Evaluation of the New Glaukos iStent
We designed a prospective, non-comparative, uncontrolled, non-randomised, interventional study to assess the efficacy and safety of the Glaukos iStent GTS-400 combined with cataract surgery. The patients enrolled had cataract and primary open-angle glaucoma, pseudoexfoliative glaucoma or OHT.
The tenets of the Declaration of Helsinki and Spanish legislation were adhered to and the study protocol was approved by our institution's Review Board. Before recruitment, written legally binding informed consent for Glaukos iStent implantation and cataract surgery was obtained from each patient.
Subjects were recruited consecutively from the Department of Glaucoma, Hospital Clinico San Carlos (Madrid, Spain). Each subject underwent a comprehensive ophthalmic examination including: review of medical records, Snellen-chart best corrected visual acuity (BCVA), slit lamp biomicroscopy, applanation tonometry (Perkins MK2; Clement Clarke International, Essex, UK), gonioscopy, dilated fundus examination, Pentacam (Oculus, Wetzlar, Germany) examination, ECC (Topcon SP-2000P, Topcon Medical Systems Inc., Japan) and standard automated perimetry (G1-TOP, Octopus 1–2–3, Haag-Streit, USA). Three anterior chamber morphometric measurements were obtained using the Pentacam: anterior chamber depth, anterior chamber volume and anterior chamber angle. ECCs were always conducted by the same examiner, using the clearest image acquired by the retraced method of endothelial cell analysis using the IMAGENET system, as suggested elsewhere.
The inclusion criteria were a previous diagnosis of mild-to-moderate (according to Hodapp classification) open-angle glaucoma (including pseudoexfoliative glaucoma) or OHT, an IOP of 14–30 mm Hg as measured at the last two consecutive visits if receiving ocular hypotensive medications, of 22–30 mm Hg if not or of 22–32 mm Hg after hypotensive drops washout, a concurrent diagnosis of cataract with a preoperative BCVA no better than 0.5, age 18 years or older, and a scleral spur visible on gonioscopy. The patients were also required to understand the information given to provide their consent for the procedure and to express a willingness to attend scheduled follow-up visits for at least 1 year. Subjects were excluded if they had any ocular disease other than primary open-angle glaucoma, pseudoexfoliative glaucoma or OHT, cloudy corneas likely to impair gonioscopic observation of the nasal angle, peripheral anterior synechias, prior eye surgery (including filtering surgery), prior trauma or ocular surface disease, as well as a history of any significant ocular condition that could interfere with the tests. Patients with demonstrated elevated episcleral venous pressure, active thyroid orbitopathy, carotid-cavernous fistula, Sturge-Weber syndrome and orbital tumours or orbital congestive disease were also excluded.
Before surgery, all the patients receiving ocular hypotensive medications were instructed to discontinue their use to obtain baseline IOP measurements (1 week for carbonic anhydrase inhibitors, 2 weeks for α-2 adrenergic agonists and 4 weeks for β-blockers and prostaglandins) No preoperative prophylactic antibiotic treatment was prescribed.
All surgical procedures were performed by two of the authors (JMMC, JG-F). In all patients, standard clear corneal phacoemulsification with the implant of a foldable acrylic IOL was conducted under topical anaesthesia (oxybuprocaine 0.40% plus tetracaine 0.10%, Alcon Cusi, Barcelona, Spain). The surgical technique is similar to that described for the GTS-100 device. After phacoemulsification and IOL placement, two GTS-400 iStents were implanted through the clear corneal incision (~2.85 mm) placed for phacoemulsification. To initiate the iStent implantation procedure, acetylcholine 1% (acetylcholine 1%, Alcon Cusi) was injected into the anterior chamber to constrict the pupil. Next, the anterior chamber was filled with a viscoelastic agent (Healon, Abbott Medical Optics, Santa Ana, California, USA) to improve visualisation of the angle. Due to the nasal localisation of the iStent, the head of the patient must be repositioned at 45° to the opposite side of the eye undergoing surgery, while tilting the microscope 30° for a good view of the trabecular meshwork on the nasal side of the angle using a Swan-Jacob gonioscope. With the iStent on its tip, the inserter was introduced in the anterior chamber and the trabecular meshwork located. The stent was then gently slid through the trabecular meshwork into the Schlemm's canal at the nasal position (3 to 4 o'clock right eye, 9 to 8 o'clock left eye). Once it was ensured that the entire stent is embedded in the trabecular meshwork, it was released from its applicator. The inserter determines the depth of the placement. After checking the stent's position the inserter was withdrawn. The procedure was repeated with a second inserter to insert the second iStent. At the end of the procedure, the anterior chamber is flushed to eliminate any refluxed blood (which is a signal of accurate placement into the Schlemm's canal). This ensures good visualisation to confirm that the implant is well located at sufficient depth. The viscoelastic agent can then be removed and the anterior chamber filled with sufficient saline solution to achieve physiologic pressure.
No topical pressure-lowering medication was administered at the end of the procedure. Postoperative care included antibiotic (tobramycin 0.3%) plus steroid (dexamethasone 0.1%) eye drops (Tobradex, Alcon Cusi) five times a day for 1 week with tapering of the dose for a further 3 weeks. Antiglaucoma topical therapy was introduced postoperatively if the desired target IOP range, as judged by the investigator, was not achieved.
Postoperative visits were scheduled for 1 day, 1 week, 1, 3 and 6 months and 1 year.
Every visit included slit-lamp biomicroscopy, applanation tonometer (Clement Clarke Perkins MK2 Tonometer) IOP measurement, number of glaucoma medications and BCVA. Preoperatively, and 1 month, 3 months and 1 year postoperatively, the nasal angle was examined by gonioscopy. ECCs were obtained preoperatively and 1 month, 6 months and 1 year postoperatively.
The same physician throughout the study, using the same tonometer for IOP measurement, made all the examinations. Calibration of the tonometer was verified at regular basis according to the manufacturer recommendations.
The primary efficacy outcome measure was IOP as measured by Goldmann applanation tonometry. The secondary efficacy outcome measure was the number of antiglaucoma medications used preoperatively and postoperatively. Safety outcome measures were complications, BCVA and ECC. Examinations in the early postoperative period (within 1 month of surgery) consisted mainly of safety assessment.
Kolmogorov–Smirnov test was performed to check normal distribution of the sample. A paired sample t test was used to compare outcomes in the study group. Statistical significance was set at p≤0.05. All statistical tests were performed using SPSS software (SPSS software V.15.0 for Windows; SPSS Inc., Chicago, Illinois, USA).
Methods
Study Design
We designed a prospective, non-comparative, uncontrolled, non-randomised, interventional study to assess the efficacy and safety of the Glaukos iStent GTS-400 combined with cataract surgery. The patients enrolled had cataract and primary open-angle glaucoma, pseudoexfoliative glaucoma or OHT.
The tenets of the Declaration of Helsinki and Spanish legislation were adhered to and the study protocol was approved by our institution's Review Board. Before recruitment, written legally binding informed consent for Glaukos iStent implantation and cataract surgery was obtained from each patient.
Subjects
Subjects were recruited consecutively from the Department of Glaucoma, Hospital Clinico San Carlos (Madrid, Spain). Each subject underwent a comprehensive ophthalmic examination including: review of medical records, Snellen-chart best corrected visual acuity (BCVA), slit lamp biomicroscopy, applanation tonometry (Perkins MK2; Clement Clarke International, Essex, UK), gonioscopy, dilated fundus examination, Pentacam (Oculus, Wetzlar, Germany) examination, ECC (Topcon SP-2000P, Topcon Medical Systems Inc., Japan) and standard automated perimetry (G1-TOP, Octopus 1–2–3, Haag-Streit, USA). Three anterior chamber morphometric measurements were obtained using the Pentacam: anterior chamber depth, anterior chamber volume and anterior chamber angle. ECCs were always conducted by the same examiner, using the clearest image acquired by the retraced method of endothelial cell analysis using the IMAGENET system, as suggested elsewhere.
The inclusion criteria were a previous diagnosis of mild-to-moderate (according to Hodapp classification) open-angle glaucoma (including pseudoexfoliative glaucoma) or OHT, an IOP of 14–30 mm Hg as measured at the last two consecutive visits if receiving ocular hypotensive medications, of 22–30 mm Hg if not or of 22–32 mm Hg after hypotensive drops washout, a concurrent diagnosis of cataract with a preoperative BCVA no better than 0.5, age 18 years or older, and a scleral spur visible on gonioscopy. The patients were also required to understand the information given to provide their consent for the procedure and to express a willingness to attend scheduled follow-up visits for at least 1 year. Subjects were excluded if they had any ocular disease other than primary open-angle glaucoma, pseudoexfoliative glaucoma or OHT, cloudy corneas likely to impair gonioscopic observation of the nasal angle, peripheral anterior synechias, prior eye surgery (including filtering surgery), prior trauma or ocular surface disease, as well as a history of any significant ocular condition that could interfere with the tests. Patients with demonstrated elevated episcleral venous pressure, active thyroid orbitopathy, carotid-cavernous fistula, Sturge-Weber syndrome and orbital tumours or orbital congestive disease were also excluded.
Surgical Technique
Before surgery, all the patients receiving ocular hypotensive medications were instructed to discontinue their use to obtain baseline IOP measurements (1 week for carbonic anhydrase inhibitors, 2 weeks for α-2 adrenergic agonists and 4 weeks for β-blockers and prostaglandins) No preoperative prophylactic antibiotic treatment was prescribed.
All surgical procedures were performed by two of the authors (JMMC, JG-F). In all patients, standard clear corneal phacoemulsification with the implant of a foldable acrylic IOL was conducted under topical anaesthesia (oxybuprocaine 0.40% plus tetracaine 0.10%, Alcon Cusi, Barcelona, Spain). The surgical technique is similar to that described for the GTS-100 device. After phacoemulsification and IOL placement, two GTS-400 iStents were implanted through the clear corneal incision (~2.85 mm) placed for phacoemulsification. To initiate the iStent implantation procedure, acetylcholine 1% (acetylcholine 1%, Alcon Cusi) was injected into the anterior chamber to constrict the pupil. Next, the anterior chamber was filled with a viscoelastic agent (Healon, Abbott Medical Optics, Santa Ana, California, USA) to improve visualisation of the angle. Due to the nasal localisation of the iStent, the head of the patient must be repositioned at 45° to the opposite side of the eye undergoing surgery, while tilting the microscope 30° for a good view of the trabecular meshwork on the nasal side of the angle using a Swan-Jacob gonioscope. With the iStent on its tip, the inserter was introduced in the anterior chamber and the trabecular meshwork located. The stent was then gently slid through the trabecular meshwork into the Schlemm's canal at the nasal position (3 to 4 o'clock right eye, 9 to 8 o'clock left eye). Once it was ensured that the entire stent is embedded in the trabecular meshwork, it was released from its applicator. The inserter determines the depth of the placement. After checking the stent's position the inserter was withdrawn. The procedure was repeated with a second inserter to insert the second iStent. At the end of the procedure, the anterior chamber is flushed to eliminate any refluxed blood (which is a signal of accurate placement into the Schlemm's canal). This ensures good visualisation to confirm that the implant is well located at sufficient depth. The viscoelastic agent can then be removed and the anterior chamber filled with sufficient saline solution to achieve physiologic pressure.
No topical pressure-lowering medication was administered at the end of the procedure. Postoperative care included antibiotic (tobramycin 0.3%) plus steroid (dexamethasone 0.1%) eye drops (Tobradex, Alcon Cusi) five times a day for 1 week with tapering of the dose for a further 3 weeks. Antiglaucoma topical therapy was introduced postoperatively if the desired target IOP range, as judged by the investigator, was not achieved.
Follow-up Examinations
Postoperative visits were scheduled for 1 day, 1 week, 1, 3 and 6 months and 1 year.
Every visit included slit-lamp biomicroscopy, applanation tonometer (Clement Clarke Perkins MK2 Tonometer) IOP measurement, number of glaucoma medications and BCVA. Preoperatively, and 1 month, 3 months and 1 year postoperatively, the nasal angle was examined by gonioscopy. ECCs were obtained preoperatively and 1 month, 6 months and 1 year postoperatively.
The same physician throughout the study, using the same tonometer for IOP measurement, made all the examinations. Calibration of the tonometer was verified at regular basis according to the manufacturer recommendations.
Data Analysis
The primary efficacy outcome measure was IOP as measured by Goldmann applanation tonometry. The secondary efficacy outcome measure was the number of antiglaucoma medications used preoperatively and postoperatively. Safety outcome measures were complications, BCVA and ECC. Examinations in the early postoperative period (within 1 month of surgery) consisted mainly of safety assessment.
Kolmogorov–Smirnov test was performed to check normal distribution of the sample. A paired sample t test was used to compare outcomes in the study group. Statistical significance was set at p≤0.05. All statistical tests were performed using SPSS software (SPSS software V.15.0 for Windows; SPSS Inc., Chicago, Illinois, USA).
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