Guidelines for calibration of stimulus and recording parameters used in clinical electrophysiology of vision

In order to perform a technically adequate clinical electrophysiological procedure it is necessary to calibrate the stimulating and recording equipment. Published standards for the electroretinogram (ERG)[1], electro-oculogram (EOG)[2], visual evoked potential (VEP)[3], and guidelines for the Pattern ERG (PERG)[4] specify stimulus and recording parameters. Yet, most commercial instruments do not provide the means for calibration of these parameters. The goal of this document is to provide guidelines for proper calibration of stimulus and recording equipment. The need for such guidelines is clear on both clinical and scientific grounds. Stimulus and amplifier characteristics have substantial effects on the peak latency and amplitude measurements that are commonly used in clinical electrophysiology. Many review articles on clinical electrophysiology emphasize the need for establishing norms for each laboratory as a function of age and gender rather than relying on published norms. However, if stimulus and recording parameters are not calibrated periodically, then these norms may actually be misleading due to changes in stimulus or recording conditions induced by aging of equipment or inadvertent change in settings.