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Abstract #6393 Published in IGR 3-2
Electroencephalogram-based scaling of multifocal visual evoked potentials: effect on intersubject amplitude variability
Klistorner AI; Graham SLInvestigative Ophthalmology and Visual Science 2001; 42: 2145-2152
PURPOSE: The interindividual variability of the visual evoked potential (VEP) has been recognized as a problem for the interpretation of clinical results. This study examines whether VEP variability can be reduced by scaling responses according to underlying electroencephalogram (EEG) activity. METHODS: A multifocal objective perimeter provided different random check patterns to each of 58 points extending to 32° nasally. A multichannel VEP was recorded (bipolar occipital cross electrodes, 7 min/eye). One hundred normal subjects (aged 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 females on average 33% larger than in males. 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. ; 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 males and females. This renders the use of a normal database more reliable when applying the multifocal VEP in the clinical detection of visual field changes.
Dr A.I. Klistorner, Save Sight Institute, Department of Ophthalmology, Sydney University, Sydney, Australia
Classification:
6.7 Electro-ophthalmodiagnosis (Part of: 6 Clinical examination methods)