Nystagmus and visual evoked potentials

Abstract

The pattern reversal evoked potentials test (PR-VEP) is widely used for assessing the integrity of the anterior visual pathways. With the conventional black and white check stimulus, a successful test requires that the patient be able to fixate at the center of the screen. Although in most patients with nystagmus a reliable VEP can be obtained, we have noted that some patients may have no response even in the absence of anterior visual pathway dysfunction. We suspected that this was due to a decrease in foveation of each check, secondary to the nystagmus. To test this hypothesis we evaluated 4 patients with marked horizontal nystagmus and found no evidence of anterior visual pathway dysfunction. The conventional PR-VEP showed absence of P100 response bilaterally in all patients. With horizontal grating stimulus, two patients demonstrated well defined P100 responses bilaterally and in the other two, a unilateral response was noted. The latency and amplitude of all of these responses was normal. A study of six normal individuals (controls) with both checkerboard stimulus and horizontal grating revealed P100 responses with normal, comparable latencies. This data demonstrates the clinical usefulness of the horizontal grating technique in patients with marked nystagmus, in whom the conventional VEP has failed to register P100 component of the visual evoked test.

Key Words:

• nystagmus
• visual evoked potentials