To shed light on microglia activation and to test whether microglia and macrophages are distinguishable in retinal degeneration, c-mer proto-oncogene tyrosine kinase (Mertk)−/−Cx3cr1GFP/+Ccr2RFP/+ or Mertk+/+Cx3cr1GFP/+Ccr2RFP/+ mice were established by breeding Mertk−/−, Cx3cr1GFP/GFP, and Ccr2RFP/RFP mice. The gene discussed is MERTK; the disease is retinal degeneration.