Which Disease Cause Early Morning Blindness And Impaired Vision?

My sister was diagnosed with a disease that causes early morning blindness, and impaired vision later in the day. Salt was the problem and she had to use drops in the morning to help neutralize it?? She was supposed to apply for the state to do surgery on her eyes to permanently fix this, but our state is currently not taking care of the poor, so she is waiting for total blindness. Now my mother is thinking of paying for the surgery, but we don t know what the name of the disease is, so that we could check the price.