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Alexander I. Klistorner, Stuart L. Graham; Electroencephalogram-Based Scaling of Multifocal Visual Evoked Potentials: Effect on Intersubject Amplitude Variability. Invest. Ophthalmol. Vis. Sci. 2001;42(9):2145-2152.
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© 2015 Association for Research in Vision and Ophthalmology.
purpose. The interindividual variability of the visual evoked potential (VEP)
has been recognized as a problem for interpretation of clinical
results. This study examines whether VEP variability can be reduced by
scaling responses according to underlying electroencephalogram (EEG)
methods. A multifocal objective perimeter provided different random
check patterns to each of 58 points extending out to 32° nasally. A
multichannel VEP was recorded (bipolar occipital cross electrodes, 7
min/eye). One hundred normal subjects (age 58.9 ± 10.7 years)
were tested. The amplitude and inter-eye asymmetry coefficient for each
point of the field was calculated. VEP signals were then normalized
according to underlying EEG activity recorded using Fourier transform
to quantify EEG levels. High α-rhythm and electrocardiogram
contamination were removed before scaling.
results. High intersubject variability was present in the multifocal VEP, with
amplitude in women on average 33% larger than in men. The variability
for all left eyes was 42.2% ± 3.9%, for right eyes 41.7% ± 4.4%
(coefficient of variability [CV]). There was a strong correlation
between EEG activity and the amplitude of the VEP (left eye, r = 0.83; P < 0.001; right
eye, r = 0.82; P < 0.001).
When this was used to normalize VEP results, the CVs dropped to 24.6%±
3.1% (P < 0.0001) and 24.0% ± 3.2%
(P < 0.0001), respectively. The gender difference
was effectively removed.
conclusions. Using underlying EEG amplitudes to normalize an individual’s VEP
substantially reduces intersubject variability, including differences
between men and women. This renders the use of a normal database more
reliable when applying the multifocal VEP in the clinical detection of
visual field changes.
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