The negative ERG is not synonymous with nightblindness.

PURPOSE: To provide electroretinographic differentiation between 4 genetically distinct conditions associated with a negative. 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 negative 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 contributions. 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 suggest 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.