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Visual evoked potentials and electroretinography in brain-dead patients
C Machado1, R Santiesteban, O García
1Institute of Neurology and Neurosurgery, Department of Clinical Neurophysiology, Havanna, Cuba.
Documenta Ophthalmologica. Advances in Ophthalmology
|January 1, 1993
Summary
Brain-dead patients show retinal electrical activity but no cortical visual response. Noncephalic references reliably distinguish electroretinograms from true visual evoked potentials, confirming absent brain activity.
Area of Science:
- Neurophysiology
- Ophthalmology
Background:
- Distinguishing retinal activity from cortical responses is crucial in assessing brain death.
- Visual evoked potentials (VEPs) and electroretinograms (ERGs) are key electrophysiological tools.
Purpose of the Study:
- To investigate the characteristics of VEPs and ERGs in brain-dead patients.
- To determine the utility of cephalic and noncephalic references in differentiating retinal from cortical activity in brain death.
Main Methods:
- Simultaneous recording of VEPs and ERGs using light-emitting diode stimulation.
- Employing both cephalic and noncephalic references in 30 normal subjects and 30 brain-dead patients.
Main Results:
- In brain-dead patients, ERG a- and b-waves were present with cephalic references, while VEPs showed inverse polarity, similar morphology, and reduced amplitude compared to ERGs.
- With noncephalic references, ERGs remained unchanged, but VEPs showed no response, except for two cases with minimal, attenuated spread from the ERG.
Conclusions:
- A noncephalic reference effectively eliminates contamination, confirming the absence of cortical visual response in brain-dead individuals.
- Electrical activity in brain-dead patients is confined to the retina, with no true cortical visual processing occurring.