Jean H.M. Feyen

Robot-assisted retinal vein cannulation in an in vivo porcine retinal vein occlusion model

To evaluate the feasibility of robot‐assisted retinal vein cannulation for retinal vein occlusion.

Intravitreally Injected Fluid Dispersion: Importance of Injection Technique

Purpose The purpose of this study was to evaluate the dispersion of intravitreally injected solutions and investigate the influence of varying injection techniques. Methods This was a prospective study using enucleated porcine eyes and ultra-high-resolution computed tomography (UHRCT) scanning to visualize iomeprol intravitreal dispersion. Sixty eyes were divided over 12 different groups according to the injection procedure: fast (2 seconds) or slow (10 seconds) injection speed and needle tip location (6- and 12-mm needle shaft insertion or premacular tip placement verified by indirect ophthalmoscopy). For each of these combinations, eyes were either injected with the combination of V20I (which is an analogue of ocriplasmin) and iomeprol or iomeprol alone. Distance to the macula and volume measurements were performed at 1, 2, 3, and 5 hours after injection. Results The measured contrast bolus volume increases slowly over time to an average of 0.70 (P = 0.03), 1.04 (P = 0.006), and 0.79 (P = 0.0001) cm3 5 hours after the injection for the 6-mm needle shaft insertion, 12-mm needle shaft insertion, and premacular needle tip placement, respectively. The distance to the macular marker was significantly lower for premacular needle tip placement injections compared with 6- and 12-mm needle shaft insertion depths. Conclusions Ultra-high-resolution computed tomography with three-dimensional reconstruction offers the possibility to study the dispersion of intravitreally injected solutions in a noninvasive manner. Intravitreal premacular solution delivery is possible with an indirect ophthalmoscope-guided injection technique and significantly reduces the time to reach the posterior pole in respect to 6- and 12-mm needle insertion depths. The speed of injection does not influence dispersion significantly.

The Combination of PlGF Inhibition and MMC as a Novel Anti-Scarring Strategy for Glaucoma Filtration Surgery

PURPOSE The complementary effects of mitomycin-C (MMC) and anti-placental growth factor (PlGF) therapy were explored and compared to the combined administration of MMC and aflibercept. Additionally, the effect of PlGF (inhibition) on IOP was investigated, since aqueous PlGF is known to be upregulated in glaucoma patients. METHODS In the trabeculectomy mouse model, intracameral injection(s) of the PlGF inhibitor (5D11D4) were compared to MMC or aflibercept and to the combination of both compounds. Treatment outcome was studied by bleb investigation and by Sirius Red staining. The effect of subconjunctival PlGF administration and topical 5D11D4 on IOP was investigated in normotensive mice and was compared to topical administration of latanoprost, the gold standard for IOP-lowering. RESULTS Combination of MMC and 5D11D4 was able to significantly improve surgical outcome compared to monotherapy of MMC or 5D11D4 (n = 20; P < 0.001). Compared to combined treatment of MMC with aflibercept, the simultaneous administration of MMC and 5D11D4 was equally efficacious in improving surgical outcome (n = 15; P = 0.88). In normotensive mice, 5D11D4 was able to significantly reduce the IOP-elevation induced by PlGF (n = 10; P < 0.05), whereas no effect of 5D11D4 was seen in naive mice, which was in contrast to latanoprost. CONCLUSIONS The current data suggest that application of MMC together with PlGF inhibition may have complementary effects in the improvement of surgical outcome and is equally efficacious as the combined treatment of MMC and aflibercept. Inhibition of PlGF also might open alternative perspectives as IOP-lowering strategy for glaucoma patients with increased aqueous PlGF levels.

Stable and Long-Lasting, Novel Bicyclic Peptide Plasma Kallikrein Inhibitors for the Treatment of Diabetic Macular Edema

Plasma kallikrein, a member of the kallikrein-kinin system, catalyzes the release of the bioactive peptide bradykinin, which induces inflammation, vasodilation, vessel permeability, and pain. Preclinical evidence implicates the activity of plasma kallikrein in diabetic retinopathy, which is a leading cause of visual loss in patients suffering from diabetes mellitus. Employing a technology based on phage-display combined with chemical cyclization, we have identified highly selective bicyclic peptide inhibitors with nano- and picomolar potencies toward plasma kallikrein. Stability in biological matrices was either intrinsic to the peptide or engineered via the introduction of non-natural amino acids and nonpeptidic bonds. The peptides prevented bradykinin release in vitro, and in vivo efficacy was demonstrated in both a rat paw edema model and in rodent models of diabetes-induced retinal permeability. With a highly extended half-life of ∼40 h in rabbit eyes following intravitreal administration, the bicyclic peptides are promising novel agents for the treatment of diabetic retinopathy and diabetic macular edema.

Assessment of Ocriplasmin Effects on the Vitreoretinal Compartment in Porcine and Human Model Systems

Ocriplasmin (Jetrea®) is a recombinant protease used to treat vitreomacular traction. To gain insight into vitreoretinal observations reported after ocriplasmin treatment, we have developed an in vivo porcine ocriplasmin-induced posterior vitreous detachment (PVD) model in which we investigated vitreoretinal tissues by optical coherence tomography, histology, and cytokine profiling. Eight weeks postinjection, ocriplasmin yielded PVD in 82% of eyes. Subretinal fluid (85%) and vitreous hyperreflective spots (45%) were resolved by week 3. Histological analysis of extracellular matrix (ECM) proteins such as laminin, fibronectin, and collagen IV indicated no retinal ocriplasmin-induced ECM distribution changes. Retinal morphology was unaffected in all eyes. Cytokine profiles of ocriplasmin-treated eyes were not different from vehicle. In cell-based electrical resistance assays, blood-retinal barrier permeability was altered by ocriplasmin concentrations of 6 μg/mL and higher, with all effects being nontoxic, cell-type specific, and reversible. Ocriplasmin was actively taken up by RPE and Müller cells, and our data suggest both lysosomal and transcellular clearance routes for ocriplasmin. In conclusion, transient hyperreflective spots and fluid in a porcine ocriplasmin-induced PVD model did not correlate with retinal ECM rearrangement nor inflammation. Reversible in vitro effects on blood-retinal barrier permeability provide grounds for a hypothesis on the mechanisms behind transient subretinal fluid observed in ocriplasmin-treated patients.