Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) retinitis pigmentosa ?
    ### Response:
    Retinitis pigmentosa is a group of related eye disorders that cause progressive vision loss. These disorders affect the retina, which is the layer of light-sensitive tissue at the back of the eye. In people with retinitis pigmentosa, vision loss occurs as the light-sensing cells of the retina gradually deteriorate.
    