Electroretinographic study of the rod-cone break in the dark adaptation curve in man.

Many studies on humans have been published comparing psychophysic and electroretinographic (ERG) adaption to dark. In both cases, there is evidence of a break commonly called "alpha point"; such a break occurs when the subject has first been exposed to an adequate previous bleaching. Jayle has summarized this problem extremely well.1-2 In these publications dealing with the electroretinographic response, it is generally the B-wave amplitude or occasionally the A-wave which serve as response criteria. As a rule, high-intensity stimuli, such as those produced by xenon flash tubes, are used in clinical electroretinography. Under such experimental conditions, four main components have been defined, two of which are negative, A-l and A-2 and two are positive, B-l and B-2. The first waves in each of these groups have often been paired to form two systems: the first, the Al B-l system, expressing cone or photopic activity, the second, the A2 B-2 system, expressing rod or scotopic activity. These two systems would operate at different time latencies, that of the rods being longer than that of the cones.