Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) cone-rod dystrophy ?
    ### Response:
    Cone-rod dystrophy is a group of related eye disorders that causes vision loss, which becomes more severe over time. These disorders affect the retina, which is the layer of light-sensitive tissue at the back of the eye. In people with cone-rod dystrophy, vision loss occurs as the light-sensing cells of the retina gradually deteriorate.
    