ERG dark adaptation in the unanesthetized rabbit.

The amplitude of the rabbit scotopic electroretinogram (ERG) is notoriously labile both in day-to-day variations in the same animal1 as well as in the wide range seen in normal controls. This seriously impairs the rabbit's usefulness as a model in long-term experiments. Part of the reason for this difficulty appears to lie in the traditional methods of obtaining and assessing adaptation preparatory to performing the ERG—specifically, in the amount of light pre-adaptation and the subsequent length of dark adaptation which the animal undergoes. Full dark adaptation is thought to have been reached when b-wave amplitude fails to increase materially with further time in the dark. It is the lack of firm knowledge regarding the length of time necessary for dark adaptation in the rabbit that prompted this investigation. The degree of exposure to light prior to dark adaptation has been shown to have a significant effect on the length of time necessary to reach full dark adaptation.2'3 Elenius3 measured the ERG amplitude in anesthetized rabbits after four hours in the dark without light pre-adaptation, (8000 Lux for 30, 10, three, and one minutes), and followed the subsequent increase in ERG amplitude until the value of 100%, total dark adaptation for that animal, was reached. He found that at one minute and three minutes of light pre-adaptation the animal took 90 to 100 minutes to return to the 100% level. With 30 minutes of light pre-adaptation this