Congenital stationary night blindness with hypoplastic discs, negative electroretinogram and thinning of the inner nuclear layer

Abstract

Purpose: To describe congenital stationary night blindness (CSNB) with negative electroretinogram, hypoplastic discs, nystagmus and thinning of the inner nuclear layer (INL). Methods: Retinal structure was analyzed qualitatively with spectral domain optical coherence tomography and wide field imaging. Retinal function was evaluated with full-field electroretinography (ffERG). Molecular genetic testing included next-generation sequencing (NGS) of the known genes involved in CSNB. Results: Patients presented with CSNB presented with nystagmus, high myopia, hypoplastic discs and negative ffERG with no measurable rod response. The retinas appeared normal and automated segmentation of retinal layers demonstrated a relative reduction of thickness of the INL. There was no significant change in the ffERG after prolonged 2 hour dark adaptation compared to standard 30 minute dark adaptation. Affected family members harboured the homozygous 1-bp deletion c.2394delC in exon 18 of the TRPM1 gene, whereas their unaffected parents were heterozygous carriers. Conclusions: This data expands the genotype and phenotype spectrum of CSNB. The lack of improvement of rod responses after prolonged dark adaptation, together with thinning of the INL, is compatible with postreceptoral transmission dysfunction in the bipolar cells. Such knowledge may prove useful in future development of treatment for outer retinal dystrophies, using opsin genes to restore light responses in survivor neurons in the inner retina.