Glaucoma drainage implants are shown to be successful in IOP reduction. When target IOP is not achievable with medical therapy or laser, glaucoma drainage implants should be chosen especially in secondary glaucoma in spite of the risk of complication because glaucoma ends up in irreversible blindness.
Although IOP can be successfully managed after AVI, posterior segment complications may develop. It is significant to understand the possible postoperative complications of AVI to maximize surgical efficacy. However, posterior segment complications of AVI have not been described in detail previously. In previous studies, rates of retinal complications were from 14 to 50% for the Molteno implant, 35% for the Krupin-Denver valve, 38–40% for the Krupin valve with a disc, and 22–48% for the Baerveldt implant [7,8,9]. Comparing these studies is hard due to different follow-up periods, different patient populations, small sample size, different surgical techniques, and different criteria for diagnosis. Our study involved a large sample size of eyes and the incidence of posterior segment complications of AVI was 31.4%.
The TVT study compared the efficacy of glaucoma drainage implant to trabeculectomy [4, 5]. The rate of postoperative complications was 34% during the first year which was similar to our study. The cumulative probability of failure was 29.8% in the tube group at 5 years [4, 5]. However since the Baerveldt implant was used in the TVT study, it’s difficult to accurately compare the results with ours. In the Ahmed Baerveldt Comparison Study, hyphema was the most common complication, accounting for 79% of intraoperative complications and no patient suffered an intraoperative suprachoroidal hemorrhage [10]. In the Ahmed Versus Baerveldt study, the complication rate was 52% in the Ahmed group which was higher than our results. The choroidal effusions accounted for 13%, which is similar to our study [11, 12].
Choroidal detachment, which also accounted for large proportion of posterior segment complication in our study, the incidence was 17.7%. In the TVT study, the incidence of choroidal effusion was 14% in tube which was similar to our results [5]. Another study reported 10% of choroidal effusion in Baerveldt valves and 15% in Ahmed valves [13]. The reported incidence of hypotonic maculopathy is 1.3–20% after glaucoma surgery [14]. We showed 2.0% of postoperative vitreous hemorrhage after AVI. Vitreous hemorrhage might have been a complication of the AVI, although contribution of underlying conditions could not be perfectly ruled out. Law et al. showed 5% incidence of vitreous hemorrhage after aqueous shunt placement [15]. The hemorrhage may result from, deep sclera sutures, bleeding from posterior segment conditions like suprachoroidal hemorrhage, or extension of bleeding from shunt entrance wound and iris neovascularization.
The reported incidence of suprachoroidal hemorrhage is 0.6–1.5% after trabeculectomy and 0.5–8.3% after shunt procedures [16]. In our study, intraoperative and delayed suprachoroidal hemorrhage was recognized in 1.2% which was similar with previous studies. Risk factors are high myopia, severe postoperative hypotony, high preoperative IOP, pseudophakia, aphakia, pulmonary disease, ischemic heart disease, systemic hypertension, and anticoagulation [17]. In our study, patients informed of their coughing prior to the onset of suprachoroidal hemorrhage. The visual prognosis was seriously bad, therefore, managing IOP, controlling risk factors, and monitoring of INR can decrease the risk for suprachoroidal hemorrhages after AVI.
The reported incidence of infectious disease after glaucoma surgery is 0.12–1.3% for endophthalmitis, 0.55–2.6% for blebitis [18, 19]. The endophthalmitis after AVI was reported to show more insidious onset than after cataract surgery and late-onset cases may develop after months to years due to infection through tube exposure [20]. Bacterial strains in endophthalmitis after AVI were reported to be more virulent, and showed high percentage of streptococcus species [21]. The incidence of retinal detachment was 1.2% in our study. Previous study revealed 5% incidence of retinal detachment after Molteno implant surgery, developing within 4 months following surgery [22].
Mermound et al. and Sidoti et al. found that preoperative VA worse than 20/200, diabetic retinopathy as cause of neovascularization, and young age were significantly associated with surgical failure for neovascular glaucoma in Molteno and Baerveldt shunt surgery [23, 24]. However, those authors did not separately assess IOP control and visual acuity in patients with posterior segment complications. In our study, older age, postoperative hypotony, and hypertension were found to be associated with posterior segment complications of AVI. Hypertension increases the fragility of vasculature and disrupts the integrity of the choroidal vasculature, that eventually lead to increased permeability [25, 26]. The structural vulnerability of the microvasculature, intraoperative or postoperative blood flow fluctuation may result in posterior segment complications in the old aged patients. The hypotony in postoperative period contributes to choroidal effusion and it causes a mechanical stress on the posterior ciliary artery which may result in suprachoroidal hemorrhage [27, 28]. Haga et al. showed that older age and postoperative hypotony were risk factors for choroidal detachment [29]. The results shown in our study are consistent with previous studies.
This limitation of our study is that the study was conducted by a retrospective design. However, we reported the most significant representation of postoperative posterior segment complications of AVI, both in regards to duration of follow-up and number of eyes. Our study quantified the long-term complication rates that can reshape surgical armamentarium and improve the quality of treatment of glaucoma.
