The Ahmed glaucoma valve (New World Medical Inc.; Rancho Cucamonga, CA) and the Kuprin valve are commonly used valved drainage devices. The first experience with an Ahmed valve was reported in 1995, and demonstrated the efficacy and safety of its use and effectiveness to prevent hypotony and other complications usually associated with no-valved drainage devices in glaucoma disease 1. Since the 1990s, its use in ophthalmology has significantly increased, especially in glaucoma cases with poor surgical prognosis, such as neovascular and postkeratoplasty glaucoma. Previous studies have shown that valved drainage shunts lower the rate of hypotony, flat anterior chamber,1,2 with appropriate intraocular pressure (IOP) control during the early postoperative period.
Traditionally, the tube has been implanted in the anterior chamber, but the anterior chamber may not be an appropriate site for tube implantation in selected cases such as secondary angle closure, anatomic abnormalities of the anterior segment, patients with low endothelial density, or patients who have previously undergone keratoplasty. Therefore, some authors have reported the insertion of the drainage tube through pars plana into the vitreous cavity2–5 with a success rate comparable with the anterior chamber approach,1,2 including less risk of endothelial damage.
In contrast, many materials have been used to cover the tube such as cadaveric sclera, cadaveric dura mater, fascia lata, bovine pericardium, or amniotic membrane. These biological materials imply a potential risk of contagious diseases; especially infections, such as prion infection,6 viremias, or neoplastic processes which, in addition, are not detected during the donation protocol.7
In addition, scleral sutures can prove to be difficult in certain situations, like high hyperopic eyes (because of small eye size) and scleromalacia and myopia (because of the presence of thin sclera). Furthermore, there are some theoretical complications secondary to scleral sutures which we can prevent using cyanoacrylate instead of classic scleral sutures.
Therefore, we initiated a pilot study using a new suture-less Ahmed valve implantation technique through pars plana with a scleral tunnel in patients with refractory glaucoma.
PATIENTS AND METHODS
Participants, Outcomes, and Analysis
Seventeen patients included in this prospective interventionist study were selected by the Ophthalmology Service of the University La Fe Hospital of Valencia, Spain. All the subjects were aged over 18 years. All the patients presented refractory glaucoma, defined as IOP≥21 mm Hg with antiglaucoma eye drops, with good adherence to treatment, and no previous glaucoma surgery. The study protocol complied with the provisions of the Declaration of Helsinki, and was reviewed and approved by the Ethics Committee of the La Fe University Hospital of Valencia, Spain. Informed consent was obtained from each subject. The mean follow-up was 13.23 months (6 to 28 mo).
The following data were collected and analyzed: patients’ demographic characteristics (age, sex), type of glaucoma, and medical treatment. IOP was measured by Goldman tonometry. Our main study end-point was IOP reduction. Surgical success was based on the definitions by the World Glaucoma Association. Surgical success was defined as IOP≥5 mm Hg and IOP≤21 mm Hg, with or without antiglaucoma medication, and surgical failure was defined as IOP≥21 mm Hg, phthisis, loss of light perception, enucleation, extrusion, mobilization or migration of the tube or the valve, or need for further glaucoma surgery. The paired t test was used to compare preoperative and postoperative IOP; the Wilcoxon test was employed to compare the number of antiglaucoma medications before and after surgery. Finally, Spearman ρ correlation coefficient was utilized to evaluate the association of age and final IOP control.
Surgical Technique and Postoperative Care
All the surgery was performed by the same surgeon (S.G-.D.). All the patients received a model FP7 flexible silicone Ahmed valve (New World Medical Inc.). This valve consists in a 16×13-mm episcleral drainage plate and a tube with an external diameter of 0.64 mm.
Nine patients were at high risk of endothelial failure after Ahmed valve implantation in the anterior chamber (7 postkeratoplasty glaucoma patients and 2 chronic open-angle glaucoma patients with low endothelial cell density). We decided to place the tube in the vitreous cavity, and pars plana vitrectomy (PPV) is mandatory for this purpose.
The other 8 patients were previously vitrectomized. PPV was indicated in 7 patients to treat complications of diabetic retinopathy (5 patients), uveitis (1 patient), and central retinal vein occlusion (1 patient). PPV was indicated in 1 patient with traumatic angle recession because this patient presented a previous traumatic lens luxation.
All the patients underwent PPV 23 G 3-port vitrectomy (1 port for IOP control, 1 port for vitreotome, and 1 port for direct optical control through the microscope) and Ahmed valve implantation. Anterior and central vitreous were thoroughly removed during surgery. Having finished the vitrectomy, the 2 ports used for vitreotome and direct optical control were removed. Afterward, a scleral tunnel was performed from 8.5 to 5.5 mm from the limbus in the superotemporal quadrant just 2 mm behind the superotemporal sclerotomy used for vitrectomy. The valve was purged with saline serum and placed at the superotemporal quadrant. Then the port used for IOP control was removed and the drainage tube was inserted through the superotemporal sclerotomy at 3.5 to 4.0 mm from the corneal limbus. Next, the tube was introduced into the vitreous cavity, making sure it was visible through the dilated pupil. The plate was fixed at 15 mm from the corneal limbus with cyanoacrylate at the superotemporal quadrant. Once surgery had been completed, the conjunctiva was closed with 2 drops of cyanoacrylate placed on the sclera (Fig. 1).
The starting time was considered when three 23-G ports were inserted or when the conjunctiva was opened if the patient had been previously vitrectomized.
Topical antibiotics (tobramycin 4 times a day), steroids (prednisolone acetate every 2 h that tapered over 1 mo), and cycloplegics (cyclopentolate 3 times a day) were prescribed for the 4 postoperative weeks. Patients’ follow-up examinations were performed at 1 day, 1 week, 1 month after surgery, and then every 2 months.
The mean age was 57.70 years (range, 40 to 81 y). Ten patients were female. The underlying pathologies were proliferative diabetic retinopathy (5 cases), central retinal vein occlusion (1 case), angle recession (1 case), uveitis (1 case), refractory open-angle chronic glaucoma (9 cases), and postkeratoplasty glaucoma (7 cases). Table 1 lists the cases’ characteristics.
The mean follow-up time was 13.23 months (range, 6 to 28 mo). A total of 10 patients (58.82%) completed the 12-month follow-up, 4 patients (23.53%) the 18-month follow-up, and 3 patients (17.64%) the 24-month follow-up. We performed a Kaplan-Meier survival analysis of surgical success and follow-up (Fig. 2). Success was achieved in 15 cases (82.20%), with optimum IOP control without medical treatment in 8 cases (47.06%). The success rate according to the follow-up is provided in Table 2, and we have drawn a box-plot to show the IOP results (Fig. 3).
The mean surgical time was 9.76±2.60 minutes, and was 6±0.81 minutes in patients with previous vitrectomy (4 cases). The mean preoperative IOP was 37.64±8.41 mm Hg, the mean postoperative IOP was 16.71±7.49 mm Hg at the last visit for all patients, and was 14.40±3.26 mm Hg for patients with successful surgery; there was a significant statistical difference (P<0.0001). Indeed, the mean preoperative IOP was significantly higher than all the mean postoperative IOPs of all the follow-up visits (P<0.001) (Table 1 and Fig. 3). Visual acuity was stabilized and there was no statistical difference between preoperative visual acuity and postoperative visual acuity (P=0.26). The average number of antiglaucoma eye drops used was 2.88±0.33 preoperatively and 0.76±0.97 postoperatively (P<0.0001) (Table 1).
Ahmed valve implantation and antiglaucoma eye drops were not sufficient to achieve a good final IOP control in 2 patients (11.76%). Therefore, trabeculectomy was performed in both these patients. Two patients presented (11.76%) blockage of the drainage tube by vitreous; this obstruction was treated with Nd:YAG (1 case) and second vitrectomy (1 case). There was no case of migration or mobilization of either the tube or the plate, and neither extrusion of the tube nor phthisis bulbi was reported during the follow-up. No intraoperative complication was noted. The most common postoperative complication was dysesthesia, observed in 6 cases (35.29%), which was easily controlled with diclofenac eye drops. Mild vitreous cavity hemorrhage occurred in 3 patients (17.65%), whereas no choroidal effusion, corneal edema, retinal or choroidal detachment, or hypotony were noted. We did not observe any important inflammatory reaction due to cyanoacrylate. Table 3 lists the complications observed during the follow-up.
A hypertensive phase occurred postoperatively in 7 patients (41.17%) by a mean of 5.80 weeks. The hypertensive phase responded to medical therapy in all the patients.
There was a negative low correlation (r’s=−0.35) between patients’ age and final IOP control (r’s=0.29).
Our technique is merely an evolution of the classic pars plana Ahmed valve implantation, yet offers us the possibility of cutting the surgical procedure time. In addition, it lowers the risk of potential complications because of both scleral sutures and the use of biological graft patches to cover the tube. There was no migration, mobilization, or extrusion of the tube (Table 3), and the IOP control results were similar to other techniques reported in the literature (Tables 1 and 4; Fig. 3).
The use of biological donated graft patches implies a potential low risk of contagious diseases, such as prion infection,6 viremias, or neoplastic processes, which were not detected during the donation protocol.7 With the creation of an autologous scleral tunnel, we prevented this potential low risk of infection secondary to the use of biological materials, as well as the risk of secondary infection due to tube erosion and extrusion.
The suture-less option with cyanoacrylate has proved to be an effective method for fixing the plate during the follow-up. However, it implies some theoretical risks, such as mobilization or migration of the plate or the tube. Despite this, we did not observe these adverse effects during the follow-up (0 patients in 13.23 mo, range 6 to 28 mo).
No severe adverse effects were observed during the study, except for mild dysesthesia (35.29%). We think dysesthesia is related directly to surgery because it appeared during the immediate postsurgical period and was easily controlled with diclofenac eye drops. Although the study did not show any adverse events associated with our surgical technique, the study sample size is too small to determine its complete safety. Indeed, the limitations of this study are its small sample size and lack of a control group. In the future, we will conduct a larger controlled study to compare the classic pars plana approach with scleral sutures and the suture-less technique.
This surgery usually requires 9.76±2.60 minutes (PPV and Ahmed implantation), and 6±0.81 minutes (only Ahmed implantation in previously vitrectomized patients). The same surgery lasts approximately 25 minutes for PPV and Ahmed implantation with donor cadaveric tube coverage, and 20 minutes for Ahmed implantation with donor cadaveric tube coverage in previously vitrectomized patients. The main advantages of this approach are: first, this technique is easier and more repeatable; second, it is faster than the classic pars plana approach; furthermore, we prevent other possible complications due to scleral sutures, such as ocular perforation and sutures intrusion.
Ocular perforation usually occurs during the intrascleral passage of needles and may involve the sclera, the choroid, or the retina. The odds of this event are very low, and in most cases scleral perforation is undetected at the time of surgery, however, is discovered later given the presence of a chorioretinal scar or subretinal fluid, which may represent deep choroidal involvement rather than actual retinal perforation; or is even detected by sympathetic ophthalmia long after perforation.18,19 Intrusion of sutures into the eye has been reported only as an adjunct to buckle intrusion, yet it is another possible theoretical complication of scleral sutures.20
No glaucoma drainage tube kink after pars plana insertion was noticed either intraoperatively or postoperatively, although we did not use the pars plana clip. Other authors have reported this complication and its management with pars plana clips.21 An autologous scleral tunnel prevented tube extrusion without the use of biological graft patches. Furthermore, previous studies have reported a variable complication rate, which we did not note in our technique: early hypotony in up to 30% of cases,10 transient choroidal detachment in up to 43%, retinal detachment or recurrent vitreous hemorrhage in up to 30%.3,4
Thus, our suture-less pars plana Ahmed valve implantation is effective in our case series. No severe adverse effects were observed during the study, except for mild dysesthesia (35.29%). However, a longer follow-up and more patients are needed to confirm our observation.
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