Viscocanalostomy in rhesus monkeys

Alternative application of an iTrack microcatheter and canaloplasty: case report and literature review

INTRODUCTION

Glaucoma is the leading cause of irreversible blindness worldwide. Schlemm's canal surgery using an iTrack flexible microcatheter has become popular because of its high quality-of-life issues and the growing demand for less invasive but effective procedures. The unique design of the microcatheter makes it a multimodal tool, which can be used not only in the field of antiglaucoma surgery but also as a drug delivery system to treat various conditions.

AREAS COVERED

This review presents an update on the selected aspects of a drug delivery system using the iTrack microcatheter, including glaucoma gene therapy and posterior-segment diseases, both in animal models and human patients. The authors also report the case of a patient with branch retinal vein occlusion treated with suprachoroidal bevacizumab in the submacular region administered with the iTrack catheter.

EXPERT OPINION

The findings presented in this study may indicate that the application of a microcatheter in open-angle glaucoma gene therapy is reasonable and can be combined with full or partial surgical canaloplasty procedures. Translation of this potential into a treatment modality would require overcoming multiple barriers.

Combined phacoviscocanalostomy versus phacoemulsification alone in patients with coexisting cataract and mild-to-moderate open-angle glaucoma; a randomized-controlled trial

BACKGROUND/OBJECTIVE

Management of concomitant cataract and glaucoma depends on the stage of glaucoma and the patient's situation. There are different surgical options for handling visually significant cataract and mild-to-moderate open-angle glaucoma (OAG). We aimed to compare the one-year results of phacoemulsification alone versus phacoviscocanalostomy in these patients.

SUBJECTS/METHODS

This was a parallel-arm, single-masked, randomized-controlled trial, conducted at Farabi Eye Hospital, Tehran, Iran between January 2016 and January 2018. We enrolled 89 eyes from 89 patients with mild-to-moderate primary OAG or pseudoexfoliative glaucoma (PEXG) with visually significant age-related cataract. They randomly underwent phacoemulsification alone (n = 44) or combined phaco-viscocanalostomy (n = 45). All patients had a 12-month follow-up period, and the mean intraocular pressure (IOP), the number of antiglaucoma medications, and complete and qualified success rates were compared.

RESULTS

After the 1st and 3rd months, the mean IOP showed significantly decreased in the phaco-visco group compared to the phaco group (P < 0001 and P = 0.004, respectively), but it was not statistically significant at 6th and 12th months (P = 0.540 and P = 0.530). The need for antiglaucoma medication and the complete and qualified success rates were significantly in favour of the phaco-visco group in all postoperative visits (P < 0.05).

CONCLUSIONS

Although both phacoemulsification alone and phacoviscocanalostomy procedures can be considered for patients with mild-to-moderate OAG, we found better success rates using phacoviscocanalostomy. Therefore, if the surgeon is an expert in performing this technique, this non-penetrating procedure can be applied in patients with visually significant cataract and earlier stages of OAG, especially in patients with PEXG.

Modified Viscotrabeculotomy with Microcatheter: Our Technique and Experience in the Surgical management of Glaucoma

Aims

To present the results of our case series with a technique we defined as “modified viscotrabeculotomy” which incorporates the benefits of 360° of trabeculotomy and viscodilation and viscodissection of canal of Schlemm using a microcatheter.

Materials and methods

This study was designed as a prospective interventional case series and was conducted in Cerrahpasa Medical School Ophthalmology Clinic. Forty-one eyes of 30 patients diagnosed with congenital glaucoma (CG) underwent modified viscotrabeculotomy surgery following initial preoperative examination. The main outcome measure was the surgical success of the procedure, which is determined by an intraocular pressure (IOP) of <18 mm Hg without medication or resurgery; qualified success is defined as an IOP of <18 mm Hg under general anesthesia with an additional need for medications. The differences in IOP measurements were analyzed using paired analysis of variance (ANOVA) with repeated measures.

Results

The mean preoperative IOP of the patients was 32.27 ± 4.89 mm Hg. The IOP values at the 1st, 3rd, 6th postoperative months, and at the last visit were 13.41 ± 2.25 mm Hg, 13.70 ± 1.78 mm Hg, 12.47 ± 1.57 mm Hg, and 12.26 ± 1.81 mm Hg, respectively. The difference between the preoperative IOP values and postoperative IOP values was statistically significant (p < 0.001). The qualified surgical success rate was 94.4% after a mean follow-up of 27.95 ± 8.25 months (range 15–45 months).

Conclusion

Modified viscotrabeculotomy is a safe and effective treatment in the management of CG.

How to cite this article

Tamçelik N, Capar O, Atalay E. Modified Viscotrabeculotomy with Microcatheter: Our Technique and Experience in the Surgical management of Glaucoma. J Curr Glaucoma Pract 2019;13(3):88–93.

Thrombospondin-2 is up-regulated by TGFβ2 and increases fibronectin expression in human trabecular meshwork cells

Elevated intraocular pressure (IOP) is a major risk factor for the development of primary open-angle glaucoma (POAG). This is from an increased aqueous humour (AH) outflow resistance through the trabecular meshwork (TM). The pathogenic mechanisms leading to the increase in TM outflow resistance are poorly understood but are thought to be from a dysregulation of the TM extracellular matrix (ECM) environment. ECM modification and turnover are crucial in regulating the resistance to aqueous outflow. ECM turnover is influenced by a complex interplay of growth factors such as transforming growth factors (TGFβ) family and matrix metalloproteinases (MMPs). Elevated TGFβ2 levels result in an increase in ECM deposition such as fibronectin leading to increased resistance. Fibronectin is a major component of TM ECM and plays a key role in its maintenance. Thrombospondins (TSP)-1 and -2 are important regulators of the ECM environment. TSP-1 has been implicated in the pathogenesis of POAG through activation of TGFβ2 within the TM. TSP-2 does not contain the catalytic domain to activate latent TGFβ, but is able to mediate the activities of MMP 2 and 9, thereby influencing ECM turnover. TSP-2 knock out mice show lower IOP levels compared to their wild type counterparts, suggesting the involvement of TSP-2 in the pathogenesis of POAG but its role in the pathogenesis of POAG remains unclear. The purpose of this study was to investigate the role of TSP-2 in trabecular meshwork ECM regulation and hence the pathogenesis of POAG. TSP-1 and TSP-2 expressions in immortalised glaucomatous TM cells (GTM3) and primary human non-glaucomatous (NTM) and glaucomatous cells (GTM) were determined by immunocytochemistry, immuno-blot analysis and qPCR following treatment with TGFβ2 and Dexamethasone. The level of ECM protein fibronectin was determined in TM cells using immuno-blot analysis following treatment with TSP-1 or -2. TM cells secrete TSP-1 and -2 under basal conditions at the protein level and TSP-2 mRNA and protein levels were increased in response to TGFβ2 three days post treatment. Exogenous treatment with TSP-2 up-regulated the expression of fibronectin protein in GTM3 cells, primary NTM and GTM cells. TSP-1 did not affect fibronectin protein levels in GTM3 cells. This suggests that the role of TSP-2 might be distinct from that of TSP-1 in the regulation of the TM cell ECM environment. TSP-2 may be involved in the pathogenesis of POAG and contribute to increased IOP levels by increasing the deposition of fibronectin within the ECM in response to TGFβ2.

Long-term results of up to 12 years of over 700 cases of viscocanalostomy for open-angle glaucoma

PURPOSE

To study the safety and long-term efficacy of classic viscocanalostomy in patients with open-angle glaucoma (OAG) in different populations.

METHODS

A total of 726 eyes of 726 patients from Europe or South Africa with primary OAG (POAG) and pseudoexfoliative glaucoma (PXFG) were included in this retrospective multicentre study. Complete (qualified) success was defined as an intraocular pressure (IOP) equal to or lower than 21, 18 and 16 mmHg without (with or without) medications, respectively. A failed procedure was defined if IOP was above 21 mmHg, not controllable by laser goniopuncture or medications.

RESULTS

The mean IOP before surgery was 42.6 ± 14.2 mmHg for all patients, 29.6 ± 6.6 mmHg for European patients and 48.1 ± 12.9 mmHg for African patients. The follow-up time was 86.2 ± 43.1 months. Mean IOP was 15.4 ± 3.6 mmHg at 5 years, 15.5 ± 4.4 mmHg at 10 years and 16.8 ± 4.2 mmHg at 15 years. The qualified success rate for an IOP of 21, 18 or 16 mmHg or less after 5 years was 92% [95% confidence interval (CI) 0.88-0.96], 70% (95% CI 0.63-0.77) and 43% (95% CI 0.36-0.51) in European patients, and 90% (95% CI 0.87-0.93), 77% (95% CI 0.74-0.81) and 67% (95% CI 0.63-0.72) in African patients, respectively. There was no difference between the success rate for POAG and PXFG for an IOP of 21, 18 or 16 mmHg or less at 5 years (p = 0.64, p = 0.20, p = 0.22, respectively). Laser goniopuncture was performed postoperatively on a total of 127 eyes (17.7%), lowering the pressure from 23.1 ± 1.9 mmHg to 15.0 ± 2.2 mmHg. There were no significant complications, in particular, no blebitis or endophthalmitis.

CONCLUSION

Viscocanalostomy produced a sustained long-term reduction of IOP with a low-risk profile in European and African patients with OAG over 12 years.

Surgery on the Trabecular Meshwork: Histopathological Evidence

Juxtacanalicular (JXT) trabecular meshwork and endothelial lining of Schlemm's canal have been cited as the loci of aqueous outflow resistance, both in a normal as well as a glaucomatous eye. In this review, we attempt to understand the currently available surgical modalities in light of the available histopathological evidence, regarding localization of outflow resistance. How to cite this article: Bhartiya S, Ichhpujani P, Shaarawy T. Surgery on the Trabecular Meshwork: Histopathological Evidence. J Curr Glaucoma Pract 2015;9(2):51-61.

Deep sclerectomy with bevacizumab and mitomycin C: a comparative study

PURPOSE

To assess the comparative efficacy and safety of primary deep sclerectomy (DS) augmented with subconjunctival Bevacizumab and intraoperative Mitomycin C (MMC).

METHODS

Retrospective, comparative case-control series of consecutive primary DS between January 2008 and December 2010. Seventy-five eyes of 73 patients were included, with 32 eyes in the MMC and 43 in the Bevacizumab group. MMC (0.2 mg/mL for 2 min) was applied subconjunctivally before scleral flap dissection. Bevacizumab (2.5 mg in 0.1 mL) was injected subconjunctivally at the end of surgery. Complete success was intraocular pressure (IOP) <19 mm Hg and a 20% decrease from baseline with no postoperative medications.

RESULTS

There were no significant baseline differences between the groups. Follow-up after DS was 33.3 ± 6.1 months for the Bevacizumab and 35.0 ± 10.2 months for the MMC group (P=0.34). Complete success rates were 90.7% [95% confidence interval (CI), 82.4%-99.8%] and 87.5% (95% CI, 76.8%-99.7%) at 1 year and 76.5% (95% CI, 64.8%-90.4%) and 74.4% (95% CI, 60.5%-91.4%) at 2 years after DS in the Bevacizumab and MMC groups, respectively (P=0.52). There was no statistical difference in mean IOPs between the groups at all specified time intervals up to 2 years (P=0.28). At last follow-up 2 (6.2%) of the MMC and 2 (4.7%) eyes of Bevacizumab group were on medications to control IOP. Eighteen eyes had complications, 9 (20.9%) in Bevacizumab and 9 (28.1%) in the MMC group (P=0.8).

CONCLUSION

Subconjunctival Bevacizumab with primary DS appears to be as efficacious as MMC augmentation with no additional side effects.

Identification of adult stem cells in Schwalbe's line region of the primate eye

PURPOSE

To identify stem cells in the chamber angle of the monkey eye by detection of 5-bromo-2'-deoxyuridine (BrdU) long-term retention.

METHODS

Four cynomolgus monkeys were treated with BrdU via subcutaneous pumps for 4 weeks. The eyes of two animals were processed immediately thereafter (group 1) while in the other animals, BrdU treatment was discontinued for 4 weeks to allow identification of cells with long-term BrdU retention (group 2). The number of BrdU-positive nuclei was quantified, and the cells were characterized by immunohistochemistry and transmission electron microscopy (TEM).

RESULTS

The number of BrdU-positive cells was higher at Schwalbe's line covering the peripheral end of Descemet's membrane than in Schlemm's canal (SC) endothelium, trabecular meshwork (TM), and scleral spur (SS). Labeling with BrdU in SC, TM, and SS was less intense and the number of labeled cells was smaller in group 2 than in group 1. In contrast, in cells of Schwalbe's line the intensity of BrdU staining and the number of BrdU-positive cells was similar when group 1 and 2 monkeys were compared with each other, indicating long-term BrdU retention. Cells that were BrdU-positive in Schwalbe's line region stained for the stem cell marker OCT4. Details of a stem cell niche in Schwalbe's line region were identified by TEM.

CONCLUSIONS

We provide evidence for a niche in the Schwalbe's line region harboring cells with long-term BrdU retention and OCT4 immunoreactivity. The cells likely constitute a population of adult stem cells with the capability to compensate for the loss of TM and/or corneal endothelial cells.

Application of canaloplasty in glaucoma gene therapy: where are we?

PURPOSE

Schlemm's canal (SC) inner wall is adjacent to the juxtacanalicular trabecular meshwork (TM) over their entire circumference. We seek to transfer reporter and therapeutic genes to these outflow-modulating tissues via canaloplasty surgery in live monkeys.

METHODS

A standard canaloplasty surgical approach was performed in cynomolgus monkeys using flexible canaloplasty catheters, modified for monkey eyes with a 175-μm outer diameter and an LED-lighted tip. A 6-0 prolene suture was used for the exact localization of SC. Trypan blue was injected during catheter withdrawal to document catheter placement within SC and to determine ease of injecting fluid into SC. Before, during, and after the injection, the position of the catheter and the anatomic details were video-captured with an externally positioned noncontact endoscopic imaging system and 50 mHz ultrasound biomicroscopy (UBM).

RESULTS

A 360° catheterization and injection of dye into SC was achieved. Suture, catheter, and trypan blue were imaged with the endoscope camera system and the catheter was also visualized with UBM. Trypan blue was seen in the SC over 5 clock hours after a 1 clock-hour insertion of the catheter.

CONCLUSIONS

A modified canaloplasty catheter device might be used for gene delivery to the SC/TM area without circumferential catheterization. Further studies comparing different delivery methods of the vector/transgene into the SC using canaloplasty are needed.

A Potential Application of Canaloplasty in Glaucoma Gene Therapy

Canaloplasty, a recently developed non-penetrating glaucoma surgical approach, may restore physiological outflow routes in primary open-angle glaucoma with less risk of severe postoperative complications than trabeculectomy. Since the inner wall of Schlemm's canal (SC) is directly in contact with the trabecular meshwork (TM) for 360 degrees and the catheter device used in canaloplasty allows viscoelastic to be injected into the entire length of SC, canaloplasty might also be used to perform SC/TM-targeted delivery of transgene vectors for glaucoma gene therapy. This hypothesized new method for transgene delivery may give the transgene access to the entire inner wall of SC and the whole juxtacanalicular region of the TM and allow the transgene to be expressed in both the TM and SC without affecting the cornea, iris and ciliary body. Further, this strategy might have a greater trabecular outflow resistance-decreasing effect than either the genetic or surgical approach alone.

Clinical options for the reduction of elevated intraocular pressure

Elevated IOP in clinical practice is usually seen in glaucoma or ocular hypertension. Glaucoma affects 60 million people worldwide and 8.4 million are bilaterally blind from this chronic disease.1 Options for reducing IOP rely on pharmacological agents, laser treatments and surgery which may be penetrating or non-penetrating. The last twenty years has seen significant changes in all of these strategies. This review aims to cover these clinical options and introduce some of the new technologies currently in development for the clinical lowering of IOP.

Use of viscoelastic substance in ophthalmic surgery - focus on sodium hyaluronate

Among viscoelastic substances, sodium hyaluronate has become the most popular for intraocular surgeries since the introduction of Healon^® (sodium hyaluronate 1%, 4 × 10⁶ daltons) in 1979. This review focuses on the recent development of a new generation of sodium hyaluronate agents with new rheologic properties and the relevant new techniques used in cataract, glaucoma, corneal, and vitreoretinal surgeries. The introduction of sodium hyaluronate agents with different rheologic properties has improved the safety and reliability of intraocular surgeries. Although there have been numerous studies reporting the effectiveness of viscoelastic substances in intraocular surgeries, rigorous validation by multi-center randomized control trials is lacking in many cases. At present, no single viscoelastic agent is most suitable to all of the various intraocular surgical techniques. Therefore, ophthalmologic surgeons should keep up with recent developments of viscoelastic agents and relevant surgical techniques for better patient care.

Modified deep sclerectomy (D-lectomy MMC) for primary open-angle glaucoma: preliminary results

PURPOSE

To evaluate the outcome of modified deep sclerectomy [D-lectomy mitomycin C (MMC)] for medically refractory glaucoma patients.

METHODS

In a retrospective comparative study, the surgical outcome in 1 eye each of 31 patients who underwent D-lectomy MMC was compared with that of 91 eyes of 91 patients who underwent trabeculectomy with adjunctive MMC. These eyes had a diagnosis of primary open-angle glaucoma or pseudoexfoliation glaucoma, a record of high intraocular pressure (IOP) exceeding 25 mm Hg, and planned for surgical intervention. In the D-lectomy MMC cases, a slit incision at the trabecular meshwork and peripheral iridectomy were created. The "lake" and trabeculo-Descemet membrane ("window") were examined by ultrasound biomicroscope, gonioscopy, and time-domain optical coherence tomography.

RESULTS

Postsurgical IOP at 1, 3, 6, and 12 months after the D-lectomy MMC and trabeculectomy MMC were comparable (P=0.63-0.97). The filtering bleb was noted in 14 (45%) of the 31 D-lectomy MMC eyes at 3 months, and their survival was significantly less than trabeculectomy MMC subjects in which 81 of 91 eyes had the bleb at 3 months (P<0.0001). The lake was noted in 29 of 31 D-lectomy MMC eyes. The sealing of the once penetrated trabecular meshwork was complete at 3 months in 23 of 29 eyes by ultrasound biomicroscopic and/or gonioscopic examinations, whereas that was incomplete in 6 eyes.

CONCLUSIONS

Addition of a slit incision to the trabecular meshwork and peripheral iridectomy (D-lectomy MMC) improved postsurgical IOP of the deep sclerectomy to the level comparable with trabeculectomy MMC, with a less frequency of the bleb formation.

Nonpenetrating glaucoma surgery

Nonpenetrating glaucoma surgeries have been developed in recent years in order to improve the safety of conventional filtering procedures. The goal of nonpenetrating filtering procedures is to reduce intraocular pressure by enhancing the natural aqueous outflow channels, while reducing outflow resistance located in the inner wall of the Schlemm's canal and the juxtacanalicular trabecular meshwork. In the last few years viscocanalostomy and deep sclerectomy with external trabeculectomy have become the most popular nonpenetrating filtering procedures. Both involve removal of a deep scleral flap, the external wall of Schlemm's canal and corneal stroma behind the anterior trabeculum and Descemet's membrane, thus creating an intrascleral space. The aqueous humour leaves the anterior chamber through the intact trabeculo-Descemet's membrane into the scleral space, from where it will egress into different pathways. The technique is associated with a long learning curve. Published clinical trials comparing nonpenetrating glaucoma surgery to full-thickness trabeculectomy have a consensus on the superior safety profile of nonpenetrating glaucoma surgery but are not in agreement when it comes to efficacy, where conflicting results have been found. This article reviews the nonpenetrating surgical techniques, mechanisms of action, indications, contraindications, complications, and results.

Combined viscocanalostomy-trabeculectomy for management of far-advanced glaucoma: evaluation of the early postoperative course

BACKGROUND AND OBJECTIVE

To study the early postoperative efficacy and safety of combined viscocanalostomy with trabeculectomy (VISCO-TRAB) for treating far-advanced glaucoma.

PATIENTS AND METHODS

Patients with far-advanced glaucoma scheduled for glaucoma surgery were enrolled in the study. Surgery included viscocanalostomy until Schlemm's canal was deroofed and dilated with viscoelastic, followed by penetrating corneotrabeculectomy, peripheral iridectomy, and tight closure of lamellar flap. Patients with severe glaucoma who were treated with trabeculectomy only (TRAB) in the preceding year were used for comparison.

RESULTS

The study included 39 eyes in the VISCO-TRAB group and 40 eyes in the TRAB group. Mean intraocular pressure was significantly lower in the VISCO-TRAB group during the early postoperative period (P < .05). The postoperative course was less eventful in the VISCO-TRAB group with minimal hypotony or suture lysis-related complications.

CONCLUSION

During the early postoperative period, VISCO-TRAB proved efficacious and safe in reducing intraocular pressure to target levels in patients with far-advanced glaucoma.

Phaco-viscocanalostomy versus Phaco-trabeculotomy

PURPOSE

To compare the surgical outcomes between phaco-viscocanalostomy and phaco-trabeculotomy in open-angle glaucoma.

PATIENTS AND METHODS

In a nonrandomized, retrospective clinical study, 110 eyes underwent phaco-viscocanalostomy (VCS group), and 110 eyes underwent phaco-trabeculotomy (LOT group). The mean follow-up was 857+/-409 (+/-SD) days (P=0.4777).

RESULTS

The mean preoperative treated intraocular pressure (IOP) values were 20.2+/-3.5 mm Hg in the VCS group and 20.9+/-3.5 mm Hg in the LOT group (P=0.3377). The postoperative IOPs in the VCS group were 15.0+/-3.0 and 16.1+/-3.0 mm Hg at 1 and 3 years, and in the LOT group 16.3+/-2.9 mm Hg (P=0.0088) and 16.5+/-3.3 mm Hg (P=0.4993), respectively. The number of medications used in the VCS group was significantly lower than in the LOT group during the observation periods (P< or =0.0130). The probabilities of achieving IOPs< or =21 mm Hg at 3 years in the VCS group were 92.0% with or without mediations and 58.2% without medications, and were significantly better than those of the LOT group (84.7% and 36.0%, P=0.0334 and P<0.0001 by log-rank test, respectively). The probabilities of achieving IOPs< or =16 mm Hg at 3 years in the VCS group were 30.5% with or without mediations and 30.3% without medications, whereas those in the LOT group were 27.5% (P=0.1799) and 19.4% (P=0.0010), respectively. The visual outcome was similar between the groups. Postoperative hyphema (> or =2 mm) and IOP spikes (> or =30 mm Hg) occurred significantly less in the VCS group (2.7 and 3.6%, respectively) than in the LOT group (26.4 and 28.2%, respectively; P<0.0001). In 13 eyes (11.8%) of the LOT group, the highest IOP level was recorded 40 mm Hg or higher. Vitreous hemorrhage and central visual loss occurred in 1 case each in the LOT group.

CONCLUSIONS

After a middle-term observation, phaco-viscocanalostomy provides better IOP control and a lower incidence of vision-threatening complications than phaco-trabeculotomy.

Primary viscocanalostomy for juvenile open-angle glaucoma

PURPOSE

To evaluate the efficacy and safety of primary viscocanalostomy for medically uncontrolled juvenile open-angle glaucoma (JOAG).

DESIGN

Prospective, noncomparative, interventional case-series study.

METHODS

The study included 20 eyes of 20 consecutive patients with medically uncontrolled JOAG who were treated by viscocanalostomy at one institution. No surgical or laser procedure preceded viscocanalostomy. Surgical outcome was defined as an overall success by the following criteria: no visual field deterioration, no optic-neuropathy progression, postoperative intraocular pressure IOP < or =20 mm Hg, and IOP reduction > or =30% compared with baseline values with or without medication. When medications were not required, success was defined as complete. Cases that did not fulfill the aforementioned criteria and cases in which a surgical revision or further goniopuncture was performed were defined as a failure.

RESULTS

Gender distribution was similar. Fourteen eyes belonged to the white race; five eyes belonged to the black race, and one eye belonged to Arab ethnicity. Mean age (+/-SD) at operation was 33.77 +/- 6.16 years, with the mean preoperative IOP (+/-SD) at 22.9 +/- 4.77 mm Hg. Thirty-six months after operation, 16 cases (80%) were considered an overall success. In 11 cases (55%), success was complete. Four cases (20%) were considered failures. No serious complications were documented either during or after operation. In two cases (10%), we documented a spontaneously reabsorbed microhyphema. Trabeculo-Descemet-membrane microperforation occurred in two cases (10%). In two other cases (10%), Trabeculo-Descemet-membrane perforation occurred and was accompanied by iris prolapse that needed peripheral iridectomy.

CONCLUSION

Primary viscocanalostomy can efficiently and safely reduce intraocular pressure in cases of medically uncontrolled JOAG and provide a rational alternative to conventional surgical modalities.