Purchase this article with an account.
J. P. Kelly, J. O. Phillips, A. H. Weiss; Effect of Actual Nystagmus Waveforms on Check Reversal and Pattern-Onset VEPs. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2339.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The checkerboard reversal VEP is known to be selectively reduced under conditions of simulated nystagmus using predictable triangle or sawtooth waveforms.1,2 This study recorded check reversal (CR) and pattern-onset (PO) VEPs during retinal image motion that replicates actual positional error and variable velocity profile from a patient with motor nystagmus.
Four visually normal adults and one 7-year-old child control had VEPs recorded to standard check reversal (60’, 2.7 rev/sec) and pattern onset/offset VEPs (vertical sinewave gratings, 1 cy/deg 150/ 500 msec and 60’ check patterns 50/ 500 msec) under equiluminant conditions. Subject eye movements were simultaneously recorded using EOG to reject EEG epochs without stable fixation before averaging. Nystagmus waveforms were created from 60 Hz video-oculography recordings in the patient in which 18% percent of the recording contained epochs (16-70 msec) of slow velocity < 2 deg/sec with peak slow phase velocities of > 60 deg/sec.
For CR, simulated nystagmus reduced VEP amplitude to noise levels (92% +/- 7%; p < 0.05). For grating PO, simulated nystagmus elicited insignificant changes in amplitude (range 55% to 250%; mean 107%; p > 0.6). Two subjects showed a decrease in latency and improvement in waveform with simulated nystagmus. The child subject’s amplitudes were >4 times larger than adults. For check PO, simulated nystagmus did not elicit a change the VEP waveform or amplitude (mean change 96% +/- 19%; p = 0.9).
CR VEP amplitude is reduced to noise levels despite epochs of velocity < 2 deg/sec. We propose the results occur due to the requirement of VEP averaging across the whole stimulus presentation, and that position uncertainty in addition to retinal image motion contributes to the reduced CR VEP in patients with nystagmus. Therefore, CR VEP mechanisms require consistent registration of contrast reversing contours. Our results are similar to those reported for predictable sawtooth waveforms1 but the underlying mechanism may differ.1 Hoffmann et al., Clin Neurophysiol 2004;115:2659.2 Arlt & Zangemeister, Neuro-Ophthal 1990;10:241.
This PDF is available to Subscribers Only