Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Fuchs endothelial corneal dystrophy ?
    ### Response:
    Fuchs endothelial corneal dystrophy (FECD) is an eye disease. It affects the thin layer of cells that line the back part of the cornea. This layer is called the endothelium. The disease occurs when these cells slowly start to die off. The cells help pump excess fluid out of the cornea.
    