Faculty Bibliography

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

Human cortical visual evoked potentials (VEPs) were retrieved in real time (without averaging). The stimuli were sinusoidal gratings whose contrast was temporally modulated about some mean value. Electrophysiologically determined contrast modulation thresholds were measured at standing contrast over the range from 2.5% to 50%, defining an increment threshold function. Increment threshold functions were obtained under two different spatio-temporal stimulus conditions identified as 'sustained' (4 c/deg grating modulated at 1.5 Hz) and 'transient' (1 c/deg grating modulated at 20 Hz). Under each of these conditions, threshold responses were retrieved at both the fundamental and second harmonic of the contrast modulation frequency. Under 'sustained' conditions log increment threshold responses and the fundamental the second harmonic of the modulation frequency were similar to those at the fundamental except for a saturation effect (i.e., above a mean contrast of 25% there was little further reduction in modulation sensitivity). There was no contrast gain control under 'transient' stimulus conditions. In other words, the same absolute amount of contrast change produced threshold responses for all mean levels up to 25%. This was true at both the fundamental and second harmonic of the modulation frequency. Stimulus differences produce striking differences in the electrophysiologically inferred increment threshold function for grating contrast, but fundamental and second harmonic evoked responses reflect processes with similar increment threshold behavior