Functional examinations of visual channels: Physiological basis

Abstract

In this paper, technical details of visual evoked potentials (VEP) assessment and pattern electroretinography (PERG) are reviewed. Both methods are used to perform an objective functional examination of visual channels and to clarify the level, at which they have been damaged. Contributions of parvo-(P), magno-(M) and koniocellular (K) systems to the morphology of PERG and VEP responses are discussed with account to test conditions, selectively supportive of the activity of particular cell populations. The review analyzes the physiological role of such stimulation parameters as brightness and color contrast of the pattern elements as well as spatial and temporal frequency in detecting dysfunction of color channels and mistuning of the P- and M-pathways. Different times taken for neuronal integration and signal conduction along the M- and P-pathways determine the timing of the P- and M-VEP components, allowing us to judge their contribution to VEP morphology from the same recording.