[AC and DC electroretinography in degenerative retinal diseases]

In clinical electrophysiology AC-recorded ERGs are used for the investigation of a- and b-wave parameters. The direct coupled (DC-ERG) ist used to record the c-wave. Theoretically the DC-ERG technique has less influence on the recorded potentials than the AC-ERG technique. We recorded AC- and DC-ERGs of 20 normal eyes, 17 eyes with x-linked congenital retinoschisis and 30 eyes with retinal degenerations. In normal eyes no difference was found between AC- und DC-ERG concerning a- and b-wave amplitudes, latencies and implicit times, the b/a-ratios and the oscillatory potentials. The 30 Hz flicker amplitude was higher in the DC-ERG (p less than 0.0003). The intraindividual variability of all measured parameters was comparable between AC- and DC-ERG. In x-linked retinoschisis the b-wave amplitudes and the b/a-ratios were lower in the DC-ERG than in the AC-ERG. In retinal degenerative diseases the a-wave amplitudes were higher and the dark-adapted b-wave amplitudes lower in the DC-ERG, therefore the b/a-ratio was lower in the DC-ERG. We conclude, the DC-ERG is a reproducible method for clinical routine investigations. It is comparable to the conventional AC-ERG technique. In certain diseases the pathological features of the electroretinogram were more distinct in the DC-ERG than the AC-ERG.