THE NEGATIVE ERG IS NOT SYNONYMOUS WITH NIGHTBLINDNESS

Purpose: To provide electroretinographic differentiation between 4 genetically distinct conditions associated with a neg- ative, Schubert-Bornschein type electroretinogram (ERG): Complete congenital stationary night blindness (cCSNB), incomplete CSNB (incCSNB), Duchenne muscular dystrophy, and a family with an autosomal dominantly inherited neg- ative ERG. Methods: ERGs were recorded in all subjects according to the ISCEV standards. Additionally, a long-duration flash was used under photopic testing conditions to separate depolarizing (ON) and hyperpolarizing (OFF) bipolar cell contribu- tions. Dark adaptometry was obtained in cooperative adult subjects. Results: We were unable to differentiate between these 4 genetically distinct conditions using the scotopic ERG response to the bright white flash only. The photopic, cone-derived ERG to both short- and long-duration flashes was more informative in making distinctions between these 4 disorders and understanding the possible mechanisms behind the abnormal ERG. Conclusion: None of these disorders are progressive or a result of abnormal photoreceptor phototransduction. We sug- gest that they each represent a signal transmission error at the photoreceptor to depolarizing bipolar cell synapse that affects both rod and cone output. We propose that vision is spared in the latter 2 conditions because of timing errors in transmission as opposed to a complete signaling block, as seen in cCSNB.