FILTERING SURGERY ALONE
When the glaucoma is uncontrolled despite maximum tolerable medical therapy and laser trabeculoplasty, the surgical procedure of choice is the one that has the greatest chance of providing long-term IOP control. In most cases, this is a filtering operation performed alone. In some patients, eliminating the need for IOP lowering therapy postoperatively may improve the quality of life and vision enough to delay the need for cataract surgery. In other cases, the cataract can be removed 4 to 6 months later, once the filtering bleb is well-established, as the second part of a two-stage approach. In one study, patients who underwent the two-stage procedure had a greater percentage of long-term IOP reduction than those who had cataract surgery alone or a combined cataract-glaucoma operation (15). Other studies have revealed that results of the two-stage procedure versus combined phacoemulsification and trabeculectomy are similar (37,38). In a study of 21 patients undergoing ECCE with posterior chamber lens implantation in eyes with established filtering blebs, followed for a minimum of 2 years, the IOP rose an average 3.5 mm Hg, with six eyes requiring resumption of medical therapy and two requiring repeat filtering surgery (39). Phacoemulsification via a clear cornea incision is likely to improve these results. Temporal clear corneal phacoemulsification did not cause a significant difference in IOP control in patients with filtering blebs after one year of follow-up in one study (40). In another study, phacoemulsification through a superior clear corneal incision in eyes with previous trabeculectomy increased the IOP within one year, but at two years there was no significant difference from baseline in IOP control (41). Retrospective studies have shown that in patients with glaucoma who had trabeculectomy and subsequent cataract surgery, the IOP appeared to be better controlled by phacoemulsification than by ECCE (42,43). However, the bleb is still likely to become smaller and IOP is likely to increase even after phacoemulsification, especially if the preoperative IOP is greater than 10 mm Hg, there is intraoperative iris manipulation, and the patient is younger than 50 years old (44,45). IOP usually increases after phacoemulsification in eyes with preexisting hypotony (46), but resolution of the hypotony is unpredictable (45).
