Walsh & Hoyt: Traumatic Optic Neuropathies: Visual Evoked Potential

The visual evoked potential (VEP) may be of use in the unresponsive patient suspected of having traumatic optic neuropathy. This is especially true in possible bilateral cases where an afferent pupillary deficit may not be evident. An unresponsive patient with midface fractures and other than normal pupillary responses warrants a VEP investigation. Generally, the actual clinical utility of VEP is limited logistically. A VEP may not be available at the bedside, when the information is most critical, and moving the patient to the evoked potential laboratory may not be possible. In addition, the test requires a highly qualified technician who may not be available after hours. The VEP is useful only when it is not recordablein which case the chance of visual recovery is very unlikely. The VEP can frequently be abnormal but recordable in an amaurotic eye immediately following optic nerve trauma with subsequent extinction. It is thought that the false-positive VEP may be due to a limited number of still intact axons that are able to conduct.