PubMed1998
Psychogenic disturbance of vision includes various abnormalities such as low vision, abnormal visual field, abnormal color sense and disturbance of binocular function, although there are no abnormalities either in the eyeball or optic nerve, and no organic changes in brain computed tomography (CT) or magnetic resonance imaging (MRI). To clarify these abnormalities, it is necessary first to study the mechanism of visual information processing. In this report, the mechanism of visual information processing such as visual acuity, visual field, vision and attention and binocular function was studied by standard electrophysiological methods as well as by new techniques including electroencephalography (EEG) topography, visual evoked response imaging system (VERIS), and magnetoencephalogram (MEG). The following four items and the possibilities for clinical application were studied and discussed. The subjects were normal adults and child volunteers, patients with disturbance of vision of psychogenic origin, and patients with abnormal visual fields caused by organic changes in the visual pathway. 1. Visual acuity (form vision). 1) Visually evoked potemtial (VEP), early receptor potential (ERP), and MEG examination were carried out for normal subjects and patients with psychogenic disturbance of vision. 2) The P 100 of pattern reversal VEP of the patients showed a significantly higher response. 3) In normal subjects, the P 300 was observed widely around the Pz in the ERPs during Landolt's ring stimulation. 4) In normal children, the P 300 was observed slightly temporal to the Pz. 5) In some patients maximum amplitude of P 300 was observed in the occipital or temporal region, but in other patients there was no P 300 response in any derivation. 6) MEG in patients with the conversion type of psychogenic disturbance of vision showed only 2 small dipolar patterns around 117 ms during flash stimulation. It was quite different from that of normal subjects. 2. Visual field. 1) Multifocal VEP using VERIS could detect experimental artificial hemianopia caused by conclusion of the half visual field in normal subjects. 2) Multifocal VEP could detect hemianopia or quadratanopia. 3) In multifocal VEP in normal subject, off-latency time was about 36 ms longer than on-latency time both in the center and at the periphery of the retina. The ratio of on/off response decreased from the center to the periphery. 4) In MEG using flash stimulation, hemianopia could be detected even in patients with fixation difficulties. 5) As the subjective visual field was not always in accord with the objective field, objective visual field evaluation is important. 3. Vision and attention. 1) To confirm the influence of attention on visual information processings in patients with disturbance of vision of psychogenic origin, a hypothetical 'island of attention' was postulated. 2) The 'spiral visual field' and the 'Inazuma-type visual field' could be explained by application of this hypothesis for patients with disturbance of vision. 3) Three kinds of waves in VEF, W 1, W 2, and W 3, were detected by MEG after the stimulation of line motion illusion. There was a tendency for the latency time on the attention side to be shorter than on the non-attention side in waves W 2 and W 3. 4) There was a tendency for the amplitude of the attention side to be higher than that of the non-attention side in wave W 3. 5) Attention may influence vision. 4. Binocular vision. 1) A stimulus target was devised which did not elicit N 75, P 100, or N 140 waves. When this target was used for stereoptic stimulation, a negative wave was elicited with a latency of 170 to 280 ms. 2) When the same stimulus target without parallax was used, this negative wave was elicited but the amplitude was small. 3) When evoked potentials were measured under the same conditions, an electric dipole was elicited from the occipital to the temporal region by the electric current source. (ABSTRACT TRUNCATED)