Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Keratoconus ?
    ### Response:
    Keratoconus is the degeneration of the structure of the cornea, which is the clear tissue covering the front of the eye. In this condition, the shape of the cornea slowly changes from the normal round shape to a cone shape. Most people who develop keratoconus start out nearsighted, which tends to become worse over time.
    