Even with some therapies, the IOP is often increased to an uncontrolled level, sometimes leading to blindness. According to a systematic review and meta-analysis of comparative studies of two or more surgical techniques (one of which had to be trabeculectomy), including patients with open-angle glaucoma, trabeculectomy still offers the possibility of obtaining excellent IOP control at the long-term follow-up in patients with open-angle glaucoma , whereas the success rate of trabeculectomy for NVG is still poor . In the present study, the survival rate of trabeculectomy for NVG was 83.7% after 6 months, 70.9% after 12 months, and 60.8% after 24 months.
Several previous studies investigated the success rate of trabeculectomy with MMC for NVG. One study reported that the cumulative probability of the success of trabeculectomy was 67.0% after 1 year and 61.8% after 2 to 3 years . According to another report, the probability of success at 120, 240 and 360 days after combined preoperative IVB and trabeculectomy was 87.5%, 79.2%, and 65.2%, respectively, but the corresponding values after only trabeculectomy without IVB were 75.0%, 71.9%, and 65.3%, respectively . Our surgical outcomes in the present study are similar to these reports.
Although there was a trend for less failure in the IVB group until postoperative 23 months, preoperative IVB finally did not significantly improve the outcome of trabeculectomy with MMC for NVG in our study. Moreover, it did not decrease the risk of postoperative hyphema. Sugimoto et al. , using resected irises from NVG patients during trabeculectomy, reported that IVB reduced the neovascularization on the iris surface but could not completely eliminate neovascularization in the iris stroma. They also reported that IVB did not prevent postoperative complications at 1 day after trabeculectomy, including hyphema . Takihara et al., performing IVB 1 to 5 days before the trabeculectomy for NVG patients, reported that preoperative IVB did not significantly improve the surgical outcomes, in common with our study .
In contrast, Saito et al. reported that preoperative IVB decreased postoperative hyphema and increased the surgical success rate . The discrepancy between these studies may be due to the different intervals between the IVB and the trabeculectomy: in the Sugimoto study and Takihara study, they performed the IVB 6 to 8 days and 1 to 5 days before the trabeculectomy, respectively, whereas in the Saito study, the IVB was performed 10 ± 11 days before the trabeculectomy. In our study, the IVB was performed 3.6 ± 1.8 days before the trabeculectomy, and the results are consistent with the Sugimoto study and Takihara study. Considering these data, using a sufficiently long interval between the IVB and trabeculectomy may be more effective by calming down the activity of neovascularization in the anterior segment.
Another study demonstrated that NVG eyes with a history of vitrectomy had poor surgical outcomes after trabeculectomy . Vitrectomy exacerbates retinal ischemia and increases the concentration of inflammatory cytokines and/or VEGF in the anterior chamber . Our present analysis did not find that previous vitrectomy is a prognostic factor. Thirty eyes had already undergone a vitrectomy before trabeculectomy, and 25 eyes underwent a vitrectomy concurrently to receive more photocoagulation to the extreme periphery of the retina intraoperatively. Additional photocoagulation may improve retinal ischemia; here it may have led to the satisfactory surgical outcomes. Moreover, some reports indicated that younger NVG patients have a poor success rate following trabeculectomy , but in the present study we found no significant difference in the surgical outcome between patients under 50 years old (14 eyes) and those ≥ 50 years old (35 eyes). This may be because there were many more patients over 50 years old in our study.
Trabeculectomy in NVG patients usually results in frequent postoperative complications and poor surgical outcomes. Hyphema has been described as the most frequent postoperative complication of trabeculectomy in NVG patients . However, there is no report that postoperative hyphema significantly influences the surgical outcome of trabeculectomy with NVG. In the present study, hyphema was the most common postoperative complication, and we also found that postoperative hyphema was a significant prognostic factor in trabeculectomy for NVG. Moreover, patients with PDR were found in another study to have significantly higher serum levels of cytokines such as interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α and VEGF compared to non-PDR patients . The serum levels of TNF-α, IL-6, and C-reactive protein (CRP) were also higher in subjects with arteriosclerotic peripheral vascular disease compared to healthy controls .
TNF and IL-1 were reported to be capable of stimulating the proliferation of Tenon’s capsule fibroblasts . Moreover, Cvenkel et al. indicated that lower levels of TNF-α and IL-6 in the aqueous humor were associated with better surgical outcomes in patients undergoing trabeculectomy . Tripathi et al. reported the results of an intracameral injection of tissue plasminogen activator in the anterior chamber for eyes with fibrin clots and elevated IOP after glaucoma filtering procedures ; soon after the injection, the fibrin clots dissolved completely and the elevated IOP values decreased to the normal level. Tripathi et al. suggested that fibrin clots after filtering surgery provide a scaffold for the formation of scar tissue in the anterior chamber and in the fistulization tract.
In view of these reports, when hyphema occurs after trabeculectomy, increased concentrations of some cytokines may lead to a failure of conjunctival bleb formation. Additionally, blood flow into the trabecular meshwork may lead to a stronger wound-healing response or clog the flow of aqueous humor, but further study is required to test this notion.
There are a few reports about reducing the incidence of hyphema following trabeculectomy. Wilson et al. reported that during trabeculectomy, filling the anterior chamber with sodium hyaluronate reduced the incidence of postoperative hyphema for glaucoma patients with primary open-angle glaucoma, chronic angle closure glaucoma, congenital glaucoma, or NVG ; they suggested that the reduced incidence was due to a microvascular clotting effect or the tamponade of higher intraocular pressure. To avoid unfavorable hyphema, Elgin et al. used direct cauterization of the iris before iridectomy, and they reported that this protocol effectively reduced the rate of intraoperative bleeding and postoperative hyphema in trabeculectomy for NVG . The direct cauterization of the iris seeking to reduce postoperative bleeding may be a beneficial new procedure for better prognosis in NVG patients.
In addition, as a new glaucoma surgery, the Ex-PRESS drainage device was introduced in 2011 as an alternative to trabeculectomy . During this operation, iridectomy is not required, and thus hyphema is less likely compared to the use of trabeculectomy. The results of our present retrospective study indicate that postoperative hyphema could be a surgical risk factor for failure of trabeculectomy in NVG, but in light of the study’s retrospective nature, further prospective randomized investigations are required. Filling the anterior chamber with ophthalmic viscosurgical devices intraoperatively, the direct cauterization of the iris, or the use of the Ex-PRESS drainage device may provide better prognoses in NVG patients.