JJ Lee, et al. AHMED VALVE WITH TUBE LIGATION AND STENTS 6 mmHg.5,8-12 In previous studies, suprachoroidal hemorrhage occurred in 1.7% to 4.7% of AGV implantations.5,8-12 This has been explained by valve failure, leakage around the tube, or a decrease in aqueous production.13,16 Of these possible causes of early postoperative hypotony, leakage around the tube is now prevented by corneal puncture using a 23-gauge needle.5 Kee13 used partial ligation of a silicone tube with 8-0 Vicryl in AGV, to restrict aqueous humor flow.13,14 He showed that the early postoperative hypotony and its surgical compli- cations are less frequent if the AGV tube is partially ligated, but differences between the ligation and non-ligation groups were not statistically significant in his study, probably because of a small sample size.13 In the previous partial ligation study, the operator ligated both the tube and a stent (6-0 Prolene) with 8-0 Vicryl and then removed the stent. In the present study, the ligation of the AGV silicone tubes with 8-0 Vicryl was done in combination with the use of 3 strands of 8-0 Nylon as external stents. We did not remove the stents intraoperatively (complete ligation). We decided when to remove the stents according to the post- operative IOP. When IOPs failed to reduce postoperatively, stents were removed early to increase internal tube diameters. This method may have advantages compared to the previous partial ligation method in that IOP control is easier and more adjustable because the time of stent removal can be decided according to the postoperative state. The stents were simply removed with a forceps under a slit lamp because they remained exposed to the conjunctival surface. Moreover, stent removals during the immediate postoperative period were accompanied by rapid and sufficient IOP reductions, which suggest that enlargement of the tube lumen induces enhanced outflow and subsequent IOP reduction. The disadvantage may be irritation due to the external stents, however, this can be minimized by ensuring an adequate length of the 8-0 Nylon strands so as not to touch the cornea and removal within one month in most cases. There were two reasons for using three strands of 8-0 Nylon as external stents rather than one large single strand. One was to reduce conjunctival irritation because one thick suture creates a greater sense of a foreign body than three thinner strands. The second reason is that they were originally intended to allow high postoperative IOP adjustment by removing them one by one. During the course of the study they were removed en bloc in most cases for fast IOP control; however, in two cases where stents were serially removed, additional stent removal resulted in additional IOP reduction, suggesting the advantage of multiple thin external stents. We have to consider the reason for the occasional lack of a postoperative day one IOP spike despite the complete ligation of the tube. One possibility is that complete ligation was not performed in all cases because there might have been a minute space open inside the lumen of the ligated tube, or there is a possibility that there might be a flow of aqueous through the space between the tube and the corneoscleral ostium in the early postoperative period. As a result of ligation and external stenting, 3 eyes (3.2%) showed an IOP of <5 mmHg on the first postoperative day. All hypotonic eyes recovered to the normal range within 2 weeks. A total of 6 eyes (6.3%) had a shallow anterior chamber on the first postoperative day in this study. We had no ex- perience of flat or shallow anterior chambers that required surgical chamber reformation during the course of the study, and no suprachoroidal hemorrhage occurred. A choroidal effusion occurred in one eye with congenital glaucoma and an IOP of 6 mmHg on the first postoperative day, but this spontaneously regressed and did not require surgical inter- vention. Molteno and Dempster14 reported a transient IOP ele- vation following a short-lived HP after single-plate Molteno implant surgery. This HP has been also reported for AGV implantation.4,9,10 The HP appeared approximately 4 weeks after surgery and lasted for at least 12 to 16 weeks. This phase is caused by histological changes in the bleb around an implant end-plate related to the formation of a layer of fibrous tissue in the bleb after diffuse edema and congestion disappears. The fibrotic capsule formed is resistant to aqueous flow, and thus results in an IOP elevation.13,16,17 In the current study, it was found that the HP appeared after an average of 2.7±1.5 weeks in 49 eyes (51.6%), the occurrence of the HP could not be ascertained in 25 eyes (26.3%) due to the use of medications. The mean highest IOP in those with a HP was 29.8±6.9 mmHg. The mean IOP profile also started to increase between 1 and 2 weeks after a fall in IOP on the first postoperative day. The mean IOP peaked from 2 weeks to 1 month postoperatively, and then stabilized over the ensuing months. Although the HP occurred earlier than in previous studies, the incidence of a HP and the mean highest IOP in those that developed a HP were similar to those reported for conventional AGV implant surgery. Tube ligation and external stent placement did not affect the HP, except for the time of occurrence. This is believed to be caused by an early IOP elevation due to the tube ligation. In this study, the mean number of anti-glaucoma medications was larger at 1 month postoperatively (1.5±1.2) than has been reported previously (0.4 to 0.82), though the mean medi- cation number at 1 year postoperatively was similar to those of other studies.9,10 An early increase in medication is also related to the early appearance of the HP. The cumulative probability of success at 1 year was 84.2% in the present study, which compares favorably with the success rates reported by previous studies (70% to 87%),8,13-16,18,19 although some of the criteria used to measure success differ between studies. Our study has the limitation that it is not a prospective, randomized, controlled trial. Despite its limitations, no other review has been conducted on the long-term follow-up data of a large number of patients that have undergone AGV implantation with tube ligation and external stents. In conclusion, AGV implantation with tube ligation and 91