par Zanen, André 
Référence Mémoires de l'Académie royale de médecine de Belgique, 7, 9, page (603-680)
Publication Publié, 1972
Référence Mémoires de l'Académie royale de médecine de Belgique, 7, 9, page (603-680)
Publication Publié, 1972
Article révisé par les pairs
| Résumé : | Fast Photovoltages (FPV) preceding the A wave of the electroretinogram were recorded from the cornea of normal human eyes stimulated by intense white flashes. Recording the FPV's from the eye requires powerful brief flashes of light (about 1000 times more intense than the flashes classically used in electroretinography). Special steps must be taken to avoid the contamination of the FPV's by photic and electric artifacts. The Early Receptor Potential (ERP) is the FPV due to action of light on visual pigments. In the dark adapted human eye, the ERP consists of a R1 wave, recorded positive at the cornea and has no measurable latency, followed by a R2 wave, negative at the cornea, which is slower and larger. The ERP is suppressed when the flash is delivered immediately after a thorough bleaching of the eye. Its amplitude then increases exponentially during dark adaptation and reaches its dark adapted value with a half time of 135 sec. The amplitude of the early potential is studied versus intensity of the flash for a range covering 4 log. units. It increases linearly from 0.3 μV (measured by averaging) to 120 μV. For higher values its amplitude progressively levels off. On repetitive stimulation, its amplitude is progressively reduced, because each flash of the sequence bleaches a constant fraction of the visual pigment present in the eye. From the decrement between the response to the first and to the second flash, the destruction of 10% of the visual pigment of a dark adapted eye is estimated to produce an ERP of 70 μV. Besides, for the high intensity range, the ERP is contaminated by an early potential, negative at the cornea, which is generated by photostable pigments. This last potential may still be considered as negligible for amplitudes of the FPV under 100 μV. Its relative contribution to the FPV becomes more important for brighter flashes, because the ERP component saturates and the photostable component does not. Early potentials from the visual and from the photostable pigments are also recorded from fresh cadaver eyes. The photostable potential can be obtained from the isolated pigmentary epithelium choroid complex and may be attributed to the action of light on melanin. |
