The retina adapts to average light intensity but also to the range of light intensities (contrast). A study by Baccus and Meister, in this issue of Neuron, identifies three ways that ganglion cells and interneurons adapt to high contrast: shorten integration time, reduce gain, and depolarize. Only the depolarization decays, over tens of seconds.
Demb, J. B. (2002, December 5). Multiple mechanisms for contrast adaptation in the retina. Neuron. Cell Press. https://doi.org/10.1016/S0896-6273(02)01100-5