Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Retinochoroidal coloboma ?
    ### Response:
    Retinochoroidal coloboma is an eye abnormality that occurs before birth. It is characterized by missing pieces of tissue in both the retina (the light-sensitive tissue lining the back of the eye) and choroid (the blood vessel layer under the retina). In many cases, retinochoroidal coloboma does not cause symptoms.
    