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Multifocal topographic visual evoked potential: improving objective detection of local visual field defects
A I Klistorner1, S L Graham, J R Grigg
1Department of Ophthalmology, Save Sight Institute, Sydney University, Australia.
Investigative Ophthalmology & Visual Science
|May 14, 1998
Summary
Bipolar occipital electrode placement improves multifocal visual evoked potential (VEP) testing for detecting local visual field defects. This method offers superior signal detection compared to monopolar recording, aiding in objective diagnosis.
Area of Science:
- Neuroscience
- Ophthalmology
- Visual Electrophysiology
Background:
- Visual evoked potential (VEP) is a key electrophysiological test for assessing visual pathway function.
- Objective detection of local visual field defects remains a challenge in clinical practice.
Purpose of the Study:
- To evaluate the relationship between visual field stimulation, electrode placement, and cortical responses.
- To enhance objective detection of localized visual field impairments using multifocal VEP.
Main Methods:
- Multifocal VEP was recorded using pseudorandomly alternated pattern stimuli in 12 normal subjects and 7 patients with visual field defects.
- Both monopolar and bipolar electrode placements over the occipital cortex were utilized.
- Visual field assessment extended up to 26 degrees of eccentricity.
Main Results:
- Bipolar electrode placement over the active occipital cortex yielded robust signals across the tested visual field.
- While amplitudes were similar, opposite polarities in upper and lower hemifields caused VEP cancellation with full-field analysis.
- Bipolar VEP results correlated well with Humphrey visual field defects, showing signal loss in scotoma areas.
Conclusions:
- Multifocal VEP with bipolar occipital electrodes provides superior topographical correspondence with visual field defects compared to monopolar recordings.
- Separate analysis of upper and lower hemifields is recommended to mitigate cancellation effects and optimize assessment.
- This technique represents a significant advancement for the objective diagnosis of local visual field defects.