CX3CL1 and retinal degeneration: In the present study, we obtained the findings that support the hypothesis as follows: (1) Histopathological examination revealed that microglia that phagocytosed apoptotic cells and migrated into the OS layer were the source of autofluorescent spots, (2) From the fundus whitening and autofluorescence intensity, we were able to know the severity of photoreceptor apoptosis and the thinning rate of the ONL, in other words the severity of the ongoing retinal degeneration, and (3) In the retinas of rd10 mice, fractalkine was expressed in apoptotic photoreceptors unlike those of WT.