Optimizing Electrode Positions and Analysis Strategies for Multifocal VEP Recordings
Meigen T., Krämer M.
Dept. of Ophthalmology, Wuerzburg University
Purpose: The multifocal VEP (mfVEP) can be used for functional testing of the optic nerve. In this study we quantified the benefits of using a multi-channel recordings instead of single-channel recordings.
Method: We used a dartboard pattern with 60 fields and a diameter of 41° to record 2 monocular and one binocluar mfVEP in 30 normal subjects. 4 electrodes were placed 4 cm to the left, right, top, or bottom of the inion. By recording or by linear combination of the recorded mfVEPs we obtained the VEPs of the 4 positions when referenced to FPz as well as the VEPs between the 4 occipital positions. For each VEP trace a "signal" amplitude between 45ms and 150ms, and a "noise" amplitude between 325ms and 430ms was derived with a rms method. For each subject and each recording condition the area under a corresponding ROC curve was used to quantify the ability to discriminate between signal and noise.
Results: (1) The electrode position 4cm above the inion was involved in those 4 recording conditions that showed the highest sensitivity. (2) The 3 least sensitive conditions were VEPs recordings with the reference electrode at FPz. (3) By combining the 3 most sensitive conditions the area under the ROC curve could be increased significantly (ANOVA, p<0.0001). (4) The best combination was to choose the largest rms amplitude from all 3 channels which was more effective than simply averaging the 3 channels. (p=0.001
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