Simulated nystagmus suppresses pattern-reversal but not pattern-onset visual evoked potentials.
OBJECTIVE
The aim of this study is to quantify and compare the effects of simulated horizontal nystagmus on pattern-reversal and pattern-onset visual evoked potentials (VEPs).


METHODS
In eight visually normal subjects with normal oculomotor behaviour, we monitored eye movements and recorded pattern-reversal and pattern-onset VEPs from occipital electrodes. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner at four different amplitudes (0, 1, 2, and 3 degrees ) with a 4 Hz saw-tooth waveform to simulate horizontal jerk-nystagmus.


RESULTS
Retinal image motion nearly abolished the pattern-reversal VEPs (maximal reduction by 85%; mean reduction by 72%, P<0.001), while there was a non-significant reduction (mean reduction by 15%) of the pattern-onset VEPs.


CONCLUSIONS
The differential effect of simulated nystagmus on pattern-reversal and pattern-onset VEPs resembles that reported in studies on nystagmus patients. We conclude that the interaction of retinal image motion with the stimulus is sufficient to explain the reduction of pattern-reversal VEPs in patients with nystagmus and propose simulated nystagmus as a useful tool to test the influence of nystagmus on the efficiency of VEP stimuli.


CONCLUSIONS
This study demonstrates how horizontal jerk-nystagmus can be simulated and suggests possible mechanisms by which nystagmus reduces VEP responses.
Visual Processing Laboratory, Universitäts-Augenklinik, Leipziger Str. 44, 39120 Magdeburg, Germany.
Michael B
MB
Hoffmann
Petra S
PS
Seufert
Michael
M
Bach
D000328:Adult; D004585:Electrooculography; D005074:Evoked Potentials, Visual; D005133:Eye Movements; D006801:Humans; D009759:Nystagmus, Pathologic / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods*; D012160:Retina / Q000503:physiopathology; D015349:Vision, Monocular