Harmonic Analysis of the Strobe Flicker Electroretinogram in Retinal Disease

The electroretinogram (ERG) elicited by a flickering stimulus has become a useful clinical test for monitoring the progression of retinal disease and for inferring the pathophysiology of the disease process. In the clinical setting, the flicker ERG is usually obtained using a train of strobe flashes. The effect of the disease process is then either derived from an examination of the characteristics of the flicker ERG waveform, such as peak amplitude and implicit time, or from narrow-band filtering of the ERG at the stimulating frequency. However, the interpretation of the flicker ERG can be problematic in cases of retinal disease in which patients have unusual waveform shapes. An example is the double-peaked 30 Hz flicker ERG waveform reported by Miyake et al. (1987) in patients with "incomplete" congenital stationary night blindness (CSNB). We recently identified two patients with typical retinitis pigmentosa (RP) who showed also showed a double-peaked flicker ERG waveform, indicating that this response abnormality may be found in other types of retinal disorders besides incomplete CSNB. The purpose of the present study was to characterize the harmonic components of the flicker ERG in these RP patients in order to better understand the origin of this anomalous flicker response as well as the flicker ERG of normals.