Figure 2. PER 2::LUC bioluminescence rhythms in RPE-choroid and retina. A: Representative example of PER2::LUC rhythms in RPE-choroid. B: The circadian rhythms of RPE-choroid persisted more than 50 days. C: Representative example of PER2::LUC rhythm in retina. D: The circadian rhythms of retina persisted more than 70 days. Although the circadian rhythm in the bioluminescence damped out after 6–7 days, a medium exchange could reinitiate the circadian rhythm in these cultures. The arrows indicate the days on which the medium in the culture was replaced.