Comparative In Vitro Flow Study of 3 Different Ex-PRESS Miniature Glaucoma Device Models:

Trabeculectomy with Ologen implant versus trabeculectomy with P 50 Ex-PRESS shunt in primary open-angle glaucoma

Background

This is the first randomized controlled trial of trabeculectomy with Ex-Press Shunt versus Ologen implant in primary open-angle glaucoma (POAG) in Indian eyes.

Methods

A prospective randomized controlled trial of patients of POAG treated with two different methods of augmented trabeculectomy. Group A with Ex-PRESS shunt (P50 model) and Group B with Ologen implant. Surgical success was defined as intraocular pressure of 21 mm Hg or lower at 6 months postoperative.

Results

N = 40 eyes of 33 patients. Baseline IOP in Group A was 23.70 ± 4.6 mm Hg (Range 22-36 mm Hg), and Group B was 26.00 ± 4.0 mm Hg (Range 23-36 mm Hg). Surgical success was achieved in 85% of patients in both Groups. Change in IOP from baseline was statistically significant in both groups at 1, 4, 8, 12 weeks, and 6 months postoperative. No statistically significant difference in the change in IOP between the two groups. Postoperative complications were lesser in Group A compared to Group B, in both early (35% vs 50%) and late stage (20% vs 30%). The drop in visual acuity became statistically insignificant at 4 weeks in Group A and 8 weeks in Group B.

Conclusions

There is no difference between the surgical success rates of trabeculectomy with Ex-PRESS Shunt versus Ologen. However, the Ex-PRESS shunt fares better with lower complication rates and faster visual recovery than the Ologen group.

Evaluation of the Ultrastructural and In Vitro Flow Properties of the PRESERFLO MicroShunt

Purpose

To measure the in vitro flow properties of the PRESERFLO implant for comparison with the theoretical resistance to flow.

Methods

The PRESERFLO was designed to control the flow of aqueous humor according to the Hagen-Poiseuille (HP) equation. Scanning electron microscopy (SEM) was performed to analyze the ultrastructure, and flow measurements were carried out using a gravity-flow setup.

Results

SEM images of the PRESERFLO showed luminal diameters of 67.73 × 65.95 µm and 63.66 × 70.54 µm. The total diameter was 337.2 µm, and the wall was 154 µm wide. The theoretical calculation of the resistance to flow (R) for an aqueous humor (AH) viscosity of 0.7185 centipoises (cP) was 1.3 mm Hg/(µL/min). Hence, assuming a constant AH flow of 2 µL/min, the pressure differential across the device (ΔP) was estimated to be 2.6 mm Hg. The gravity-flow experiment allowed us to measure the experimental resistance to flow, which was R_E = 1.301 mm Hg/(µL/min), in agreement with the theoretical resistance to flow R given by the HP equation.

Conclusions

The experimental and theoretical flow testing showed that the pressure drop across this device would not be large enough to avoid hypotony unless the resistance to outflow of the sub-Tenon space was sufficient to control the intraocular pressure in the early postoperative period.

Translational Relevance

The fluid properties of glaucoma subconjunctival drainage devices determine their specific bleb-forming capacity and ability to avoid hypotony and therefore their safety and efficacy profile.

Computational and experimental analysis of a Glaucoma flat drainage device

This paper presents a computational and experimental analysis of a glaucoma flat drainage device (FDD). The FDD consists of a metallic microplate placed into the eye sclerocorneal limbus, which creates a virtual path between the anterior chamber and its exterior, allowing the intraocular pressure (IOP) to be kept in a normal range. It also uses the surrounding tissue as a flow regulator in order to provide close values of IOP for a wide range of aqueous humor (AH) flow rates. The Neo Hookean hyperelastic model is used for the solid part, while the Reynolds thin film fluid model is used for the fluid part. On the other hand, a gravitational-driven flow test is implemented in order to validate the simulation process. An in vitro experiment evaluated the flow characteristics of the device implanted in fourteen extirpated pig eyes, giving as a result the best-fit for the Young modulus of the tissue surrounding the device. Finally, according to the resulting computational model, for a range of 1.4-3.1 μL/min, the device presents a pressure variation range of 6-7.5 mmHg.

Ex-PRESS shunt implantation for intractable glaucoma with posterior chamber phakic intraocular lens: a case report

Background

Implantation of the posterior chamber phakic intraocular lens has been widely performed to correct high and extreme myopia. Chronic intraocular pressure (IOP) elevation may occur in its late postoperative period. For medically uncontrolled cases, surgical treatment is necessary, and benefits should be weighed against risks when determining whether to remove the lens.

Case presentation

A 32-year-old man with extremely high myopia presented with progressive blurred vision and medically uncontrolled IOP in the right eye. His past ocular history was significant for bilateral implantable collamer lens (ICL) implantation ten years ago. On ophthalmic examination, the ICL was well placed with a vault height of 456 µm in the right eye. The anterior chamber angles were open but narrow, and mild to moderate trabecular pigmentation was noted. Ex-PRESS glaucoma filtration surgery without ICL removal was performed to control IOP. During surgery, an Ex-PRESS P50 shunt was inserted into the anterior chamber via the front edge of the blue-grey transition zone between the sclera and cornea. Transient hypotony and shallow anterior chamber occurred in the first week after surgery, along with an ICL tilt towards the cornea with reduced vault height. No other complications related to either the ICL or the Ex-PRESS shunt were noted. IOP remained stable at 12 ~ 14 mmHg at the first 3-month follow-up.

Conclusions

Ex-PRESS glaucoma filtration surgery might be a safe and effective alternative treatment for intractable glaucoma with high myopia and ICL implantation. Careful assessment of the ICL position and anterior chamber angle is necessary to plan the appropriate surgical procedure. A postoperative shallow anterior chamber may result in ICL dislocation.

Ex-Press P50 device filtering failure due to non-visible intraluminal blockages

PURPOSE

To describe Ex-Press P50 failures due to an internal blockage.

METHODS

A retrospective series of 248 eyes of 219 patients with Ex-Press P50 surgery was conducted. Of these cases, 18 (7.2%) required surgical revision due to filtration failure with no visible blockages in the gonioscopy and no filtering bleb in the slit lamp examination. In all of these cases, we found fibrosis on the edges of the scleral flap. After dissecting the scleral flap, filtration through the implant was restored spontaneously in 10 (4.0%) cases. In two cases fibrous tissue was observed on the tip of the implant and was necessary to remove it. In 6 (2.4%) cases, there was no filtration despite no visible obstruction and attempts to restore the flow were unsuccessful, requiring extraction of the implant and reconverting to trabeculectomy. Two of the removed devices were sanded until the lumen was visible to ascertain the nature of the obstruction.

RESULTS

In our series, the most common cause of failure was episcleral fibrosis. In 2.4% of the cases, the blockage was intraluminal and aqueous flow could not be restored.

CONCLUSION

In the Ex-Press P50 implant an internal blockage, that is not visible through the proximal or distal orifices, may be the cause of failure. Unblocking by surgical maneuvers is not feasible due to the intraluminal design. These cases can be solved by extraction of the implant and conversion to trabeculectomy.

Development of a biodegradable flow resisting polymer membrane for a novel glaucoma microstent

Within this paper we analyzed the technical feasibility of a novel microstent for glaucoma therapy. For lowering of intraocular pressure, the flexible polyurethane (PUR) implant is designed to drain aqueous humour from the anterior chamber of the eye into subconjunctival, or alternatively suprachoroidal, space. The microstent includes a biodegradable, flow resisting polymer membrane serving as temporary flow resistance for the prevention of early postoperative hypotony. A biodegradable local drug delivery (LDD)-device was designed to prevent fibrous encapsulation. Biodegradable components were made of flexible, nonwoven membranes of Poly(4-hydroxybutyrate) (P(4HB)). Polymer samples and microstent prototypes were manufactured by means of dip coating, electrospinning and femtosecond-laser micromachining and characterized in vitro with regard to structural and fluid mechanical properties, degradation behavior and drug release. Bending stiffness of PUR-tubing (62.53 ± 7.57 mN mm²) is comparable to conventional glaucoma drainage devices in a tube-plate design. Microstent prototypes yield a flow resistance of 2.4 ± 0.6 mmHg/μl min^-1 which is close to the aspired value corresponding to physiological pressure (15 mmHg) and aqueous humour flow (2 μl min^-1) conditions inside the eye. Degradation of electrospun P(4HB) specimens was found to be almost completely finished after six months in vitro. Within this time frame, flow capacity of the microstent increases, which is beneficial to compensate potentially increasing flow resistance of fibrous tissue in vivo. Fast drug release of the LDD-device was found. One microstent prototype was implanted into a porcine eye ex vivo. Future preclinical studies will allow further information about Microstent performance.

Ex-PRESS implantation with phacoemulsification in POAG versus CPACG

AIM

To compare the long-term outcomes of the Ex-PRESS miniature glaucoma device implanted under a scleral flap in combination of phacoemulsification with intraocular lens implantation in primary open angle glaucoma (POAG) and chronic primary angle-closure glaucoma (CPACG).

METHODS

Retrospective, comparative study. A total of 60 eyes (60 patients) receiving the Ex-PRESS miniature glaucoma device implantation combined with phacoemulsification were reviewed. Thirty eyes (30 patients) had the combined procedures for POAG, and the other 30 eyes (30 patients) for CPACG.

RESULTS

The follow-up was 39.37±7.09mo (range 3 to 49mo) in patients with POAG and 37.10±9.26mo (range 9 to 49mo) in patients with CPACG (P=0.29). The mean change in best corrected visual acuity was 0.41 logMAR for POAG and 0.38 logMAR for CPACG at the last follow-up (P=0.22). The postoperative intraocular pressure (IOP) of the POAG group was significantly lower than the CPACG group at 1, 3, 12, and 18mo after surgery (P=0.02, 0.00, 0.04, 0.01) with similar glaucoma medications after surgery (P>0.16). At 3y after surgery, the cumulative complete and qualified success rates were 63.3% (POAG) and 53.3% (CPACG), 83.3% (POAG) and 73.3% (CPACG) (P=0.41, 0.49), respectively. The POAG group had more hypotony than the CPACG group (P=0.04).

CONCLUSION

The long-term outcomes show the Ex-PRESS implantation combined with phacoemulcification can effectively lower the IOP in both the POAG and CPACG groups. The POAG group seems to have lower postoperative IOP and a higher risk of hypotony.

Evaluation of the Ex-PRESS(®) P-50 implant under scleral flap in combined cataract and glaucoma surgery

AIM

To evaluate the efficacy and safety of glaucoma drainage device Ex-PRESS(®) P-50 for combined cataract surgery and glaucoma.

METHODS

Patients having cataract and open angle glaucoma or patients with open advanced glaucoma which needed two or more antiglaucoma medications were included. Combined cataract surgery and glaucoma with Ex-PRESS(®) P-50 model placed under scleral flap was performed.

RESULTS

Out of 40 eyes of 40 patients (55% male and 45% female) completed the study during one-year follow-up. The mean of age was 76.6±11.02y. The intraocular pressure (IOP) decreased significantly during the 12-month follow-up from 23.5 mm Hg to 16.8 mm Hg (Wilcoxon signed ranks test, P<0.001). A 59.5% of patients did not need any topical treatment, 10.8% of them needed one active principle, 27% needed two active principles, and 2.7% of them needed three active principles for successful IOP control (<21 mm Hg).

CONCLUSION

Combined surgery of phacoemulsification with ExPRESS(®) P-50 lowers IOP from the preoperative baseline and reduces significantly the number of antiglaucoma active principles for IOP control after the operation.

Evaluation of Dimensional and Flow Properties of ExPress Glaucoma Drainage Devices

PURPOSE

ExPress devices are available as P50 and P200 models, the numbers related to their luminal diameters in μm. We compared their Poiseuille's Law-based theoretical resistance values with experimental values and correlated these with their luminal dimensions derived from electron microscopy.

METHODS

Scanning electron microscopy was performed on P50 and P200 devices. Bench-top flow studies were performed to find the resistances of the devices. Devices were also incorporated into a perfused, ex vivo porcine sclera model to test and compare their control of pressure, with and without overlying scleral flaps, and with trabeculectomies.

RESULTS

The luminal dimensions of the P200 device were 206.4±3.3 and 204.5±0.9 μm at the subconjunctival space and anterior chamber ends, respectively. Those of the P50 device were 205.0±5.8 and 206.9±3.7 μm, respectively. There were no significant differences between the P200 and P50 devices (all P>0.05). The resistances of the P200 and P50 devices were 0.010±0.001 and 0.054±0.002 mm Hg/μL/min, respectively (P<0.05). Equilibrium pressures with overlying scleral flaps were 17.81±3.30 mm Hg for the P50, 17.31±4.24 mm Hg for the P200, and 16.28±6.67 mm Hg for trabeculectomies (P=0.850).

CONCLUSIONS

The luminal diameters of both devices are externally similar. The effective luminal diameter of the P50 is much larger than 50 μm. Both devices have low resistance values, making them unlikely to prevent hypotony on their own. They lead to similar equilibrium pressures as the trabeculectomy procedure when inserted under the scleral flap.

Meta-analysis of randomized controlled trials comparing EX-PRESS implantation with trabeculectomy for open-angle glaucoma

Purpose

To evaluate the efficacy and safety of EX-PRESS implantation compared with trabeculectomy for uncontrolled open-angle glaucoma.

Methods

Pertinent randomized controlled trials were identified through systematic searches of the PubMed, EMBASE, and Cochrane Library. The efficacy measures utilized were the weighted mean differences (WMDs) for the intraocular pressure reduction (IOPR), the reduction in glaucoma medications, the change of visual acuity, and the relative risks (RRs) for operative success rates. The safety measures utilized were RRs for postoperative complications. The pooled effects were calculated using the random-effects model.

Results

Four randomized controlled trials of 292 eyes were included in this meta-analysis. The WMDs of the IOPR comparing the EX-PRESS with trabeculectomy were −0.25 (95% Cl: −3.61 to 3.11) at 6 month, 0.053 (−4.31 to 4.42) at 12 months, 0.81 (−4.06 to 5.67) at 24 months, and 0.20 (−2.11 to 2.51) at final follow-up. There was no statistically significance for IOPR at any point after surgery. There were also no significant differences in the reduction in glaucoma medications or visual acuity between the groups. The pooled relative risks comparing EX-PRESS with Trabeculectomy were 1.36 (1.11 to 1.66) for the complete operative success rate and 1.05 (0.94 to 1.17) for the qualified operative success rate. EX-PRESS and Trabeculectomy were associated with similar incidences in most complications with the exception of hyphema, with pooled RR being 0.18 (0.046 to 0.66).

Conclusions

EX-PRESS implantation and trabeculectomy have similar efficacy in IOP-lowering, medication reduction, vision recovery, and qualified operative success rates. EX-PRESS associated with higher rates of complete operative success and fewer hyphema than with Trabeculectomy. However, these should be interpreted with caution because of the inherent limitations of the included studies.