May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
Effect of fixation tasks on the multifocal VEPs
Author Affiliations & Notes
  • A. Martins
    Ophthalmology/Eye Health, Sydney Eye Hosp–Univ Sydney, Sydney, Australia
  • Footnotes
    Commercial Relationships  A. Martins, None.
  • Footnotes
    Support  none
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 5489. doi:
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      A. Martins; Effect of fixation tasks on the multifocal VEPs . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5489.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Aim: In this study we investigated the effects of 3 different foveal fixation conditions on the multi–focal visual evoked potential (mVEP). A more complex visual fixation task has been known to suppress peripheral signals in subjective testing. Method: Twenty normal subjects had monocular multifocal VEPs recorded using the ObjectivisionTM objective perimeter. This allowed simultaneous stimulation of 56 segments of the visual field to an eccentricity of 26 degrees. The mVEP was recorded using three different fixation conditions in random order. During Task 1 the subject passively viewed the fixation point consisting of a central black dot. For Task 2 alternating numbers were displayed within the fixation point; the subject was required to press a button when the number ’3’ appeared. Throughout Task 3 the subject was required to summate these numbers. Results: Amplitude verses eccentricity graphs of the three tasks illustrated similar curves, rising to a peak in the mid field at Ring 3. Further analysis revealed the second task, which included a motor component, resulted in a significant reduction of amplitudes in the periphery of the visual field (Mann Whitney p<0.01); the central areas remained unchanged. Higher mental activity was required for the third task. This produced significantly enlarged amplitudes in the central visual field, in comparison to the attention (p=0.005) and fixation tasks (p=0.003), and resulted in minimal change in the periphery. Latencies demonstrated no significant difference between each task nor at any eccentricity (p>0.05). Conclusion:We concluded the use of an interactive motor task appeared to reduce amplitudes in the periphery by approximately 7%. This task involved a higher order of visual and motor activity. However, in addition to this, the role of increased motor noise from muscle tension needs to be considered. Task 1 was found to be the most difficult to perform because of loss of interest. It was noted to be associated with a high level of alpha rhythm. The mathematical fixation task required higher cognitive activity. A possible explanation is that higher cortical processing influences foveal amplitudes.

Keywords: electrophysiology: clinical • visual fields • perimetry 
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