The average visual response in patients with cerebrovascular disease

The average visual response (AVR) was recorded in thirty patients after a cerebrovascular accident and in fourteen control subjects from the same age group. The AVR was obtained with the aid of a 16-channel EEG machine, a Computer of Average Transients and a tape recorder with 13 FM channels. This made it possible to study different periods after the stimuli and to study the potential distribution of the various components. Primary and secondary parts of the response and the rhythmic response were considered separately and the AVR was also considered as a whole. There were large inter-individual differences in both the patients and the controls. Therefore no general criteria of abnormality of the AVR could be established from the control subjects; criteria of abnormality of the degree of asymmetry between the AVR from the affected and unaffected sides were defined. The absence of waves I or II could not be considered pathological. In our series wave III (peak latency approximately 80 msec) was not infrequently surface positive in the occipital region. The presence of such a positive wave III correlated with the age of the subject both in the patient group and in the group of controls. The primary and secondary responses and the AVR as a whole, recorded from the parietooccipital derivation, were more frequently abnormal in patients with severe cerebral pathology than in those with moderate pathology. Such a correlation could not be found for the AVR recorded from the occipital-to-ear derivation. Similar findings were obtained, independent of the degree of cerebral pathology, for the patients with a disturbance of the visual system. An abnormal asymmetry of the amplitude of the secondary response only occurred in patients with disturbance of the visual system. The amplitude of the rhythmic response was correlated with the amplitude of the alpha rhythm; such a correlation could not be demonstrated for the other components of the AVR. A normal AVR was found more often in controls and in patients with a normal EEG than in patients with moderate or severe EEG disturbances. Determination of the potential field of the AVR with the aid of multi-channel recording did not appear to furnish significantly more information for diagnostic purposes than recording from both parieto-occipital areas. The AVR from the parieto-occipital derivation appeared to provide a better picture of the disturbances of cerebral function than did the occipital-to-ear derivation. Les réponse