ERG of humans without C-wave

Vincristine-induced changes in the retina of the isolated arterially-perfused cat eye

We have attempted to determine in this study whether the arterial administration of vincristine produces in cat the functional defects associated with hereditary and vincristine-induced night blindness in man. Using the isolated perfused cat eye, it has been possible to mimic some of the essential features of human night blindness, namely, retention of normal rhodopsin chemistry and normal photoreceptor activity, with marked suppression of the ERG b-wave. In addition, we find that vincristine produces an early, rapid fall in the c-wave, a potential that arises largely in the pigment epithelium. Ultrastructurally, it appears that many classes of retinal neuron are affected by the drug, but the principal changes in cytoarchitecture are seen in the photoreceptors. Except for the outer segments, paracrystalline deposits were found in all parts of the visual cell. The disruption of the normal microtubular organization of these cells suggests that the drug interferes with the functional integrity of the transport system by which synaptic activity is maintained. By reducing the efficacy of communication between visual cells and their second-order neurons, the electrical responses of post-synaptic elements is degraded. The route by which vinca alkaloids reach the neural retina is still uncertain, but our preliminary studies using HRP indicate that the relatively high concentration of vincristine used in this study may be responsible for compromising the blood-retinal barrier.

Effects of hypoxia and hyperoxia on the human standing potential

We report that the human standing potential, measured by the EOG, rises slowly when oxygen saturation is lowered to near 80% by breathing a controlled oxygen-nitrogen mixture. The standing potential falls abruptly by 20-30% of its amplitude when the oxygen saturation returns to 100%. These changes can be generated reproducibly, with minimal discomfort, under conditions that could be adopted for clinical use. Animal experimental studies by Linsenmeier and Steinberg suggest that this hypoxia-hyperoxia response may be a delayed response to potassium concentration changes in the subretinal space. Since there is no requirement for light and no involvement of the Müller cells, the hypoxia-hyperoxia response may be more specific for pigment epithelial pathology than the c-wave.

The c-wave of the electroretinogram in vitelliruptive macular degeneration (älvdalssjukan)

The d.c. ERG and the EOG were recorded from 6 patients with vitelliruptive macular degeneration (VMD, Alvdalssjukan). All EOGs were highly pathological. The a- and b-waves of the ERG were normal. These are pathognomonic findings in VMD, which starts as a generalized disturbance of the pigment epithelium. No signs of a c-wave were seen in 4 patients. Small c-waves occurred in 2 patients, but only under certain stimulus conditions. The major positive component of the c-wave is produced by the pigment epithelium -- receptor complex. Absent or pathological c-waves in VMD, a pigment epithelial disease, are in good agreement with what is known about the origin of the c-wave.

Examination of the fast oscillation of the corneoretinal potential under clinical conditions

The "fast oscillation" of the corneoretinal potential can be precisely examined by means of cyclic light stimuli and an automatic measuring device. This new procedure is carried out during the period of adaptation as part of the usual EOG-test. Normal values and some clinical findings are presented. The fast oscillation may provide additional information when compared with EOG and ERG results.

The ERG c-wave in vitelliruptive macular degeneration (VMD)

D.c. ERG registrations and EOG recordings were obtained from six patients with vitelliruptive macular degeneration (VMD). In all cases the EOG was highly pathological, but the alpha- and beta-waves of the ERG were normal. This is typical of VMD, which starts as a generalized defect of the pigment epithelium. Four patients showed no evidence of a c-wave. The other patients demonstrated small c-waves, but only under certain stimulus conditions. Thus, varying stimulus durations, intensities and frequencies are sometimes needed to decide whether or not ERG c-waves can be elicited in different diseases or suspected disorders. The findings are in agreement with the presence of a generalized pigment epithelial defect in VMD, since the major positive component of the c-wave is generated by the pigment epithelium-receptor complex.

New approaches to ophthalmic electrodiagnosis by retinal oscillatory potential, drug-induced responses from retinal pigment epithelium and cone potential

New clinical methods are proposed to assess (1) neuronal activities of the retinal inner layers including amacrine cells by means of the oscillatory potential, (2) photopic function through the rapid decay in the off-response and (3) activities of the retinal pigment epithelium through susceptibility of the standing potential of the eye to osmotic stress and to Diamox. These new methods are able to reveal otherwise undetectable retinal disorders.