A comparison of two multifocal ERG systems

The First Order Kernel responses (FOK) from a group of 15 normal subjects aged 21-36 yrs were recorded under clinical conditions with the multifocal ERG (MERG) systems VERIS and RETiscan using system-specific software and hardware under Various parameter settings. First, the multifocal ERG's of normal subjects were recorded with the standard-parameters of VERIS and RETIscan. Thereafter the VERIS system parameters were set as close as possible to the RETIscan-setup, and the recordings were repeated. The VERIS parameters changed were the luminance- and contrast-settings of the stimulus-monitor and m-sequence-timing. In addition, the effects of different sampling rates were also examined. The consequences of the parameter changes were analyzed by displaying the peak times of the First-Order-Kernel (P1). The parameter-combinations used for recording lead to system-specific results. By varying the luminance/contrast settings and/or the m-sequence-timing the results can be changed. The amplitude of the recorded results can be influenced by the luminance-settings of the stimulus-monitor, and the topography of the P1 peak times is affected by the m-if-frame-combination of the recording stimulus. With their standard parameters, the two systems give different measures of the PI peak times. By adjusting the recording parameters. these differences can be reduced significantly. The main parameter here is the m-sequence-timing, although the sampling rate must also be taken into account with regard to the accuracy of the recording results.