Wener Passarinho Cella, Adalmir Morterá Dantas, Alexandre Vasconcelos Lima,

INTRODUCTION T he neurological electrical activity set off by a light stimulus is known as visual evoked potential (VEP) and is obtained by skin electrodes placed over the occipital cortex after repeated retinal stimulation. The VEP reflects the optic pathways functionality from the retina until the occipital visual cortex, and the measurable electric wavelets generated by bright flashing lights can be grouped into early components (waves 1, 2 and 3) and late components (waves 4 to 7). The early VEP components are not as constant as the late ones and have a controversial origin, indicating that they might represent the electrical potential of the optic nerve, lateral geniculate body, or even visual striate cortex. There is also evidence that some potentials as early as 30 milliseconds (ms), known as subcorticals, may have a post-chiasmatic origin, bearing no relation to the ones originated from the retina. Electrophysiological evaluation can also be made with the electroretinogram (ERG) but sometimes, the topographical definition of certain lesions can be inconclusive, especially in cases that involve the optic nerve. The possibility to record the electrical potential of the optic nerve was conceived by Sabadel et al., in 1983, using the axonal electrovisiogram (AxEvg) technique. According to these authors, the AxEvg reveals different amplitudes and latencies when compared to those found in the retina and detected in the ERG. In addition, although the AxEvg wavelets represent visual evoked potentials with similar latencies to the early VEP components, the ones obtained in AxEvg have a pre-chiasmatic origin. RESUMO