Simulated nystagmus reduces pattern-reversal more strongly than pattern-onset multifocal visual evoked potentials.
OBJECTIVE
In patients with nystagmus conventional pattern-reversal visual evoked potentials are severely degraded, while sizeable pattern-onset VEPs can often still be obtained. We tested whether this differential effect of retinal image motion on pattern-reversal and pattern-onset responses also applies to multifocal VEPs (mfVEPs).


METHODS
In eight subjects with normal oculomotor behaviour and vision we recorded pattern-reversal and pattern-onset mfVEPs from an occipital electrode pair to 60 locations of a scaled dartboard-pattern, and to 64 locations of a uniform checkerboard-pattern. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner with a 4 Hz sawtooth waveform at an amplitude of 2 degrees to simulate horizontal jerk nystagmus and of 0 degrees for the reference condition.


RESULTS
For the scaled dartboard-stimulus we observed an eccentricity-dependent effect of induced retinal image motion on mfVEP responses: in the central visual field (0-0.5 degrees), pattern-reversal and pattern-onset responses were reduced by 73 and 42%, respectively. In the periphery (10-16 degrees), only pattern-reversal responses were reduced (by 27%), while pattern-onset responses were enhanced by 39%. Pattern-onset responses to the uniform checkerboard stimulus were enhanced by 17%, while pattern-reversal responses were reduced by 27%.


CONCLUSIONS
Pattern-onset mfVEPs are more efficient than pattern-reversal mfVEPs, if retinal image motion is superimposed onto the stimulus. This is in close correspondence to previous reports on conventional VEPs.


CONCLUSIONS
This study demonstrates a differential effect of retinal image motion on pattern-reversal and pattern-onset mfVEPs and thus suggests stimulus conditions to enhance the efficiency of mfVEP recordings in patients with moderate nystagmus.
Hoffmann
Michael B
MB
Visual Processing Lab, Universitäts-Augenklinik, Leipziger Str. 44, 39120 Magdeburg, Germany. michael.hoffman@medizin.uni-magdeburg.de
Seufert
Petra S
PS
D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology; D009039:Motion Perception / Q000502:physiology*; D009760:Nystagmus, Physiologic / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D012160:Retina / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology