Paulo Falabella

Stem cell based therapies for age-related macular degeneration: The promises and the challenges

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly in developed countries. AMD is classified as either neovascular (NV-AMD) or non-neovascular (NNV-AMD). Cumulative damage to the retinal pigment epithelium, Bruchs membrane, and choriocapillaris leads to dysfunction and loss of RPE cells. This causes degeneration of the overlying photoreceptors and consequential vision loss in advanced NNV-AMD (Geographic Atrophy). In NV-AMD, abnormal growth of capillaries under the retina and RPE, which leads to hemorrhage and fluid leakage, is the main cause of photoreceptor damage. Although a number of drugs (e.g., anti-VEGF) are in use for NV-AMD, there is currently no treatment for advanced NNV-AMD. However, replacing dead or dysfunctional RPE with healthy RPE has been shown to rescue dying photoreceptors and improve vision in animal models of retinal degeneration and possibly in AMD patients. Differentiation of RPE from human embryonic stem cells (hESC-RPE) and from induced pluripotent stem cells (iPSC-RPE) has created a potentially unlimited source for replacing dead or dying RPE. Such cells have been shown to incorporate into the degenerating retina and result in anatomic and functional improvement. However, major ethical, regulatory, safety, and technical challenges have yet to be overcome before stem cell-based therapies can be used in standard treatments. This review outlines the current knowledge surrounding the application of hESC-RPE and iPSC-RPE in AMD. Following an introduction on the pathogenesis and available treatments of AMD, methods to generate stem cell-derived RPE, immune reaction against such cells, and approaches to deliver desired cells into the eye will be explored along with broader issues of efficacy and safety. Lastly, strategies to improve these stem cell-based treatments will be discussed.

Anti-VEGF for the Management of Diabetic Macular Edema

Diabetic retinopathy (DR) is an important cause of vision loss around the world, being the leading cause in the population between 20 and 60 years old. Among patients with DR, diabetic macular edema (DME) is the most frequent cause of vision impairment and represents a significant public health issue. Macular photocoagulation has been the standard treatment for this condition reducing the risk of moderate visual loss by approximately 50%. The role of vascular endothelial growth factor (VEGF) in DR and DME pathogenesis has been demonstrated in recent studies. This review addresses and summarizes data from the clinical trials that investigated anti-VEGF for the management of DME and evaluates their impact on clinical practice. The literature searches were conducted between August and October 2013 in PubMed and Cochrane Library with no date restrictions and went through the most relevant studies on pegaptanib, ranibizumab, bevacizumab, and aflibercept for the management of DME. The efficacy and safety of intravitreal anti-VEGF as therapy for DME have recently been proved by various clinical trials providing significantly positive visual and anatomical results. Regarding clinical practice, those outcomes have placed intravitreal injection of anti-VEGF as an option that must be considered for the treatment of DME.

Ten-Year Follow-up of a Blind Patient Chronically Implanted with Epiretinal Prosthesis Argus I

PURPOSE The Argus I implant is the first-generation epiretinal prosthesis approved for an investigational clinical trial by the United States Food and Drug Administration. Herein we report testing results obtained from a 10-year follow-up to study the physiologic effects of the bioelectronic visual implant after prolonged chronic electrical stimulation. DESIGN Case report. PARTICIPANT One man, 55 years of age when enrolled in the study, underwent surgical implantation of the Argus I in June 2004, followed by periodic tests from July 2004 through June 2014, spanning a total of 10 years. METHODS The decade-long follow-up consisted of implant system performance tests, subject visual function evaluation, and implant-retina interface analysis. MAIN OUTCOME MEASURES Changes in electrode impedance and perceptual threshold over the time course; subjects performance on visual function task, orientation, and mobility tests; and optical coherence tomography data, fundus imaging, and fluorescein angiography results for the assessment of subjects implant-retina physical interface. RESULTS Electrically elicited phosphenes were present 10 years after implantation of an epiretinal stimulator. The test subject not only was able to perceive phosphenes, but also could perform visual tasks at rates well above chance. CONCLUSIONS This decade-long follow-up report provides further support for the use of retinal prostheses as a long-lasting treatment for some types of blindness.

Profile of ocriplasmin and its potential in the treatment of vitreomacular adhesion.

The recent approval by the US Food and Drug Administration of ocriplasmin for the treatment of symptomatic vitreomacular adhesion (VMA), often associated with vitreomacular traction (VMT) and macular hole (MH), has brought new attention to the field of pharmacologic vitreolysis. The need for an enzyme to split the vitreomacular interface, which is formed by a strong adhesive interaction between the posterior vitreous cortex and the internal limiting membrane, historically stems from pediatric eye surgery. This review summarizes the different anatomic classifications of posterior vitreous detachment or anomalous posterior vitreous detachment and puts these in the context of clinical pathologies commonly observed in clinical practice of the vitreoretinal specialist, such as MH, VMT, age-related macular degeneration, and diabetic macular edema. We revisit the outcome of the Phase II studies that indicated ocriplasmin was a safe and effective treatment for selected cases of symptomatic VMA and MH. Release of VMA at day 28 was achieved by 26.5% of patients in the ocriplasmin group versus 10.1% in the placebo group (P<0.001). Interestingly, for MHs, the numbers were more remarkable. Predictive factors for successful ocriplasmin treatment were identified for VMT (VMA diameter smaller than 1,500 μm) and MH (smaller than 250 μm). In comparison with the highly predictable outcome after vitrectomy, the general success rate of ocriplasmin not under clinical trial conditions has not fully met expectations and needs to be proven in real-world clinical settings. The ocriplasmin data will be compared in the future with observational data on spontaneous VMA release, will help retina specialists make more accurate predictions, and will improve outcome rates.

Survival and Functionality of hESC-Derived Retinal Pigment Epithelium Cells Cultured as a Monolayer on Polymer Substrates Transplanted in RCS Rats.

PURPOSE To determine the safety, survival, and functionality of human embryonic stem cell-derived RPE (hESC-RPE) cells seeded on a polymeric substrate (rCPCB-RPE1 implant) and implanted into the subretinal (SR) space of Royal College of Surgeons (RCS) rats. METHODS Monolayers of hESC-RPE cells cultured on parylene membrane were transplanted into the SR space of 4-week-old RCS rats. Group 1 (n = 46) received vitronectin-coated parylene membrane without cells (rMSPM+VN), group 2 (n = 59) received rCPCB-RPE1 implants, and group 3 (n = 13) served as the control group. Animals that are selected based on optical coherence tomography screening were subjected to visual function assays using optokinetic (OKN) testing and superior colliculus (SC) electrophysiology. At approximately 25 weeks of age (21 weeks after surgery), the eyes were examined histologically for cell survival, phagocytosis, and local toxicity. RESULTS Eighty-seven percent of the rCPCB-RPE1-implanted animals showed hESC-RPE survivability. Significant numbers of outer nuclear layer cells were rescued in both group 1 (rMSPM+VN) and group 2 (rCPCB-RPE1) animals. A significantly higher ratio of rod photoreceptor cells to cone photoreceptor cells was found in the rCPCB-RPE1-implanted group. Animals with rCPCB-RPE1 implant showed hESC-RPE cells containing rhodopsin-positive particles in immunohistochemistry, suggesting phagocytic function. Superior colliculus mapping data demonstrated that a significantly higher number of SC sites responded to light stimulus at a lower luminance threshold level in the rCPCB-RPE1-implanted group. Optokinetic data suggested both implantation groups showed improved visual acuity. CONCLUSIONS These results demonstrate the safety, survival, and functionality of the hESC-RPE monolayer transplantation in an RPE dysfunction rat model.

Comparison of Reaction Response Time between Hand and Foot Controlled Devices in Simulated Microsurgical Testing

Purpose. We hypothesized that reaction times (RTs) for a switch release are faster for hand-controlled than for foot-controlled switches for physiological and anatomical reasons (e.g., nerve conduction speed). The risk of accidental trauma could be reduced if the surgeon reacted quicker and therefore improve the surgical outcome. Method. We included 47 medical professionals at USC. Demographics and handedness were recorded. Under a microscope, a simple reaction time test was performed, testing all extremities multiple times in a random order. Additionally, a subjective questionnaire was administered. Results. The mean RTs for hands are 318.24 ms ± 51.13 and feet 328.69 ± 48.70. The comparison of hand versus foot showed significant shorter RTs for the hand (P = 0.025). Partially significant differences between and within the experience level groups could be demonstrated by level of education (LE) and microscopic surgeries/week (MSW) (P = 0.57–0.02). In the subjective questionnaire, 91.5% (n = 43/47) of test subjects prefer to use hand controls. Conclusion. Our data show that the RT for hands is faster than feet. Similarly the subjective questionnaire showed a greater preference for hand actuation. This data suggest a hand-controlled ophthalmic instrument might have distinct advantages; however, clinical correlation is required.

An Innovative Surgical Technique for Subretinal Transplantation of Human Embryonic Stem Cell-Derived Retinal Pigmented Epithelium in Yucatan Mini Pigs: Preliminary Results

BACKGROUND AND OBJECTIVE To develop a safe and efficient surgical procedure for subretinal implantation into porcine eyes of a human embryonic stem cell-derived retinal pigmented epithelium (hESC-RPE) monolayer seeded onto a Parylene-C scaffold. This implant is referred to as CPCB-RPE1. MATERIALS AND METHODS Ultrathin Parylene-C scaffolds were seeded with hESC-RPE and surgically implanted into the subretinal space of Yucatan mini pigs (n = 8). The surgery consisted of pars plana vitrectomy, induction of a limited retinal detachment, and peripheral retinotomy for insertion of the monolayer using a novel tissue injector, followed by silicone oil tamponade injection, laser photocoagulation around the retinotomy site, and inferior iridectomy. Oral cyclosporine was administered from day 1 and during the entire follow-up period. Three months later, the animals were euthanized and the eyes and major organs were submitted for histological analysis. Adjacent sections underwent immunohistochemical analysis to detect human cells using anti-TRA-1-85 (human blood group antigen) antibody and DAPI antibodies. RESULTS The cell monolayer was immunopositive for TRA-1-85 3 months after implantation and migration from the Parylene-C scaffold was not detected. One eye had a mild inflammatory reaction around the implant that was negative for human biomarkers. No intraocular or systemic tumors were detected. CONCLUSION The hESC-RPE cells survived for 3 months in this animal model. The surgical procedure for subretinal implantation of CPCB-RPE1 is feasible and safe, without cell migration off the scaffold or development of ocular or systemic tumors.

Fluidics comparison between dual pneumatic and spring return high-speed vitrectomy systems.

BACKGROUND AND OBJECTIVE To compare the water and vitreous flow rates and duty cycle (DC) between two ultrahigh-speed vitrectomy systems: pneumatic with spring return (SR) and dual pneumatic (DP) probes. MATERIALS AND METHODS The flow rate was calculated using a high-sampling precision balance that measured the mass of water and vitreous removed from a vial by a vitreous cutter. Frame-by-frame analysis of a high-speed video of the cutter was used to determine the DC. Three cutters of each gauge (20, 23, and 25 G) were tested with an SR and a DP system using the standard DC setting (biased open) at 0 (water only), 1,000, 2,000, 3,000, 4,000, and 5,000 cuts per minute (CPM) with aspiration levels of 100, 200, 300, 400, 500, and 600 mm Hg. RESULTS The DC was slightly higher with the SR system using most parameters and gauges although without statistical significance. The water flow rate was somewhat higher with the SR system, except for 25 G with 4,000 and 5,000 CPM. The vitreous flow rate was similar using most parameters, with the SR system showing higher flows at lower cut rates (1,000-3,000 CPM). CONCLUSIONS SR and DP systems produced similar water and vitreous flow rates. Additional studies in human eyes are necessary to confirm these findings.

Retinal Prostheses: A Clinical Perspective

Artificial vision is restoring sight by electrical stimulation of the visual system at the level of retina, optic nerve, lateral geniculate body, or occipital cortex. The development of artificial vision began with occipital cortex prosthesis; however, retinal prosthesis has advanced faster in recent years. Currently, multiple efforts are focused on finding the optimal approach for restoring vision through an implantable retinal microelectrode array system. Retinal prostheses function by stimulating the inner retinal neurons that survive retinal degeneration. In these devices, the visual information, gathered by a light detector, is transformed into controlled patterns of electrical pulses, which are in turn delivered to the surviving retinal neurons by an electrode array. Retinal prostheses are classified based on where the stimulating array is implanted (ie, epiretinal, subretinal, suprachoroidal, or episcleral). Recent regulatory approval of 2 retinal prostheses has greatly escalated interest in the potential of these devices to treat blindness secondary to outer retinal degeneration. This review will focus on the technical and operational features and functional outcomes of clinically tested retinal prostheses. We will discuss the major barriers and some of the more promising solutions to improve the outcomes of restoring vision with electrical retinal stimulation.

INTRAOCULAR PRESSURE CHANGES DURING VITRECTOMY USING CONSTELLATION VISION SYSTEM'S INTRAOCULAR PRESSURE CONTROL FEATURE.

Purpose: To evaluate intraocular pressure (IOP) changes during experimental vitrectomy and the efficacy of Constellation Vision Systems IOP control (IOPc) feature in reestablishing baseline pressure. Methods: Using a pressure transducer in freshly enucleated porcine eyes, a broad range of parameters (baseline pressures, aspiration levels, and cut rates) were tested with 23- and 25-gauge probes and IOPc turned ON versus OFF. Results: IOPc turned ON was significantly more effective than IOPc turned OFF in controlling IOP drop and stabilizing pressure during vitrectomy using a wide range of baseline pressures (20–70 mmHg). The 23-gauge system consistently presented a reduced drop from baseline compared with the 25-gauge system. The overall average drop for the 23- and 25-gauge systems was 12.79 mmHg and 21.17 mmHg, respectively. Both gauge sizes reestablished baseline pressure approximately 1.6 seconds after the initial pressure drop generated at the beginning of aspiration. A peak of IOP (overshooting) was observed when the pressure was returning to baseline using both 23- and 25-gauge systems. Conclusion: Using IOPc feature turned ON, 23- and 25-gauge probes were effective in reestablishing and sustaining baseline infusion pressures, although 23-gauge probes showed less IOP fluctuation than did 25-gauge probes.