Fig. 48. A Case of a failed filtering bleb. In filtration surgery, the fistula created must remain open to be of benefit to the patient. The natural tendency of the wound healing process is to close this fistula by forming fibrous tissue that will contract and close the wound. In this case, the degree of opacification indicates that a large amount of fibrous tissue has formed and that this bleb is or shortly will be nonfunctional.