Children with complete or incomplete congenital stationary night blindness: ophthalmological findings, standard ERGs and ON-OFF ERGs for differentiation between types

Purpose: Congenital stationary night blindness (CSNB) is a group of retinal disorders with diverse clinical characteristics. The most common types are complete and incomplete CSNB. Both can have normal fundus appearance and an electronegative waveform of the electroretinogram (ERG). Our aim was to define ERG differences between complete and incomplete CSNB in a pediatric population. Subjects and methods: In 12 children (5-18 years old) with clinical signs of stationary night blindness, standard full-field ERGs and ON-OFF ERGs were recorded. These were abnormal if the implicit time was above 95 % of the upper confidence limit and the amplitude below 5 % of the lower confidence limit of the normative data. Comparisons between the data were performe with Mann-Whitney U tests, with p < 0.01 considered as significant. Results: According to the ERG characteristics, complete CSNB was diagnosed in 8 of the children, and incomplete CSNB in the remaining 4 children. Dark-adapted ERGs showed negative waveforms of the combined rod-cone response in all 12 children, with normal a-waves and reduced b-waves, which indicated post-photoreceptor dysfunction. No rod response was detectable in the children with complete CSNB, with reduced rod response in those with incomplete CSNB. Light-adapted ERGs showed normal or subnormal amplitudes of the cone response and the 30-Hz flicker response in complete CSNB, where the cone response a-waves were also distinctly broadened. In the children with incomplete CSNB, the light-adapted ERGs were significantly reduced. In complete CSNB, the ON-OFF ERGs showed alterations of only the ON-response component (ON-bipolar cell dysfunction), while in incomplete CSNB, both the ON- and OFF-responses were reduced (ON- and OFF-bipolar cell dysfunction). Comparisons of the ERG amplitudes between the children with complete and incomplete CSNB demonstrated significant differences in rod responses, cone responses, 30-Hz flicker responses, and OFFresponses. Conclusion: Distinct electrophysiological characteristics can be used to differentiate between complete and incomplete CSNB. Moreover, ONOFF ERGs are important for precise localization of the retinal bipolar cell dysfunction, and these can also be reliably recorded in children.