Has the vet tried to do a culture and sensitivity of the eye. If it is infection and you aren't using an antibiotic the bug is sensitive to you won't eliminate it completely. You might be knocking it down with the terramycin but not enough to kill it completely. If that is the case replacing the wrapping of your branches or disinfecting could prevent reinfection.
An other thought would be to examine a smear of the eye discharge under the microscope or submit it for cytology (examination of the cells).
An other thought would be to examine a smear of the eye discharge under the microscope or submit it for cytology (examination of the cells).