Influence of blur on the visual evoked magnetic response to a pattern reversal stimulus

A. Slaven, Richard A. Armstrong

Research output: Unpublished contribution to conferencePosterpeer-review


Blurring a pattern reversal stimulus increases the latency and decreases the amplitude of the visual evoked potential (VEP) P100 peak. Recording the visual evoked magnetic response (VEMR) is some subjects may therefore be difficult because their spectacles create excessive magnetic noise. Hence, the effect of varying degrees of blur (-5 to +5 D) on the VEMR was investigated in three subjects with 6/6 vision to determine whether refraction with non-magnetic frames and lenses was necessary before magnetic recording. Small (32') and larger (70') checks were studied since there is evidence that blurring small checks has a more significant effect on the VEP compared with large checks. The VEMR was recorded using a single channel dc-SQUID, second order gradiometer in an unshielded laboratory. The latency (ms) and amplitude (fT) of the most prominant positive peak within the first 130 ms (P100M) were measured. Blurring the 32' checks significantly increased latency aand reduced the amplitude of the P100M peak. The resulting response curves were parabolic with minimum latency and maximum amplitude recorded at 0 D. Blurring the 70' check had no significant effect on latency or amplitude. Hence, the magnetic P100M responds similarly to the electrical P100 in response to blur. It would be essential when recording the VEMR that vision is corrected with non-magnetic spectacles especially when small checks are used.
Original languageEnglish
Publication statusIn preparation - 1993
EventMeeting of the Society for Experimental Optometry - Birmingham (UK)
Duration: 26 Jul 199327 Jul 1993


ConferenceMeeting of the Society for Experimental Optometry
CityBirmingham (UK)

Bibliographical note

Papers presented at the meeting of The Society for Experimental Optometry, in Birmingham (UK) on 26 – 27 July 1993, Ophthal Physiol Opt 14:P108, 0275-5408.


  • blurring a pattern reversal stimulus
  • visual evoked potential
  • P100
  • visual evoked magnetic response
  • refraction
  • magnetic recording


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