To investigate the cortical mechanisms for motion perception in human V5, we measured visual evoked magnetic fields in response to random dot kinematograms (RDKs) of three different coherence levels (50, 70 and 100%) using a 122-channel whole-head magnetometer. As the coherence level increased, the peak amplitude measured by the root mean square (RMS) of the local response increased significantly (7.4+/-1.0, 9.5+/-1.5 and 15.5+/-3.2 fT/cm on the right, 6.4+/-0.3, 7.8+/-0.7 and 12.5+/-0.9 fT/cm on the left; for the coherence level of 50, 70 and 100%, respectively). There was no significant difference between the hemispheres. As for the peak latency, there was no significant difference in terms of coherence levels or hemispheres. The response was localized posterior to the junction of the ascending limb of the inferior temporal and lateral occipital sulci (human V5). These findings indicate that processing of global motion in terms of the synchronized portion correlates well with the response amplitude but not with its latency. Thus, we could estimate the magnetic responses of human V5 non-invasively by presenting different coherence levels of the visual motion stimuli. Hemispheric laterality was recognized, although the dominant side varied among subjects.
We compared the best-corrected Snellen acuity (SA) and the pattern reversal visual-evoked response (PVER) acuity in normal subjects and patients. Forty-two eyes of 42 normal subjects were controls; 457 eyes of 329 patients comprised the patient group. A steady-state stimulus with five check sizes ranging from 160 to 10 min in 1.0-octave steps was used. The PVER acuity was derived from the best-fit linear function relating the amplitude to the log-adjusted check size. Three intercepts of 0, 1 and 2 μV were used in both groups, and the PVER acuities were called P°, P1 and P2. The SAs in normal subjects ranged from 20/15 to 20/20 (mean, 20/18.3) and in patients from 20/15 to 20/1,600 (mean, 20/56.9). In normals, the P° showed the best agreement with the SA (mean acuity difference, +0.34 octave). The SA and P° agreed within ± 2.0 octaves in 33/42 (78.6%) eyes. In patients, the P° also showed the best agreement with the SA; 306/457 (67.0%) eyes showed an acuity difference within ± 2.0 octaves. Unlike normals, 83/ 457 (18.2%) eyes showed an acuity difference > -3.0 octaves. These eyes mostly had optic nerve disease with a flattened PVER amplitude-check size function curve. The P° seems to correlate better with SA than P1 and P2, but this analytical method may be less effective in the presence of certain pathologic conditions.
Paraneoplastic retinopathy is a cancer-related non-metastatic retinopathy mainly associated with lung cancer. We examined two patients with presumed paraneoplastic retinopathy, both ophthalmologically and electrophysiologically. Both patients presented with initial visual complaints of moderate reduction of visual acuity. No specific fundus anomaly was found in the fundus except for a mild attenuation of the retinal arteries. The electroretinogram and pattern reversal visual evoked responses were either markedly reduced in amplitude or non-recordable. The electrooculogram recorded in one patient demonstrated a markedly reduced light peak/dark trough ratio. These results indicate the presence of a severe and diffuse bilateral retinal dysfunction, despite the relatively good visual acuities and mild fundus changes. Electrophysiological evaluations play an important role in the diagnosis of paraneoplastic retinopathy.
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