Purpose: To investigate the slow and fast rod signals of the scotopic 15-Hz flicker ERG in patients with molecularly confirmed Stargardt disease type I (STGD1). There is evidence that these slow and the fast rod ERG signals can be attributed to the rod bipolar-AII cell pathway and the rod-cone coupling pathway, respectively.
Methods: Twenty-seven patients with STGD1 with mutations in both alleles of the ABCA4 gene were included. Scotopic ERG response amplitudes and phases to flicker intensities ranging from -3.37 to -0.57 log scotopic troland x sec (log scot td x sec) were measured at a flicker frequency of 15 Hz. In addition, scotopic standard ERGs were obtained. Twenty-two normal subjects served as controls.
Results: The amplitudes of both the slow and fast rod ERG signals were significantly reduced in the STGD1 group. The phases of the slow rod signals lagged significantly, whereas those of the fast rod signals did not. The standard scotopic ERG did not reveal significant alterations.
Conclusions: The results provide evidence that a defective ABCA4 transporter can functionally affect both the rod bipolar-AII cell pathway and the rod-cone coupling pathway. In STGD1, the scotopic 15-Hz flicker ERG may reveal subtle abnormalities at different sites within the rod system that remain undetected by standard ERG techniques.