Conventional clinical electrophysiology provides us with a range of tools to assess the visual pathway. The basic clinical test procedures are now well established, and the International Society for Clinical Electrophysiology of Vision (ISCEV) produces standards to ensure the quality control of acquisition and interpretation of the various clinical procedures. Although these base procedures are well established, they continue to contribute new information to our understanding of human visual processing and the effects of a wide range of clinical conditions on visual function.

In the last decade, multifocal electrophysiology has been a significant addition to the range of electrodiagnostic procedures. The technique adds a spatial dimension to electrophysiology and provides a new tool to investigate the nonlinear processing mechanisms of human vision. The basic details of multifocal stimulation can be found in Sutter's original papers.^57,61

A thorough understanding of multifocal electrophysiology requires an extensive knowledge of mathematics and the engineering principles of signal detection theory. However, this detailed knowledge is not necessary for the clinical electrophysiologist who wants to use the technique for vision research or clinical investigation. The purpose of this chapter is to illustrate, for those who are familiar with conventional electrophysiology, the differences that the multifocal technique brings and provide pointers to those who may wish to explore the mathematical or engineering background in more detail. The chapter aims to give an overview of the elements of a multifocal system, describe the signal waveforms and their interpretation, explore clinical applications, and provide indications for future multifocal research.