ERG responses were frequently used in an attempt to distinguish different forms of CSNB. Genotyping now enables classification with unprecedented precision.
The night blindness is usually nonprogressive as the name implies.
No systemic disease is associated with congenital stationary night blindness.
This recently reported type of congenital stationary night blindness has not yet been further classified. It is inherited in an autosomal recessive pattern resulting from homozygous mutations in GRP179. The gene encodes an orphan G protein receptor whose function is as yet unknown.
No treatment beyond correction of the refractive error is available but tinted lenses are sometimes used to enhance vision.