Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Diabetic Retinopathy ?
    ### Response:
    The four stages of diabetic retinopathy are - mild nonproliferative retinopathy  - moderate nonproliferative retinopathy  - severe nonproliferative retinopathy  - proliferative retinopathy mild nonproliferative retinopathy moderate nonproliferative retinopathy severe nonproliferative retinopathy proliferative retinopathy Nonproliferative retinopathy.
    