INCREASED PHASE-LAG OF THE FUNDAMENTAL HARMONIC COMPONENT OF THE 30-HZ FLICKER ERG IN SCHUBERT-BORNSCHEIN-COMPLETE-TYPE-CSNB

The 30 Hz flicker electroretinogram (ERG) response was studied in seve n patients with Schubert-Bornschein complete-type congenital stationar y night blindness (SB-CSNB) by measuring conventional peak implicit ti mes and by harmonic analysis. Responses were elicited with xenon photo strobe flashes. The fundamental flicker component showed a significant increased phase lag (P = 0.002), even though the peak implicit times were not delayed (P = 0.22). Although others have noted a ''squared-of f'' flicker waveform in SB-CSNB, this is the first quantitative demons tration of a temporal abnormality in the flicker ERG and is the first report that a retinal disease can delay the fundamental flicker harmon ic while the peak implicit time remains normal. Similarly, the phase o f the flicker fundamental harmonic in monkey was also delayed after in travitreal 2-amino-4-phosphonobutyric acid (APE) that blocks the activ ity of depolarizing bipolar cells (DEC), whereas peak implicit time re mained virtually unchanged. These observations, coupled with the norma l amplitude and slope of the photopic a-wave (which was recorded under conditions that elicit a substantial contribution from hyperpolarizin g bipolar cells) supports the hypothesis that the abnormality in the D EC pathway in SB-CSNB lies post-synaptic to the cones and not in the p resynaptic glutamate release by cone photoreceptors. (C) 1997 Elsevier Science Ltd.