Faculty Bibliography

The P300 cortical evoked potential was compared to the P100 wave of the visual evoked potential by means of appearance/disappearance gratings. The spatial frequency of the novel stimulus was varied to compare the effect of task sensory difficulty on both P100 and P300 potentials. The P100 showed a steady increase in latency with the spatial frequency of the uncommon stimulus, and a degree of amplitude tuning consistent with the contrast sensitivity function. The P300 showed marked changes in both amplitude and latency dependent almost wholly on the proximity of the uncommon stimulus spatial frequency to that of the common stimulus. Motor reaction time showed elements of both the P100 and P300 response patterns. The results are consistent with a model in which, after visual information arrives at the visual cortex, processing is parallel and interdependent. In this model, the amplitude and latency of the P100 cortical evoked potential are governed solely by properties intrinsic to the stimulus, whereas the amplitude and latency of the P300 are functions of the degree of stimulus mismatch

The focal electroretinogram (FERG) was used to examine temporal frequency tuning at the outer retinal level in humans by measuring temporal modulation thresholds. Changes in FERG thresholds as a function of ambient light level were compared to temporal modulation thresholds obtained psychophysically using the same stimuli. At lower temporal frequencies, both FERG and psychophysical thresholds changed sensitivity proportional to the mean illuminance level. At higher illuminance levels, both threshold measures were relatively independent of illuminance. The comparison of the FERG to the behavioral data suggest that most of the adaptation-dependent changes in temporal sensitivity in humans occur at the level of the photoreceptor complex

Previous studies of early diabetic retinopathy have shown that oscillatory potential (OP) amplitudes are reduced in many diabetic patients. OP amplitude is believed to be a more sensitive indicator of the development of future retinopathy than b-wave amplitude of the scotopic electroretinogram (ERG). Because OPs measured to a bright white flash reflect both rod and cone system activity, it is important to compare OP amplitudes to photopic ERG measures as well as scotopic measures in early diabetic retinopathy. In this study, OPs and ERG responses were measured under photopic and scotopic conditions in a group of diabetic patients. Although OPs were reduced in amplitude in the diabetic group, several other parameters of the scotopic and photopic b-waves were impaired. The results indicate that b-wave activity may indicate retinal changes in early diabetic retinopathy in the same manner as the OPs

Seven patients with longstanding monocular optic atrophy had normal flash electroretinograms when compared to the results from control observers or when compared to the results from their own unaffected eye, or the eyes of control observers. These findings are contrasted with prior investigations that report either depression or augmentation of ERG amplitudes. We found that optic nerve damage does not cause trans-synaptic changes in the retina, or loss of efferent inhibition that can be measured by electroretinography

Eight patients with malignant gliomas were monitored with clinical examinations to study the effects of the combination of intravenous administration of carmustine and infraophthalmic intra-arterial administration of cisplatin on retinal and optic nerve function. Three patients developed a severe macular retinal pigment abnormality in the eye ipsilateral to the intra-arterial infusion. Electrophysiologic studies disclosed no evidence of a generalized disturbance in the photoreceptors, middle retinal layers, or retinal pigment epithelium. In contrast to previous studies involving patients whose visual loss was caused by vaso-occlusive lesions in the retina and optic nerve, our study involved patients with clinically significant maculopathy, that was not vascular in origin and that developed after treatment with carmustine and cisplatin. We suggest that the deficit may result from a localized retinal pigment disturbance in the macula