ELISA analysis revealed that the levels of soluble fractalkine were increased in the 661W control group and the 661W+MG co-culture group. The difference between them is not statistically significant at 6-hour and 12-hour time points. At other time points, the release of soluble fractalkine in the 661W control group was less than that of the co-culture group due to the further degeneration of remaining photoreceptors caused by activated microglia.