Multi-channel pattern VEPs with full and half field stimulation: methods of interpretation and diagnostic evaluation

To describe methods of evaluating multichannel full and half field pattern VEPs using the ISCEV VEP Standard montage.

The dependence of full field and half field pattern VEPs on retinal areas and cortical generators is reviewed and applied to the interpretation and evaluation of multichannel half field pattern VEPs.

There are predictable differences in the trans-occipital distributions of components of monocular full, and half field, pattern-reversal and full field, onset-offset VEPs. In combination, the differing distribution and dependence of these components on foveal and macular fields can help to identify and localise chiasmal and retro-chiasmal dysfunction and distinguish this from trans-occipital distribution due to individual variations of cortical architecture. A decision tree synthesising published evidence and current practice is suggested to guide interpretation of trans-occipital VEP distributions.

The routine application of two additional lateral channels to acquire multichannel VEPs is quick, easy and adds clinical diagnostic value. The combination of full and half field pattern-reversal and fullfield, onset-offset VEPs can help evaluate chiasmal and retro-chiasmal visual pathway function, and minimise false positive interpretation of asymmetric VEP distributions, which may be due to cortical architecture or cranial anatomy alone.