Visual-Evoked Potential

or VEP; A method for assessing the objective response to visual stimulus, by non-invasively measuring the voltage potential around the eye. This is intended to measure changes in the signal on the Phototransduction Pathway. The method is similar to Electroretinography. When the visual stimulus is changed and this change is strong enough to be “noticed” by the Phototransduction Pathway, then there will be a wave in the potential’s time trace (waveform). For example, a Protan would not show a change in potential for an image flashing between isoluminant purple and blue, but this wave would be present in a color normal individual.

Other ‘classical’ colorblindness tests, such as the Ishihara Test) are subjective, in that they require interpretation and a response by the subject. If the subject is too young to interpret the image, or the subject is non-cooperative, then a subjective test is useless. The VEP is an objective measure of visual stimulus, so is applicable to young and non-cooperative subjects.