Effect of reference point on visual evoked potentials: clinical relevance.

For clinical purposes the VEP is generally recorded from the mid-occipital region referenced to the vertex or mid-frontal region. This may lead to interpretive errors that can be avoided if a relatively inactive reference point, such as linked mastoids, is used simultaneously. The additional recording derivation may also be helpful in clarifying aberrant or ambiguous wave forms. The diagnostic yield from the two montages is similar, although the linked-mastoid reference provides a greater number of technically inadequate recordings due to smaller size of P100 and increased contamination by muscle artifact.