Determinants of Bleb Morphology in Minimally Invasive, Clear-Cornea Micropenetrating Glaucoma Surgery with Mitomycin C

Development and Verification of a Novel Three-Dimensional Aqueous Outflow Model for High-Throughput Drug Screening

Distal outflow bleb-forming procedures in ophthalmic surgery expose subconjunctival tissue to inflammatory cytokines present in the aqueous humor, resulting in impaired outflow and, consequently, increased intraocular pressure. Clinically, this manifests as an increased risk of surgical failure often necessitating revision. This study (1) introduces a novel high-throughput screening platform for testing potential anti-fibrotic compounds and (2) assesses the clinical viability of modulating the transforming growth factor beta-SMAD2/3 pathway as a key contributor to post-operative outflow reduction, using the signal transduction inhibitor verteporfin. Human Tenon's capsule fibroblasts (HTCFs) were cultured within a 3D collagen matrix in a microfluidic system modelling aqueous humor drainage. The perfusate was augmented with transforming growth factor beta 1 (TGFβ1), and afferent pressure to the tissue-mimetic was continuously monitored to detect treatment-related pressure elevations. Co-treatment with verteporfin was employed to evaluate its capacity to counteract TGFβ1 induced pressure changes. Immunofluorescent studies were conducted on the tissue-mimetic to corroborate the pressure data with cellular changes. Introduction of TGFβ1 induced treatment-related afferent pressure increase in the tissue-mimetic. HTCFs treated with TGFβ1 displayed visibly enlarged cytoskeletons and stress fiber formation, consistent with myofibroblast transformation. Importantly, verteporfin effectively mitigated these changes, reducing both afferent pressure increases and cytoskeletal alterations. In summary, this study models the pathological filtration bleb response to TGFβ1, while demonstrating verteporfin's effectiveness in ameliorating both functional and cellular changes caused by TGFβ1. These demonstrate modulation of the aforementioned pathway as a potential avenue for addressing post-operative changes and reductions in filtration bleb outflow capacity. Furthermore, the establishment of a high-throughput screening platform offers a valuable pre-animal testing tool for investigating potential compounds to facilitate surgical wound healing.

Effect of Two Novel Sustained-Release Drug Delivery Systems on Bleb Fibrosis: An In Vivo Glaucoma Drainage Device Study in a Rabbit Model

PURPOSE

To evaluate two drug delivery systems, a nonbiodegradable poly(2-hydroxyethyl methacrylate) (P[HEMA]) system with mitomycin C (MMC) and a biodegradable poly(lactic-co-glycolic acid) (PLGA) system with 5-fluorouracil (5-FU) with and without MMC for their ability to reduce fibrosis when attached to an Ahmed glaucoma valve (AGV) and implanted in a rabbit model.

METHODS

New Zealand albino rabbits (48) were divided into six equal groups, and AGVs, modified as described below, were implanted in the right eye of each rabbit. The groups included (1) PLGA alone; (2) P(HEMA) plus MMC (6.5 μg); (3) PLGA plus 5-FU (0.45 mg); (4) PLGA plus 5-FU (1.35 mg); (5) PLGA plus 5-FU and MMC (0.45 mg and 0.65 μg, respectively); (6) PLGA plus 5-FU and MMC (1.35 mg and 0.65 μg, respectively). The rabbits were followed for 3 months prior to euthanasia.

RESULTS

The bleb wall thickness was significantly less in groups 2, 5, and 6 compared to the rest. At 3 months, the PLGA polymer had completely disappeared, while the P(HEMA) polymer remained intact. There were no statistical differences in the degree of clinically graded conjunctival injection, histologic inflammation, or histologic fibrosis among the six groups.

CONCLUSIONS

We successfully created a sustained-release drug delivery system that decreased the postoperative fibrosis using both a nonbiodegradable P(HEMA) polymer and a biodegradable (PLGA) polymer. Both systems appear to work equally well with no side effects.

TRANSLATIONAL RELEVANCE

These results are supportive of the antifibrotic effect of the slow-release drug delivery system following glaucoma drainage device implantation, thus paving the way for human pilot studies.

Needle bleb revision with bevacizumab and mitomycin C compared with mitomycin C alone for failing filtration blebs

PURPOSE

To report the 6-month comparative outcomes and bleb morphology for needle revision with bevacizumab and mitomycin C (MMC) versus MMC alone of failed trabeculectomy and ExPRESS shunt blebs.

METHODS

Patients undergoing bleb needle revision procedures were enrolled in this study. All patients received a subconjunctival injection of 0.1 mL MMC (0.4 mg/mL) mixed with 0.1 mL preservative-free lidocaine (1%) at the beginning of the procedure. The patients were randomized into 2 cohorts assigned to receive either 1.0 mg (0.04 mL of 25 mg/mL) subconjunctival bevacizumab (treatment group) or 0.04 mL of balanced salt solution (control group) injected in an identical manner posterior to the bleb after the bleb needling. Success was defined as ≥20% reduction in intraocular pressure (IOP) without any IOP-lowering medications. Qualified success was defined as ≥20% reduction of IOP with IOP-lowering medications. Failure was defined as IOP>21 mm Hg, IOP reduction <20%, or need for additional surgery. Bleb morphology was classified using the Indiana Bleb Appearance Grading Scale.

RESULTS

Six months postoperatively, in treatment group (n=29), 57% of patients achieved complete success, and 43% failed. In control group (n=29), 41% of patients achieved complete success, 7% achieved qualified success, and 52% failed. The difference in success rates between the 2 groups was not statistically significant (P=0.35). At 6 months, the mean IOP was 11.52 in treatment group and 12.83 in control group (P=0.45); patients in treatment group were on a mean of 0.16 medications as compared with 0.58 medications in control group (P=0.058). For bleb morphology of treatment group compared with control group, the blebs had less vascularity (0.76 vs. 1.20, respectively, on a scale of 0 to 4, P<0.05) and greater extent (2.68 vs. 2.36, on a scale of 0 to 3, P=0.022) in treatment group.

CONCLUSIONS

There was no significant difference between the success rates and IOPs at postoperative month 6 between treatment and control groups. Postoperative blebs in the treatment group were less vascular and had greater extent.

Long-term outcomes of needle revision of trabeculectomy blebs with mitomycin C and 5-fluorouracil: a comparative safety and efficacy report

PURPOSE

To report the long-term comparative outcomes for needle revision with 5-fluorouracil (5-FU) and mitomycin C (MMC) of failed trabeculectomy blebs.

PATIENTS AND METHODS

A retrospective database search was made for all patients who had needle revision with subconjunctival antimetabolite injections on the slit lamp from August 2001 to April 2006. Needle revisions were augmented with MMC instead of 5-FU from December 2003. Ninety-eight eyes of 95 consecutive patients (45 with MMC and 53 with 5-FU) with a minimum follow-up of 1 year were included. 5-FU (5 mg) or MMC (0.02 mg), with 0.1 mL of 2% lignocaine was injected subconjunctivally at least 10 minutes before the revision procedure in the clinic. No patient from the MMC group received subsequent 5-FU injections.

RESULTS

The 5-FU group had significantly longer mean follow-ups (P<0.001) of 53.0+/-18.12 months compared with 33.3+/-9.0 months in the MMC group. The 5-FU group had a significantly higher number of needle revisions than MMC group (1.9+/-1.0 vs. 1.2+/-0.5, P=0.001). Twenty-five eyes (47%) of the 5-FU group and 36 eyes (80%) of the MMC group had a single needle revision (P=0.009). The probability of maintaining intraocular pressure between 5 and 16 mm Hg with no glaucoma medication or further surgical procedure was 71% (62%-88%) and 45% (33%-60%) at 1 year and 61% (49%-78%) and 30% (20%-46%) at 2 years in the MMC and 5-FU groups, respectively. MMC use (hazard ratio=2.18, 95% confidence interval, 1.25-3.81, P=0.006) and intraocular pressure drop immediately after needling as a continuous variable (hazard ratio=1.06, 95% confidence interval, 1.00-1.13.8, P=0.03) were significantly associated with success. Twelve eyes (22.6%) with failed 5-FU needling had subsequent MMC needle revisions, 5 of which were successful by the study criterion. Eyes with 5-FU needle revision were more likely to fail within the first 6 months (P=0.02). Serious complications included blebitis in 3 (5.7%) and 1 (2.2%), delayed bleb leaks in 9 (17.0%) and 1 (2.2%) eyes in the 5-FU and MMC groups, respectively. There was no statistical difference in the complication rates between the groups. Aqueous misdirection was observed in 1 (2.2%) eye of MMC group and delayed suprachoroidal hemorrhage in 1 (1.9%) eye of 5-FU group.

CONCLUSIONS

This study suggests that MMC is more effective than 5-FU for needle revision of failed trabeculectomy blebs.

The filtering, clear-cornea diathermal keratostomy: a minor Danish multicenter study

PURPOSE

Is the new micropenetrating, clear-cornea procedure, intrastromal diathermal keratostomy (IDK), an alternative to the intricate "modern trabeculectomy"?

METHODS

Prospective multicenter study. Four surgeons from 4 Danish eye departments attended an IDK course and subsequently decided when to start their consecutive IDK series. The data were analyzed centrally. Injection of preoperative, subconjunctival doses of mitomycin C (MMC) was recommended according to risk-of-failure. A total of 54 eyes from 48 patients with advanced and complicated glaucomas (mean age 65 y) and preoperative mean intraocular pressure (IOP) of 29 mm Hg were studied.

RESULTS

At 10 months (range: 3 to 34 mo) the total success rate, employing traditional IOP success criteria (IOP< or =18 mm Hg and postoperative IOP decrease > or =30%), was 87% (47 of 54 eyes). In the 69% (37 of 54 eyes) without medication, the final IOP+/-SD was 11+/-3.5 mm Hg. Employing new IOP success criteria (IOP< or =15 mm Hg and postoperative IOP decrease> or =30%) for severe glaucoma (cup/disc ratio> or =0.8) and traditional criteria for moderate glaucoma (cup/disc ratio< or =0.7) the success rates were 76% and 80% and the mean postoperative IOP+/-SD were 10+/-2.5 mm Hg and 13+/-2.5 mm Hg, respectively. No serious complications (malignant glaucoma, endophthalmitis) were seen. The success rate for the most experienced and the less experienced surgeons, with risk-of-failure factors per eye of 1.3 and 1.2, was similar at 88% and 86%, respectively. The "knife time" for the experienced surgeon averaged 15 minutes (range: 10 to 20 min). The success rate (traditional criteria) after IDK revision with internal needling was 69%.

CONCLUSIONS

MMC IDK seems to be simpler and quicker than the modern trabeculectomy, and with similar success rate and safety. Revision by internal needling is easy and efficient. Thus, MMC IDK may be a valid alternative and may also be recommended after failed MMC trabeculectomy, replacing shunting. Randomized, controlled studies are indicated.

Intrastromal diathermal keratostomy: a new micropenetrating clear-cornea glaucoma procedure

PURPOSE

The filtering intrastromal diathermal keratostomy (IDK) was developed to comply with the call for a low postoperative intraocular pressure (IOP) and a bleb morphology without a thin, cystic appearance.

PATIENTS AND METHODS

A diathermal microkeratostomy (150 to 200 microm) was created into the anterior chamber, anterior to the Schwalbe line through the floor of a surgical corneoscleral tunnel incision into the subconjunctival space. A newly developed, bipolar diathermal microneedle was used to create the keratostomy, replacing the Holmium laser used previously. Subconjunctival injections of 3 microg mitomycin C were used in each eye 1 week before the IDK to obtain maximum antiproliferative effect at the time of the operation. Nine patients (10 eyes) with complicated, refractory primary and secondary open-angle glaucoma are discussed.

RESULTS

Histologic examination of the IDK and clinical postoperative ultrasound biomicroscopy showed an optimal appearance of the diathermal microkeratostomy. After 34 months (range 24 to 42 mo) the mean IOP was 11 mm Hg (SD+/-3, range 6 to 16) without medication in all 10 eyes. IDK revision with internal needling of postoperative subconjunctival fibrosis through the tunnel incision was performed in 5 eyes after an average of 3 months (range 0.2 to 7 mo). After 33 months (range 19 to 38 mo), the postrevision mean IOP was 10 mm Hg (SD+/-2, range 8 to 14) without medication in all 5 eyes. All 10 eyes showed noncystic diffuse blebs with optimal spongy subepithelial morphology: in 2 eyes the blebs were totally avascular and in 8 eyes they were relatively avascular.

CONCLUSIONS

The preliminary results of the new clear-cornea IDK seem promising because of postoperative IOP of about 10 mm Hg despite a low dose of mitomycin C and noncystic bleb morphology.