L'électro-rétinogramme de l'homme

Abstract

A method of perimetric electroretinography is described, by means of which the action of duration, intensity, colour and location of the light stimuli on the human ERG can be studied. The analysis of more than 1,800 records confirms that the human ERG belongs to Granit's E type. Its most characteristic feature is the b potential, quantitatively defined by the latency, the duration of the ascendant phase or culmination time, and the amplitude, a and c potentials are small and often variable. There is no positive off-effect. Binocular electroretinography elicits, together with a normal ERG in the illuminated eye, a consensual response in the other eye, a reaction which seems to be coincident with the pupillary consensual reflex. The ability of the retina to differentiate light changes can be measured objectively by the fusion frequency of the small b potentials, elicited by flicker stimulation. The fusion occurs normally at a rate of more than 19–20, often of more than 26 flashes per sec. The ERG in man varies not only with the duration, but also with the intensity of the stimulus. Increase of intensity produces a decrease in the latency and culmination time of potential b, as well as an increase in its amplitude. Perimetric electroretinography permits the study of the reactivity of various retinal areas and the objective delimination of the visual field. In the normal subject, stimulation of peripheral areas (60° nasal retina) produces an ERG with longer latency and culmination time, and smaller amplitude of the b potential than those elicited by stimulation of more central areas. Stimulation of the retina with monochromatic light stimuli elicits: 1. A photopic component, particularly marked when the central area of the retina, adapted to light, is stimulated with red light, 2. A scotopic component, with slow and broad ‘b’ potential, particularly marked when the peripheral area of the retina, adapted to darkness, is stimulated with blue light. This scotopic response shows a longer culmination time when the wave-length of the stimulus decreases: it reaches its maximum when the peripheral retina is stimulated with blue light. Simultaneous recording of ERG and EEG permits measurement of the retino-cortical time, as well as of the alpha-blocking time. The retino-cortical time, that is, the latency of the evoked potentials, is more constant than the alpha-blocking time, being only 50 msec. (±15). Measurement of the retinal time, the retino-cortical time, and the alpha-blocking time can provide useful information about the functional state of the various sections of the visual tracts and centres.