Corneal endothelial failure is a well-known complication after AC tube shunt placement [2, 3]. To minimize the corneal endothelial cell loss after GDD implantation, ciliary sulcus can be considered as a potential space for the tube shunt placement, especially in eyes with shallow AC depth or compromised corneal endothelium. Ciliary sulcus tube shunt implantation was first described by Rumelt and Rehany and they performed this procedure in 3 glaucoma patients who had previous corneal transplant surgery . In these 3 patients ciliary sulcus insertion of the tube was performed by the authors owing to the combination of pseudophakia or aphakia, corneal graft and moderate shallowing of the AC. They used AGV in two eyes and Molteno implant in one eye. During the mean follow-up of 18 months, IOP readings were found to be in normal level (range, 8–14 mmHg) without any antiglaucomatous medication and corneal grafts remained unchanged. Authors suggested this surgical approach in pseudophakic or aphakic eyes with primary corneal diseases (i.e., Fuchs endothelial dystrophy), corneal transplants, shallow anterior chamber or extensive synechial angle closure. After their publication, this surgical technique has been supported by various studies and case reports in the literature [11–18]. In the present study, we investigated the clinical outcomes of AGV tube implantation into the ciliary sulcus in our patients and our short-term results showed that ciliary sulcus implantation of the tube shunt was a safe and effective procedure. Our overall success rate at final visit was found as 87.2 % and that was comparable with the previous studies related to ciliary sulcus tube shunt implantation in which success rates were reported between 78.6% and 100 % [12–14, 17, 18]. However, direct comparison of the results of different studies is imprecise due to the differences in the distribution of glaucoma diagnosis, follow-up periods, definition of success criteria and implanted GDD type. In one of these studies, Eslami et al.  reported the outcomes of the AGV tube implantation into the ciliary sulcus in aphakic and pseudophakic eyes. They evaluated 23 eyes of 23 patients retrospectively with the mean follow-up period of 9 months (range, 3–24 months). In their study, IOP reduced from 37.9 ± 12.4 mmHg to 16.2 ± 3.6 mmHg at last follow-up visit and they achieved a success rate of 78.6%. Reported serious complications were endophthalmitis (one eye), tube exposure (one eye) and vitreous tube occlusion (one eye). Authors concluded that placement of the tube in the ciliary sulcus was a safe and effective procedure. Bayer et al.  conducted a retrospective study comparing the efficacy and safety of AC angle (68 eyes) vs ciliary sulcus (35 eyes) placement of AGV tube. They reported no difference in success rates (success rate was 85.3 % in the ciliary sulcus group with a mean follow-up period of 30.2 ± 17.7 months and 83.8% in the AC angle group with a mean follow-up period of 27.2 ± 16.5 months). Although they found the mean IOP and the number of glaucoma medications at final visit similar in both groups, IOP reduction ratio was found to be higher in the ciliary sulcus insertion group. They could not provide an explanation for this difference between the groups, but they proposed that, decrease in secretion of aqueous in the ciliary sulcus insertion group due to mechanical or toxic effects of the silicone tube on the ciliary body might have been the cause.
Like previous reports, hyphema was found to be the most frequent (24.3%) postoperative complication in our study. Hyphema was mostly encountered in eyes diagnosed with neovascular glaucoma and all hyphemas resolved spontaneously within one month. In Bayer et al’s study the incidence of hyphema was found as 17.6% in the AC group and 14.3% in the ciliary sulcus group and they reported no differences between the groups . Weiner et al.  implanted Baerveldt-350 tube shunt into the ciliary sulcus in 36 pseudophakic eyes and they found a high rate of hyphema (27.8 %) compared to TVT study (%2) in which Baerveldt-350 tube shunt was implanted into the AC. Authors attributed this high rate of hyphema due to the more vascularized tissues of the ciliary sulcus compared with the angle or pars plana.
Progressive corneal endothelial cell loss and eventual corneal decompensation is a well-known complication of AC tube shunt procedures [3–5, 19, 20]. The rate of corneal complications after AGV implantation was reported as high as 16–27% in previous reports and the risk was found to be higher in eyes with corneal graft [6, 20–23]. The exact mechanism of corneal endothelial cell loss after the tube shunt surgery has not been fully understood, but intermittent tube-corneal contact (by eye rubbing, squeezing, and even blinking), tube-uveal touch, turbulence present at the tip of the tube, chronic inflammation and foreign body reaction to the silicone tube itself are the proposed mechanisms [3, 4, 24]. Postoperative complications such as flat AC or constant tube-corneal touch may also cause corneal endothelial cell damage. Placing the tube in the AC, especially in eyes with shallow anterior segments, promotes tube – corneal touch, but ciliary sulcus placement of the tube makes this possibility quite remote. So, in eyes with shallow AC, we preferred to insert the silicone tube into the ciliary sulcus instead of the AC angle. We did not observe constant tube-corneal touch in any eye during the follow-up period. A final visit, corneal decompensation was not seen in any eye with preoperative clear cornea, but it should be noted that our follow-up period was short. Studies evaluating the corneal endothelium in eyes with AC tube shunts have shown that there is a constant insult to the corneal endothelium near the silicone tube and it has been suggested to place the tube as far from the cornea as possible to protect the corneal endothelium [4, 24]. In another study, endothelial contact at the insertion point of the tube was proposed as a risk factor for corneal endothelial cell loss in AC tube shunt surgery and authors recommended entry site of the tube to be posterior to Schwalbe’s line to avoid corneal endothelial trauma . In this regard, ciliary sulcus implantation of the tube shunt seems to be more confident for the corneal endothelium than AC angle. Currently, in aphakic/pseudophakic eyes with corneal graft or compromised corneal endothelium, ciliary sulcus is our priority choice for the tube placement to protect the corneal endothelium. Weiner et al.  implanted Baerveldt glaucoma implant in the ciliary sulcus of the 36 eyes in which there was high risk of corneal decompensation like shallow anterior chamber, corneal graft, corneal guttata, or corneal edema. During the mean follow-up period of 21.8 ± 16.6 months, corneal decompensation was observed in only one eye with preoperative clear cornea. So that the authors stated that the tube insertion through the ciliary sulcus during GDD surgery was a safe and effective procedure. In another study with a mean follow-up period of 37.2 ± 18.9 months, Prata et al.  reported no case of postoperative corneal decompensation or graft failure in 17 eyes underwent ciliary sulcus Baerveldt glaucoma implant. Ciliary sulcus is also our priority choice for the tube placement in aphakic/pseudophakic eyes with extensive peripheral anterior synechiae like neovascular glaucoma. In eyes with extensive peripheral anterior synechia, sometimes it is very difficult or even inapplicable to insert the tube properly through the iridocorneal angle into the AC. Moreover, in a previous report, presence of the peripheral anterior synechiae was proposed as a risk factor for the corneal endothelial cell loss . Although ciliary sulcus tube shunt placement seems to be safe for corneal endothelium, to our knowledge, no study has examined corneal endothelial cell change after ciliary sulcus tube shunt placement to date. Future studies with specular microscopy evaluating progression of corneal endothelial cell changes in eyes that underwent ciliary sulcus tube shunt placement will be more informative in this regard.
In the past, pars plana tube insertion with complete pars plana vitrectomy had been advocated in eyes where AC tube insertion could not be possible or ideal [7–10]. Although it has been shown as an effective procedure, pars plana insertion may lead to significant posterior segment complications such as retinal break, retinal detachment, vitreous hemorrhage, epiretinal membrane formation and even blindness. Furthermore, tube blockage also reported after pars plana implantation due to residual vitreous . Along with posterior segment complications, pars plana approach adds additional cost and extends the operation time also. Ciliary sulcus insertion is more simpler, time saving and less invasive procedure compared to pars plana insertion. Thus, we can say ciliary sulcus implantation seems to be more advantageous than pars plana implantation.
It can be considered that ciliary sulcus tube shunt placement may cause chronic intraocular inflammation or pigment release due to the close contact between the tube and the iris. We did not notice an abnormal intraocular inflammation, posterior synechiae formation or pigment dispersion during the follow-up period in any eye. Also in the previous reports, generally, marked inflammation or pigment dispersion has not been mentioned after ciliary sulcus tube shunt implantation. However, Bayer et al.  reported marked postoperative intraocular inflammation in one of their 3 uveitic glaucoma patients underwent ciliary sulcus tube shunt placement.
In the current study, in the follow-up period, tube obstruction developed in two patients and it was due to vitreous incarceration into the tube opening. These two patiens had aphakic glaucoma. Aphakia can be considered as a contributing factor in emerging of this complication. The presence of the IOL serves as a barrier against forward movement of the vitreous gel. However, it should be noted that, vitreous incarceration after ciliary sulcus tube shunt placement has also been reported in pseudophakic eyes without an intact posterior capsule . In our study, there were 6 eyes diagnosed with aphakic glaucoma. Although vitreous was not seen in the AC or pupillary area in any of them during the surgery, increase in IOP occurred in 2 eyes during the follow-up period due to vitreous incarceration. Tube obstruction was releived successfully with anterior vitrectomy in both eyes.
Limitations of our study include retrospective study design, short follow-up period, non-availability of the corneal endothelial cell density data and the lack of control group. However, the major strength of our study is the sample size. To the best of our knowledge, current study is the largest series in the literature in respect of ciliary sulcus AGV implantation.