Congenital Stationary Night Blindness (CSNB)-Case Reports and Review of Current Knowledge

Purpose: To present the current state of knowledge and our diagnosed patients with congenital stationary night blindness. Material and methods: Data from the PubMed database on CSNB and the presentation of patients with complete and incomplete forms of this condition. Patients underwent routine ophthalmologic examination, optical coherence tomography, and full-field elecroretinogram (ERG-ISCEV), ON-OFF ERG. Results: CSNB is a group of rare, non-progressive retinal diseases characterized by impaired night vision from birth, reduced visual acuity, myopia, nystagmus, and strabismus. Color vision and fundus imaging are most often normal. CSNB is mainly inherited autosomal recessively. Eighteen genes with more than 360 pathogenic variants have been detected in this condition. The effect of gene mutations is to damage the function of rods (Riggs type) and bipolar cells of the retina (Schubert-Bornstein type). The key diagnostic test in CSNB is ERG. In diagnosed cases of complete CSNB the following types have been registered: rod ERG absent, rod-cone response negative (ON bipolar cell defect), and photopic ERG enlarged a-wave. In incomplete CSNB-rod ERG-subnormal, rod-cone response-negative (bipolar cell defect ON, OFF), photopic ERG-subnormal with a double peak in the flicker fusion frequency. Knowledge of the phenotypic changes associated with various gene pathogenic variants is still very limited, hindering the ability to correctly diagnose a patient based on clinical examination and additional ophthalmologic tests. However, some phenotypic features found in our cases were consistent with pathogenic variants previously described in the literature and helped to make a diagnosis that was proven by genetic testing. Conclusions: Congenital stationary night blindness should be considered in the diagnosis of retinal diseases manifesting with impaired night vision. A correct diagnosis is especially important for the patients, as it is nonprogressive, unlike other diseases that should be considered in the differential diagnoses.