Night Blindness, Congenital Stationary, CSNB1H

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 10 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them.  All are caused by defects in visual signal transduction within rod photoreceptors or in defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves.  However, the photopic ERG can be 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.

Night blindness in this condition can be detected in early childhood and may be congenital.   Photophobia, reduced cone sensitivity. and mild dyschromatopsia may develop in midlife.  Peripheral field constriction can be demonstrated.  Visual acuity is near normal and there is no nystagmus or high myopia as reported for some other forms of CSNB.