Experience with early internal obstruction of the filtration site following filtration surgery.

Most failures of glaucoma filtration surgery are due to external scarring of the bleb site because of proliferation of Tenon's capsule.' This failure can occur any time from weeks to years after the surgery, although more commonly within the first 3 months. It usually is a gradual process with progressive shrinkage of the bleb size and height. Occasionally, however, loss of the bleb can occur acutely during the early postoperative period, and in some of these cases, failure of the surgical procedure may be due to internal blockage of the filtration site by iris, ciliary processes, vitreous, or inflammatory debris. Over the years, we have encountered a number of such cases, and experience has suggested that with prompt intervention, we have been able to restore filtration and preserve bleb function in most of these eyes. We decided to investigate these patients to see if there were any factors that seem to predispose these eyes to this type of problem and to see if we could learn any lessons about their management.