Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Refractive Errors ?
    ### Response:
    The cornea and lens of your eye helps you focus. Refractive errors are vision problems that happen when the shape of the eye keeps you from focusing well. The cause could be the length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens.
    