Retinal pigment epithelial repopulation in monkeys after submacular surgery

Visualizing advances in the future of primate neuroscience research

Future neuroscience and biomedical projects involving non-human primates (NHPs) remain essential in our endeavors to understand the complexities and functioning of the mammalian central nervous system. In so doing, the NHP neuroscience researcher must be allowed to incorporate state-of-the-art technologies, including the use of novel viral vectors, gene therapy and transgenic approaches to answer continuing and emerging research questions that can only be addressed in NHP research models. This perspective piece captures these emerging technologies and some specific research questions they can address. At the same time, we highlight some current caveats to global NHP research and collaborations including the lack of common ethical and regulatory frameworks for NHP research, the limitations involving animal transportation and exports, and the ongoing influence of activist groups opposed to NHP research.

Selective Large-Area Retinal Pigment Epithelial Removal by Microsecond Laser in Preparation for Cell Therapy

Purpose

Cell therapy is a promising treatment for retinal pigment epithelium (RPE)-associated eye diseases such as age-related macular degeneration. Herein, selective microsecond laser irradiation targeting RPE cells was used for minimally invasive, large-area RPE removal in preparation for delivery of retinal cell therapeutics.

Methods

Ten rabbit eyes were exposed to laser pulses 8, 12, 16, and 20 µs in duration (wavelength, 532 nm; top-hat beam profile, 223 × 223 µm²). Post-irradiation retinal changes were assessed with fluorescein angiography (FA), indocyanine green angiography (ICGA), and optical coherence tomography (OCT). RPE viability was evaluated with an angiographic probit model. Following vitrectomy, a subretinal injection of balanced salt solution was performed over a lasered (maximum 13.6 mm2) and untreated control area. Bleb retinal detachment (bRD) morphology was then evaluated by intraoperative OCT.

Results

Within 1 hour after irradiation, laser lesions showed FA and ICGA leakage. OCT revealed that large-area laser damage was limited to the RPE. The angiographic median effective dose irradiation thresholds (ED50) were 45 µJ (90 mJ/cm2) at 8 µs, 52 µJ (104 mJ/cm2) at 12 µs, 59 µJ (118 mJ/cm2) at 16 µs, and 71 µJ (142 mJ/cm2) at 20 µs. Subretinal injection over the lasered area resulted in a controlled, shallow bRD rise, whereas control blebs were convex in shape, with less predictable spread.

Conclusions

Large-area, laser-based removal of host RPE without visible photoreceptor damage is possible and facilitates surgical retinal detachment.

Translational Relevance

Selective microsecond laser-based, large-area RPE removal prior to retinal cell therapy may reduce iatrogenic trauma.

Optical coherence tomography features of the repair tissue following RPE tear and their correlation with visual outcomes

To assess the optical coherence tomography (OCT) features of the repair tissue after retinal pigment epithelial (RPE) tear in neovascular age-related macular degeneration. Retrospective, observational study. Medical and imaging records of patients that developed tears after starting anti-VEGF treatment and with at least 12 months of follow-up were reviewed. OCT reflectivity of the RPE-subretinal hyperreflective tissue (SHT) complex was measured at 6, 12 and 18 months (when available). Reflectivity of the adjacent unaffected RPE-Bruch’s membrane was taken as internal reference. Other variables: grade and rip occurrence (early/late); number of intravitreal injections; type of macular neovascularization; sub-macular hemorrhage (SMH) at onset. Forty-nine eyes (age: 76.1 ± 7.0 years; VA: 0.54 ± 0.27 LogMAR) were included. Thirty-eight eyes had OCT signs of healing during the follow-up, with 21 showing SMH at baseline. Final VA positively correlated with the number of injections and negatively correlated with the RPE-SHT reflectivity and the presence of SMH (p < 0.001). Reflectivity of the RPE-SHT complex was positively associated with time and SMH at baseline (p < 0.05). In our study, most eyes showed signs of tissue repair after RPE tear. The reflectivity of repair tissue, the SMH presence and the number of anti-VEGF injections appeared to be major predictors of visual outcomes.

Choroidal and Retinal Changes After Systemic Adrenaline and Photodynamic Therapy in Non-Human Primates

Purpose

To determine the tomographic, angiographic, and histologic changes in the choroid and retina of cynomolgus monkeys after systemic adrenaline and verteporfin photodynamic therapy (vPDT).

Methods

Six cynomolgus monkeys (12 eyes) were treated with vPDT only (n = 2), adrenaline only for eight weeks (n = 2), adrenaline for eight weeks with vPDT at week 4 (n = 4), and adrenaline for 12 weeks and vPDT at week 8 (n = 4). Spectral-domain optical coherence tomography, angiography, and autofluorescence were performed at baseline and every 14 days thereafter until 28 days after adrenaline therapy or vPDT. Choroid parameters included choroidal thickness (CT) changes and structural changes using semiautomated image binarization. Histology with light and electron microscopy was performed.

Results

Adrenaline resulted in subfoveal CT increase at week 4 compared with baseline (3.4%, P = 0.010), with further increase at week 8 (3.9%, P = 0.007). This correlated with choroidal luminal area increase (16.0% at week 8 compared with baseline, P = 0.030). Outer retinal changes included subretinal fluid, ellipsoid zone (EZ) disruption, photoreceptor elongation, and sub/intraretinal bright dots. Hypocyanescent spots surrounded by leakage was observed. Histology showed dilated choroidal vessels, intracytoplasmic vacuoles, and retinal pigment epithelium (RPE) enlarged basal infoldings. The vPDT decreased subfoveal CT at four weeks after vPDT (−7.5%, P = 0.007). This correlated with choroidal stromal area decrease (−18.0%, P < 0.010). Within the treatment spot, there was outer retinal atrophy, EZ disruption, irregular RPE thickening, intense hypoautofluorescence, hyperfluorescence, and hypocyanescence. On histology, there were outer retina, RPE, and choroid changes.

Conclusions

Adrenaline induces choroidal vessel dilation and CT increase. The vPDT decreases CT because of a reduction in choroidal stromal component.

Hints for Gentle Submacular Injection in Non-Human Primates Based on Intraoperative OCT Guidance

Purpose

Delivery of Advanced Therapy Medicinal Products to the submacular space is increasingly evolving into a therapeutic modality. Cell replacement for age-related macular degeneration (AMD) and gene therapy for RPE65 are recent successful examples. Herein, a nonhuman primate (NHP) model was used to investigate surgical means to detach the macula.

Methods

Sixteen eyes of 13 healthy macaques underwent a 25-gauge vitrectomy and subretinal injection of balanced salt solution monitored by microscope-integrated intraoperative optical coherence tomography (miOCT). The animals were followed with OCT and histology.

Results

The miOCT monitoring allowed a more precise definition of surgical trauma ranging from an initial full-thickness foveal tear, or induction of a cystoid macular edema (CME), until no foveal defect was discernible, as the technique improved. However, as the subretinal fluid wave detached the fovea, the aforementioned lesions formed, whereas persistent retinal adhesion reproducibly proved to remain in the distal parafoveal semi-annulus. Measures to reduce foveal trauma during submacular fluid injection included reducing intraocular pressure, injection volume, and velocity, as well as the retinal location for bleb initiation, use of a vitreous tamponade, and a dual-bore subretinal cannula.

Conclusions

A stable very low intraocular pressure and careful subretinal injection may avoid tangential macular stretching or mechanical CME formation, while vitreous tamponade may facilitate a more lamellar subretinal flow, all thereby reducing foveal trauma during submacular injection in NHP.

Translational Relevance

These results can be relevant to any submacular surgery procedure used today, as they synergistically reduce the risk of compromising foveal integrity.

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy

PURPOSE

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits.

METHODS

Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment.

RESULTS

We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment.

CONCLUSIONS

Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

Retinal pigment epithelial tears

A retinal pigment epithelial (RPE) tear is a well-known complication of retinal pigment epithelial detachments (PED) and may cause a significant visual impairment. The most common cause is a vascularized PED in patients with exudative age-related macular degeneration (AMD). The development of diagnostic imaging techniques brings us closer to the etiology and pathophysiological mechanisms of this entity, offering us new strategies for treatment and follow-up. The advent of intravitreal antiangiogenic treatment (anti-VEGF) has led to an increase in the number of reported cases of RPE tears, which are an important vision-limiting factor during treatment. However, RPE tears may occur spontaneously or as a consequence of thermal laser treatment, photodynamic therapy or anti-VEGF therapy. It is accepted that the mechanism of RPE tears is multifactorial. The optimization of the functional outcome of this complication has been described with continuous treatment with antiangiogenic drugs. The goal of the present review is to evaluate the incidence, risk factors and treatment of RPE tears.

Transplantation of Retinal Pigment Epithelium Using Viable Cryopreserved Cells

Transplantation of retinal pigment epithelium (RPE) may have potential clinical application for the surgical treatment of RPE-specific retinal degeneration, including age-related macular degeneration. The feasibility of an RPE storage bank has been investigated by experimenting with transplantation using viable, cryopreserved RPE cells. Fresh and cultured fetal human and bovine RPE cells were cryopreserved in 90% fetal bovine serum containing 10% dimethyl sulfoxide. The viability of the cells before and after cryopreservation was evaluated by trypan blue dye exclusion test, microculture tetrazolium assay (MTA), tissue culture, and transplantation after cryopreservation. The origin of RPE cells before and after cryopreservation was assessed by immunocytochemistry, immunoblotting, and indirect ELISA of RPE-marker protein using cytokeratin for cultured fetal human RPE cells and by immunocytochemistry of cellular retinaldehyde-binding protein (CR-ALBP) for cultured bovine RPE cells. Freshly isolated and cryopreserved uncultured bovine RPE cells were transplanted by posterior transscleral approach into the subretinal spaces of adult albino rabbits and 23-day-old Royal College of Surgeons (RCS) rats with a 33 gauge Hamilton syringe. Following surgery, artificial retinal blebs were confirmed by fundus examination. Morphologic examination was performed postoperatively by light and electron microscopy in albino rabbits and by light microscopy in RCS rats up to 3 mo. Control subretinal injections using vehicle solution also were performed in RCS rats. Cultured fetal human and bovine RPE cells after cryopreservation were found to be viable, based on the results of trypan blue dye exclusion test, MTA, tissue culture, and transplantation. Expression and reexpression of cytokeratin intermediate filaments in cultured fetal human RPE were demonstrated by immunocytochemistry, immunoblotting, and indirect ELISA before and after cryopreservation. Immunocytochemistry of CRALBP before and after cryopreservation in uncultured bovine RPE cells disclosed expression and reexpression of RPE cell marker protein. No uncultured fetal human RPE cells showed proliferation in tissue culture after cryopreservation. In rabbits, light and electron microscopy disclosed xenografted RPE cells residing on Bruch's membrane of the host retina. No sign of graft vs. host reaction was observed. No morphologic difference was noted between the fresh and 10-day-old cryopreserved RPE cells in situ following transplantation at day 25. In RCS rats, subretinal injection of 3-wk-old cryopreserved bovine RPE cells partially rescued photoreceptor cells locally at the transplanted area observed at 3 mo postoperatively. The retinal photoreceptors at the inferior hemisphere of the transplanted eye and the eye injected with vehicle solution showed no rescue effect. We found that cryopreserved cultured fetal human RPE cells and uncultured and cultured bovine RPE cells can be used for RPE transplantation studies. The ability to create an RPE storage bank as a source of donor cells may result in several clinical advantages.

Potential of Induced Pluripotent Stem Cells (iPSCs) for Treating Age-Related Macular Degeneration (AMD)

The field of stem cell biology has rapidly evolved in the last few decades. In the area of regenerative medicine, clinical applications using stem cells hold the potential to be a powerful tool in the treatment of a wide variety of diseases, in particular, disorders of the eye. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are promising technologies that can potentially provide an unlimited source of cells for cell replacement therapy in the treatment of retinal degenerative disorders such as age-related macular degeneration (AMD), Stargardt disease, and other disorders. ESCs and iPSCs have been used to generate retinal pigment epithelium (RPE) cells and their functional behavior has been tested in vitro and in vivo in animal models. Additionally, iPSC-derived RPE cells provide an autologous source of cells for therapeutic use, as well as allow for novel approaches in disease modeling and drug development platforms. Clinical trials are currently testing the safety and efficacy of these cells in patients with AMD. In this review, the current status of iPSC disease modeling of AMD is discussed, as well as the challenges and potential of this technology as a viable option for cell replacement therapy in retinal degeneration.

Successful Transplantation of Retinal Pigment Epithelial Cells from MHC Homozygote iPSCs in MHC-Matched Models

There is an ongoing controversy as to whether major histocompatibility complex (MHC) matching is a solution for allogeneic stem cell transplantation. In the present study, we established retinal pigment epithelial (RPE) cells from induced pluripotent stem cells (iPSCs) in MHC homozygote donors. We observed no rejection signs in iPSC-derived RPE allografts of MHC-matched animal models without immunosuppression, whereas there were immune attacks around the graft and retinal tissue damage in MHC-mismatched models. In an immunohistochemical examination of MHC-mismatched allografts, the transplanted RPE sheets/cells were located in the subretinal space, but the RPE exhibited inflammatory and hypertrophic changes, and many inflammatory cells, e.g., Iba1⁺ cells, MHC class II⁺ cells, and CD3⁺ T cells, invaded the graft area. Conversely, these inflammatory cells poorly infiltrated the area around the transplanted retina if MHC-matched allografts were used. Thus, cells derived from MHC homozygous donors could be used to treat retinal diseases in histocompatible recipients.

Focal damage to macaque photoreceptors produces persistent visual loss

Insertion of light-gated channels into inner retina neurons restores neural light responses, light evoked potentials, visual optomotor responses and visually-guided maze behavior in mice blinded by retinal degeneration. This method of vision restoration bypasses damaged outer retina, providing stimulation directly to retinal ganglion cells in inner retina. The approach is similar to that of electronic visual protheses, but may offer some advantages, such as avoidance of complex surgery and direct targeting of many thousands of neurons. However, the promise of this technique for restoring human vision remains uncertain because rodent animal models, in which it has been largely developed, are not ideal for evaluating visual perception. On the other hand, psychophysical vision studies in macaque can be used to evaluate different approaches to vision restoration in humans. Furthermore, it has not been possible to test vision restoration in macaques, the optimal model for human-like vision, because there has been no macaque model of outer retina degeneration. In this study, we describe development of a macaque model of photoreceptor degeneration that can in future studies be used to test restoration of perception by visual prostheses. Our results show that perceptual deficits caused by focal light damage are restricted to locations at which photoreceptors are damaged, that optical coherence tomography (OCT) can be used to track such lesions, and that adaptive optics retinal imaging, which we recently used for in vivo recording of ganglion cell function, can be used in future studies to examine these lesions.

A study on proliferation and behavior of retinal pigment epithelial cells on purified alginate films

BACKGROUND AND OBJECTIVES

Alginate, an anionic polysaccharide distributed widely in the cell walls of brown algae, is used in biomedical applications. However, alginate' s performance as a biomaterial, has limited by its several contamination such as endotoxins, proteins and polyphenols.

METHODS AND RESULTS

To overcome this problem, we have developed using modified Korbutt method for alginate purification. After purification, we made alginate films and used for retinal pigment epithelial cell (RPEs) regeneration. ARPE-19 cells were seeded in non-purified and purified alginate films, and then cell viability and proliferation were estimated by MTT assay and RT-PCR was performed to assess specific cell expression. ARPE-19 cell-loaded alginate films were evaluated specific protein expression by through AEC staining and we examined the cell adhesion by scanning electron micro scopy (SEM).

CONCLUSIONS

In this result, ARPE-19 cells in purified alginate films had higher cell proliferative rate and phenotypic expression than those on non-purified alginate films. The results suggest that purified alginate is useful for RPEs regeneration.

Iodoacetic acid, but not sodium iodate, creates an inducible swine model of photoreceptor damage

Our purpose was to find a method to create a large animal model of inducible photoreceptor damage. To this end, we tested in domestic swine the efficacy of two chemical toxins, known to create photoreceptor damage in other species: Iodoacetic Acid (IAA) and Sodium Iodate (NaIO(3)). Intravenous (IV) administration of NaIO(3) up to 90 mg/kg had no effect on retinal function and 110 mg/kg was lethal. IV administration of IAA (5-20 mg/kg) produced concentration-dependent changes in visual function as measured by full-field and multi-focal electroretinograms (ffERG and mfERG), and 30 mg/kg IAA was lethal. The IAA-induced effects measured at two weeks were stable through eight weeks post-injection, the last time point investigated. IAA at 7.5, 10, and 12 mg/kg produce a concentration-dependent reduction in both ffERG b-wave and mfERG N1-P1 amplitudes compared to baseline at all post-injection times. Comparisons of dark- and light-adapted ffERG b-wave amplitudes show a more significant loss of rod relative to cone function. The fundus of swine treated with ≥10 mg/kg IAA was abnormal with thinner retinal vessels and pale optic discs, and we found no evidence of bone spicule formation. Histological evaluations show concentration-dependent outer retinal damage that correlates with functional changes. We conclude that NaIO(3,) is not an effective toxin in swine. In contrast, IAA can be used to create a rapidly inducible, selective, stable and concentration-dependent model of photoreceptor damage in swine retina. Because of these attributes this large animal model of controlled photoreceptor damage should be useful in the investigation of treatments to replace damaged photoreceptors.

Effects of extracellular matrix and neighboring cells on induction of human embryonic stem cells into retinal or retinal pigment epithelial progenitors

To determine the effects of extracellular matrix and neighboring cells on the differentiation of human embryonic stem cells (hESC) into progenitors of retinal cells and/or retinal pigment epithelium (RPE). HESC were cultured on mouse PA6 stromal cells for approximately 2weeks to obtain neural progenitors. To induce photoreceptor marker expression, the neural progenitors were cultured on a confluent monolayer of ARPE19 or on laminin-coated dishes. To induce RPE markers, the neural progenitors were seeded onto human Bruch's membrane or Matrigel. Cells were examined morphologically and stained with different RPE or neural progenitor markers. Microarray techniques were used to compare the gene expression profiles of hESC cultured on mouse fibroblasts or neural progenitors on PA6 cells to the transcriptome of the adult neural retina and RPE. HESC cultured on PA6 cells expressed neural progenitor markers beta-tubulin III, PAX6, neural filament, GFAP and vimentin. Culturing these neural progenitors on confluent ARPE19 monolayer induced expression of the photoreceptor progenitor cell marker CRX; culturing neural progenitors on laminin substrates induced a neuronal phenotype with neurite formation. Neural progenitors expressed the RPE marker ZO-1 after culturing on Matrigel-coated dishes and the RPE marker Bestrophin after culturing on human Bruch's membrane explants. Hierarchical clustering analysis of samples suggested that when cultured on PA6 stromal cells hESC exhibited genetic characteristics towards differentiating into neural retina. Microarray analysis showed that after culturing on PA6 cells, stem cells expressed 117 new genes; among these there were 22 genes present in neural retina or RPE cells. The functions of these genes were highly related to cell proliferation, nervous system development and cell adhesion. HESC can be induced to differentiate into neural progenitors after culturing on PA6 cells. These neural progenitors can express RPE markers when cultured on Bruch's membrane or Matrigel, or photoreceptor markers when cultured on confluent ARPE19 or laminin. Additional studies are required to assess the function of hESC induced to express retinal or RPE markers prior to successful intraocular transplantation into animal models of retinal degeneration.

Cell-based therapy for retina degeneration: the promise of a cure

Cell-based therapies in the retina have been associated with the recovery of visual function in animal models of retinal degeneration. This review covers the current status of such therapies with regard to the source of the donor cells, their integration, and their impact on the degenerating host retina. Emphasis is also put on the importance of a careful interpretation of what is meant by "recovery of visual function". Two main approaches are considered here: (1) the use of human embryonic stem cell derived retinal pigment epithelial (RPE) cells to rescue photoreceptors in an animal model of RPE defect; and (2) the use of photoreceptor precursors to repair the degenerating neural retina. The current conclusions are that major hurdles have to be dealt with, such as finding an appropriate and ethically compliant donor cell source that would yield protracted survival and integration of the replacement retinal cells, and that there is no evidence yet that cell-based therapies can allow the long-term preservation or recovery of conscious vision.

Reduction of iatrogenic RPE lesions in AMD patients: evidence for wound healing?

PURPOSE

Our purpose was to study retinal pigment epithelium (RPE) wound healing in patients with age-related macular degeneration (AMD).

PATIENTS AND METHODS

Abrasive debridement of nasal RPE was performed with a metal cannula during pars plana vitrectomy for foveal choroidal neovascularization (CNV) membrane excision combined with simultaneous autologous RPE transplantation. Fundus autofluorescence, fluorescein angiography images, and red-free pictures were taken initially within 1-2 weeks postoperatively, subsequently in 2-week intervals until 3 months, monthly until 6 months, and every 3 months thereafter. The borders of these lesions were measured; areas were calculated and compared using ArchiCad Software. Fourteen eyes of 14 patients suffering from AMD were included (nine women and four men, mean age 75.6 years +/-6.6 years).

RESULTS

Six of 14 (42.9 %) patients showed a reduction of the RPE debrided area. The size of these lesions reduced 5.6-20% within 2 postoperative months compared with their size at first examination (from a mean of 13.7 mm2 +/- 7.2 at baseline to a mean of 12.8 mm2 +/- 6.7 at 2 months postoperatively). No further reduction of the lesions was seen after the 2 months. In eight cases, borders of the RPE debrided areas stayed stable during observation time.

CONCLUSIONS

Wound healing of abrasively debrided RPE monolayer defects in patients with AMD occurs to a certain extent in nearly half of the cases. This process seems to stop after 2 months.

RPE transplantation and its role in retinal disease

Retinal pigment epithelial (RPE) transplantation aims to restore the subretinal anatomy and re-establish the critical interaction between the RPE and the photoreceptor, which is fundamental to sight. The field has developed over the past 20 years with advances coming from a large body of animal work and more recently a considerable number of human trials. Enormous progress has been made with the potential for at least partial restoration of visual function in both animal and human clinical work. Diseases that have been treated with RPE transplantation demonstrating partial reversal of vision loss include primary RPE dystrophies such as the merTK dystrophy in the Royal College of Surgeons (RCS) rat and in humans, photoreceptor dystrophies as well as complex retinal diseases such as atrophic and neovascular age-related macular degeneration (AMD). Unfortunately, in the human trials the visual recovery has been limited at best and full visual recovery has not been demonstrated. Autologous full-thickness transplants have been used most commonly and effectively in human disease but the search for a cell source to replace autologous RPE such as embryonic stem cells, marrow-derived stem cells, umbilical cord-derived cells as well as immortalised cell lines continues. The combination of cell transplantation with other modalities of treatment such as gene transfer remains an exciting future prospect. RPE transplantation has already been shown to be capable of restoring the subretinal anatomy and improving photoreceptor function in a variety of retinal diseases. In the near future, refinements of current techniques are likely to allow RPE transplantation to enter the mainstream of retinal therapy at a time when the treatment of previously blinding retinal diseases is finally becoming a reality.

Transplantation of the RPE in AMD

The retinal pigment epithelium (RPE) maintains retinal function as the metabolic gatekeeper between photoreceptors (PRs) and the choriocapillaries. The RPE and Bruch's membrane (BM) suffer cumulative damage over lifetime, which is thought to induce age-related macular degeneration (AMD) in susceptible individuals. Unlike palliative pharmacologic treatments, replacement of the RPE has a curative potential for AMD. This article reviews mechanisms leading to RPE dysfunction in aging and AMD, laboratory studies on RPE transplantation, and surgical techniques used in AMD patients. Future strategies using ex vivo steps prior to transplantation, BM prosthetics, and stem cell applications are discussed. The functional peculiarity of the macular region, epigenetic phenomena leading to an age-related shift in protein expression, along with the accumulation of lipofuscin may affect the metabolism in the central RPE. Thickening of BM with age decreases its hydraulic conductivity. Drusen are deposits of extracellular material and formed in part by activation of the alternative complement pathway in individuals carrying a mutant allele of complement factor H. AMD likely represents an umbrella term for a disease entity with multifactorial etiology and manifestations. Presently, a slow progressing (dry) non-neovascular atrophic form and a rapidly blinding neovascular (wet) form are discerned. No therapy is currently available for the former, while RPE transplantation and promising (albeit non-causal) anti-angiogenic therapies are available for the latter. The potential of RPE transplantation was demonstrated in animal models. Rejection of allogeneic homologous transplants in patients focused further studies on autologous sources. In vitro studies elucidated cell adhesion and wound healing mechanisms on aged human BM. Currently, autologous RPE, harvested from the midperiphery, is being transplanted as a cell suspension or a patch of RPE and choroid in AMD patients. These techniques have been evaluated from several groups. Autologous RPE transplants may have the disadvantage of carrying the same genetic information that may have led to AMD manifestation. An intermittent culturing step would allow for in vitro therapy of the RPE, its rejuvenation and prosthesis of BM to improve the success RPE transplants. Recent advances in stem cell biology when combined with lessons learned from studies of RPE transplantation are intriguing future therapeutic modalities for AMD patients.

A new animal model of choroidal neovascularization

PURPOSE

The purpose of this study was to evaluate the ability of different methods to induce choroidal neovascularization (CNV) in the domestic pig.

METHODS

A total of 26 Danish landrace pigs was used. A sample of 22 eyes in 12 pigs underwent retinal photocoagulation with a xenon lamp, six eyes in four pigs underwent retinal photocoagulation with a diode laser, and mechanical rupture of Bruch's membrane (BM) was induced in 12 pigs following surgical debridement of the retinal pigment epithelium without damage to the neuroretina.

RESULTS

All 12 pigs (100%) in the group with mechanical rupture of BM developed CNV. The induced membranes were morphologically similar to CNV membranes in humans. Induced CNV was found in 13 of 22 (54%) xenon lamp-treated animals and in five of six (83%) diode laser-treated animals. The CNV in these groups was small and the morphology of the induced lesions was dominated by retinal gliosis and retinal neovascularization, probably due to a marked destruction of the neuroretina.

CONCLUSIONS

Surgical debridement of the retinal pigment epithelium followed by mechanical rupture of BM is a reproducible method of producing CNV in the domestic pig, whereas photocoagulation gives rise to glially derived subretinal fibrovascular membranes and primarily retinal neovascularization.

Visual prognosis in patients with traumatic choroidal rupture

BACKGROUND

There is a paucity of work in the literature examining the long-term visual prognosis of patients with choroidal ruptures. We performed a study to get a better assessment of long-term visual recovery in these patients as well as to identify prognostic indicators.

METHODS

We reviewed the charts of 32 patients who experienced traumatic choroidal rupture following blunt ocular trauma. All charts contained International Classification of Diseases code 363.63 (choroidal rupture). For inclusion in the study, the chart had to contain detailed drawings or photographic evidence that could confirm the presence and location (foveal, juxtafoveal or extrafoveal) of the choroidal rupture. In addition, demographic data and visual acuity on follow-up examinations had to be present. The mechanism and location of the injury, initial and final visual acuity, associated ocular findings and length of follow-up were recorded.

RESULTS

Of the 32 eyes 31 had indirect choroidal ruptures and I had a direct rupture. The mean final visual acuity values in the foveal, juxtafoveal and extrafoveal subgroups were 20/68, 20/35 and 20/60 respectively after a mean duration of follow-up of 4.5, 3.5 and 4.4 years respectively. There was no statistically significant difference in mean final visual acuity or mean length of follow-up between the three groups. The eight patients with multiple choroidal ruptures had a mean final vision of 20/31 after a mean follow-up period of 3.8 years. The 24 patients with a single choroidal rupture achieved a mean final vision of 20/47 over a mean duration of follow-up of 4.1 years. There was no difference in final vision or in length of follow-up between the two groups. The six patients under 15 years of age attained a mean final vision of 20/34 over a mean follow-up period of 4.5 years, whereas the adult group achieved a mean final vision of 20/44 over a mean follow-up period of 3.8 years. Again, there was no difference in final vision or in length of follow-up between the two groups.

INTERPRETATION

Traumatic choroidal rupture involving the fovea has been thought to have a poor visual prognosis. Our findings show that eyes with foveal choroidal ruptures may regain good central vision over longer follow-up. Furthermore, multiple choroidal ruptures do not necessarily predict a poor visual outcome. Children with choroidal ruptures attained good final visual outcomes.

Ultrastructural analysis of hydraulic and abrasive retinal pigment epithelial cell debridements

Differential changes in Bruch's membrane, choriocapillaris, retinal pigment epithelium, retina, and tapetum after hydraulic or abrasive debridement of the retinal pigment epithelium in the cat area centralis were documented by fluorescein angiography, histology, and transmission electron microscopy at 1-hour, 1-day, 3-day, 1-week, or 4-week time points. Abrasive debridement is associated with abnormal fluorescein angiography and incomplete ingrowth of retinal pigment epithelial cells. Transmission electron microscopy shows that abrasive debridement inflicts more long-lasting ultrastructural damage to Bruch's membrane, the choriocapillaris, tapetum, and retina than does hydraulic debridement. Because the retinal pigment epithelium can resurface abrasively debrided Bruch's membrane that is disorganized, split, reduplicated, or missing, we cannot correlate the ultrastructural appearance of Bruch's membrane with the likelihood of complete resurfacing of the debrided area. Primary choriocapillary or retinal damage in abrasive debridements may contribute to the poor outcome. Regions of retinal degeneration with no underlying retinal pigment epithelial cell monolayer were significantly larger in abrasive debridements at the 4-week than at the 1-week time point. Reduced resurfacing at the later time point suggests that not all cells resurfacing abrasively debrided areas survived over the longer term. This finding may mean that retinal pigment epithelial cells are not able to resurface completely and permanently areas showing geographic atrophy of the choriocapillaris.

Transplantation of allogenic anterior lens capsule to the subretinal space in pigs

PURPOSE

To investigate the consequences of transplantation of a new basement membrane to the subretinal space (SRS) as a substitution of Bruch's membrane.

METHODS

Porcine anterior lens capsules (ALC) were transplanted to the subretinal space of 20 eyes from 19 young Danish landrace pigs. All pigs underwent a three port localized pars plana vitrectomy. Seventeen eyes received naked ALC. In three experiments the ALC was embedded in gelatine, in order to prevent curling of the ALC. The observation period varied between zero and 49 days. The pigs were examined by ophthalmoscopy and fundus photography. Histopathological examination of enucleated eyes was performed at the end of the experiment.

RESULTS

ALCs transplanted to the subretinal space were well-tolerated and caused no inflammation when Bruch's membrane was left undamaged. After 11 days host RPE and glial cells started to cover the ALC in a competitive fashion. When Bruch's membrane was damaged, ingrowths of choroidal vessels and fibroblasts was prominent. The use of gelatine to flatten the ALC did not prevent curling, and gelatine caused pronounced inflammation.

CONCLUSIONS

It is possible to transplant porcine ALC to the SRS of the pig. ALCs are well-tolerated in the SRS and are covered with well-differentiated monolayers of host RPE-cells, if Bruch's membrane is left intact.

Surgical removal of subfoveal choroidal neovascularization: visual outcome and prognostic value of fluorescein angiography and optical coherence tomography

PURPOSE

To study the functional results of macular surgery and determine pre-operative features associated with better final visual outcome.

METHODS

Forty-two consecutive patients underwent surgical removal of subfoveal choroidal neovascularization (CNV), related to age-related macular degeneration (AMD) in 8 eyes, degenerative myopia in 14 eyes, multifocal choroiditis (MFC) in 10 eyes, idiopathic CNV in 6 eyes and other etiologies in 4 eyes. Mean age was 49 years. Pre-operative visual acuity (VA) was 20/200 or less in 30 eyes (71.4%) and never better than 20/40. Fluorescein angiography was analyzed before and after surgery. Pre-operative optical coherence tomographs (OCT) were studied in a masked fashion. Mean follow-up was 12 months (range 4-48 months).

RESULTS

Final VA was 20/200 or less in 25 eyes (60%). According to the CNV etiology, the percentage were 87.5%, 80%, 57.1% and 20% respectively in eyes with AMD, MFC, high myopia, and idiopathic or other diseases. Post-operative VA improved in 21 eyes (50%) but subsequently declined in 7% by the final examination. Patients younger than 50 years had better functional results (p=0.006). Lack of retinal pigment epithelium (RPE) changes on pre-operative angiography was correlated with good visual outcome (p<0.001). The OCT study confirmed some features already described and showed some different CNVpatterns: above and usually separated from the RPE, below and not separated from the RPE, and ungradable. Eyes with the first OCT pattern had the best visual outcome. Main complications included 4 (10%) retinal detachments and 9 (21%) recurrences. OCT was also useful to confirm CNV recurrences post-operatively.

CONCLUSIONS

CNV surgical excision results vary depending on the underlying disease, the RPE and choriocapillaris function, and the features observed on pre-operative OCT images.

Retinal pigment epithelial cell transplantation after subfoveal membranectomy in age-related macular degeneration: clinicopathologic correlation

PURPOSE

To report the histopathology after retinal pigment epithelial cell transplantation and subfoveal membranectomy in age-related macular degeneration.

METHODS

An 85-year-old white woman with bilateral choroidal neovascularization underwent subfoveal membranectomy combined with transplantation of a sheet of human adult retinal pigment epithelium (retinal pigment epithelium) under the foveal center in the right eye. The patient was immunosuppressed postoperatively with prednisone, cyclosporine, and azathioprine. The patient died from congestive heart failure 114 days after surgery.

RESULTS

A patch of hyperpigmentation was visible at the transplant site under the foveola after surgery. Mound-like clusters of individual round, large densely pigmented cells were present in the subretinal space and outer retina in this area. There was loss of the photoreceptor outer segments and native retinal pigment epithelium in the center of the transplant bed, with disruption of the outer nuclear layer predominantly over regions of multilayered pigmented cells. Cystic spaces were present in the inner and outer retina. A residual intra-Bruchs membrane component of the original choroidal neovascular complex was present under the transplant site.

CONCLUSIONS

The transplant site contained clusters of round, pigmented cells that did not form a uniform monolayer in most areas. The morphology at the transplant site is consistent with the lack of visual improvement seen after surgery in this patient.

The role of submacular surgery in the treatment of choroidal neovascular membranes

The growth of choroidal neovascular membranes (CNVM) beneath the macula can cause significant disturbances of central vision. Conditions such as age-related macular degeneration (AMD) and presumed ocular histoplasmosis syndrome (POHS) are the most common etiologies. The Macular Photocoagulation Study group presented data that clearly showed laser photocoagulation to be beneficial in the treatment of CNVM. Poor visual results and a high rate of recurrence have prompted clinicians to seek out alternative treatments. Experiences with CNVM removal utilizing submacular surgical techniques have shown that central visual function may be restored or preserved in POHS, multifocal choroiditis and idiopathic causes. The Submacular Surgery Trials were designed to investigate whether submacular surgery is more effective in retaining central acuity in patients with subfoveal CNVM, than observation alone. The goal of this paper is to review the role of submacular surgery in the treatment of subfoveal choroidal neovascular membranes.

Verteporfin photodynamic therapy retreatment of normal retina and choroid in the cynomolgus monkey

OBJECTIVE

This study evaluated the effect of repeated photodynamic therapy (PDT) applications on normal primate retina and choroid using an intravenous infusion of liposomal benzoporphyrin derivative (verteporfin).

DESIGN

This was an experimental study in a primate model. ANIMALS/CONTROLS: Six cynomolgus monkeys were used as experimental subjects and one monkey was used as a control subject.

INTERVENTION

Three consecutive PDT treatments at 2-week intervals were applied over the center of the fovea or the optic nerve of each eye. Verteporfin was delivered by intravenous infusion at a dose of 6 mg/m2, 12 mg/m2, or 18 mg/m2. Laser irradiation was then applied using a diode laser (689 nm) with light doses and spot sizes kept constant.

MAIN OUTCOME MEASURES

Findings were documented by fundus photography, fluorescein angiography, and light and electron microscopy.

RESULTS

A cumulative dose response was seen angiographically and histologically with more severe damage to the retina and choroid noted at higher dye doses. Photodynamic therapy applied to the macula using the 6-mg/m2 verteporfin dose showed recovery of choriocapillaris, with mild retinal pigment epithelium and outer photoreceptor damage at 6 weeks. At this dose, the optic nerve showed few focal sites of axon atrophy and capillary loss. Treatments over the macula using the 12-mg/m2 and 18-mg/m2 doses led to chronic absence of choriocapillaris and photoreceptors at 6 weeks. One of two optic nerves became atrophic after PDT applications using dye doses of 12 mg/m2, and both optic nerves became atrophic in the 18-mg/m2 dye dose group.

CONCLUSION

Limited damage to the retina, choroid, and optic nerve was present in primates treated with multiple PDT sessions using 6 mg/m2 verteporfin with light doses and the timing of irradiation kept constant. However, PDT using higher dye doses of 12 mg/m2 and 18 mg/m2 led to significant chronic damage to the normal retina, choroid, and optic nerve.

Transplanted and repopulated retinal pigment epithelial cells on damaged Bruch's membrane in rabbits

AIMS

The authors studied how artificially damaged Bruch's membrane influenced growth and differentiation of transplanted embryonic retinal pigment epithelial (RPE) cells and of host RPE cells in rabbits.

METHODS

Embryonic RPE cells obtained from pigmented rabbits were transplanted into the subretinal space of adult albino rabbits. The host RPE was removed with a silicone cannula, and Bruch's membrane was damaged by scratching with a microhooked 27 gauge needle under the detached retina in closed vitrectomy. The transplantation sites were examined 3, 7, and 14 days after surgery by light and electron microscopy.

RESULTS

Varying degrees of damage in Bruch's membrane were observed. Pigmented and hypopigmented RPE cells showed a normal polarity and tight junctions were seen at the sites of mild to moderate damage 3-7 days after the surgery. In contrast, fibroblast-like cells with no such features of RPE cells formed multiple layers at the sites of severe damage involving the full thickness of Bruch's membrane and the choriocapillaris even 14 days after the surgery. Without transplantation, host RPE cells repopulated the damaged areas in the same way as transplanted RPE cells.

CONCLUSIONS

Transplanted embryonic RPE cells as well as host RPE cells grew and differentiated on the moderately damaged Bruch's membrane, while the severely damaged Bruch's membrane did not allow differentiation of RPE cells although these cells could grow and cover the damaged areas.

Analysis of extracellular matrix synthesis during wound healing of retinal pigment epithelial cells

To investigate changes in retinal pigment epithelial (RPE) cells during wound healing, we evaluated the deposition of newly synthesized extracellular matrix (ECM) over time during wound healing in rat RPE cultures. We also estimated the effect of growth factors on the healing rate and ECM synthesis. After preparing rat RPE cell sheet cultures, we made round 1-mm defects in the cultures. Fibronectin, laminin, and collagen IV synthesis were evaluated with immunocytochemistry every 12 hours after wounding. S-phase cell distribution was analyzed every 12 hours by 5-bromodeoxyuridine uptake. We added either platelet-derived growth factor (PDGF), epidermal growth factor (EGF), or transforming growth factor- beta2 (TGF-beta2) to cultures at concentrations of 1, 10, and 100 ng/mL and immunocytochemically analyzed the effects on ECM and estimated the rate of wound closure. Although approximately 50% closure was achieved 24 hours after wounding, fibronectin deposits first appeared at that time. Laminin and collagen IV were first detected at 36 hours and fibronectin staining had extended toward the wound center. S-phase cells were distributed in concentric rings that moved centripetally over time and corresponded to the leading edge of the area stained with anti-ECM antibodies. TGF-beta2 enhanced ECM deposition, but EGF and PDGF did not. TGF-beta2 decreased the healing rate in a dose-dependent manner, whereas PDGF promoted wound closure. EGF enhanced closure at the highest concentration only. In summary, wound healing in RPE may be initiated when cells at the wound edge slide or migrate toward the wound center, which is followed by cell proliferation and then ECM synthesis. ECM components may be produced in a specific sequence during healing. TGF-beta2 may promote RPE cell differentiation, and PDGF may enhance proliferation during wound healing of the RPE.

Scanning and transmission electron microscopic findings during RPE wound healing in vivo

OBJECTIVE

To examine the scanning (SEM) and transmission (TEM) electron microscopic features of an in vivo rabbit model of retinal pigment epithelial (RPE) wound healing.

METHODS

Hydraulic debridement of the RPE was performed in one eye of each of 35 pigmented rabbits using a pars plana vitrectomy approach. Five of the 35 eyes were examined by either SEM or TEM on each of the following postoperative days: 0, 2, 4, 7, 14, 28 and 56.

RESULTS

TEM revealed that hydraulic RPE debridement results in only focal damage to the RPE basement membrane portion of Bruch's membrane and that this damage is repaired by day 7 without ultrastructural sequelae. SEM and TEM disclosed that the RPE cells at the margin of the debrided bed become flattened and enlarged and evolve a cytoskeletal reorganization with altered apical-basal polarity consistent with the development of a migrating phenotype. This is followed by gradual restoration to a more normal stationary RPE phenotype after initial closure (reepithelialization) of the RPE defect on day 7. RPE hyperplasia also occurs and may contribute to this repair process. Tight junctions are re-established among the apical surfaces of monolayered and multilayered RPE cells by day 7, coinciding with the restoration of the blood outer retinal barrier.

CONCLUSION

Hydraulic debridement of the RPE in vivo is a useful investigational model that provides important insight into the pathogenesis of outer retinal disorders and their treatment with such techniques as submacular surgery or RPE transplantation.

Scanning laser ophthalmoscope fundus perimetry after surgery for choroidal neovascularization

PURPOSE

Submacular surgery is under investigation for the treatment of subfoveal choroidal neovascularization secondary to age-related macular degeneration, ocular histoplasmosis syndrome, and other causes. The aims of this study were to determine whether the macular area from which choroidal neovascularization was removed surgically remained functional and whether there was any qualitative difference between eyes with different disease conditions or between eyes of younger and older patients.

METHODS

Our study included 19 patients (19 eyes) with choroidal neovascularization, seven cases caused by age-related macular degeneration and 12 caused by ocular histoplasmosis syndrome, pathologic myopia, or idiopathic causes. All tests were performed at least 6 months after surgical removal of choroidal neovascularization. All patients underwent fundus perimetry with the scanning laser ophthalmoscope for evaluation of dense and relative scotomas and fixation site.

RESULTS

After submacular surgery in 19 patients, 10 patients (one with age-related macular degeneration and nine with pathologic myopia, ocular histoplasmosis syndrome, or an idiopathic cause of choroidal neovascularization) fixated within an area that ophthalmoscopically and angiographically was an area of retinal pigment epithelial disturbance occupied by choroidal neovascularization preoperatively. Of 12 patients without age-related macular degeneration, seven of eight patients younger than 50 years of age compared with two of four patients 50 years or older fixated within the area of retinal pigment epithelial disturbance.

CONCLUSIONS

Our data suggest that in patients without age-related macular degeneration who undergo submacular surgery, the surgically disturbed area previously occupied by choroidal neovascularization can remain functional postoperatively. Furthermore, occasionally a patient with age-related macular degeneration undergoing submacular surgery still can fixate in the area from which the choroidal neovascularization was removed.

In vitro transplantation of fetal human retinal pigment epithelial cells onto human cadaver Bruch's membrane

Retinal pigment epithelium transplantation has been proposed as adjunctive treatment for age-related macular degeneration following surgical excision of choroidal neovascular membranes. The goal of this study was to develop a model to evaluate retinal pigment epithelium transplantation onto human Bruch's membrane in vitro. We investigated the ability of cultured fetal human retinal pigment epithelium to colonize human cadaver Bruch's membrane, determined the incubation time needed to form a monolayer and to exhibit apical microvilli and tight junctions, and assessed the production of basement membrane. Freshly enucleated (less than 48 hours old) human eyes were cut through the pars plana, and the anterior segment, vitreous, and retina were removed. The native retinal pigment epithelium was debrided with a surgical sponge. Bruch's membrane and choroid at the macula were trephined with a 7.0 mm diameter trephine and then incubated with 1/2 ml of Dulbecco's modified Eagle's medium +15% fetal calf serum+basic fibroblast growth factor (1 ng ml-1), and fetal human retinal pigment epithelium at a concentration of 242,000 cells ml-1. Specimens were incubated for 1, 4, 6, 8, 12, or 24 hours. The specimens were fixed in half strength Karnovsky's fixative, processed, and analysed with scanning and transmission electron microscopy. The retinal pigment epithelium covered the debrided macular specimens to different degrees at different incubation times. After 1 hour, the cells started to attach and flatten (median percent coverage: 78%). The extent of Bruch's membrane coverage by fetal retinal pigment epithelium varied greatly between specimens. After 4-6 hours, the cells covered the entire debrided surface in a monolayer (median percent coverage: 97.2% at 4 hours, 99.8% at 6 hours). Tight junctions were observed, and the cells had few apical microvilli. The lateral cell borders were obliquely oriented with respect to Bruch's membrane, and the nuclei were elongated, exhibited prominent nucleoli, and were oriented parallel to Bruch's membrane. After 6-8 hours, cells started to become hexagonal (median percent coverage at 8 hours: 99.97%). Cells attached to the inner collagenous layer tended to be flatter than cells attached to residual native basement membrane. At 12 and 24 hours, expression of hexagonal shape, tight junctions, and apical microvilli were observed more frequently (median percent coverage: 99.87% at 12 and 100% at 24 hours). No newly formed basement membrane was observed at these time points. In separate experiments comparing attachment in the presence and absence of native RPE basement membrane, the presence of native retinal pigment epithelial basement membrane promoted the early attachment of the cells and more rapid expression of normal morphology. This in vitro system provides a reproducible way to study the adherence of retinal pigment epithelium to normal and diseased human Bruch's membrane.

Transplantation of retinal pigment epithelium using viable cryopreserved cells

Transplantation of retinal pigment epithelium (RPE) may have potential clinical application for the surgical treatment of RPE-specific retinal degeneration, including age-related macular degeneration. The feasibility of an RPE storage bank has been investigated by experimenting with transplantation using viable, cryopreserved RPE cells. Fresh and cultured fetal human and bovine RPE cells were cryopreserved in 90% fetal bovine serum containing 10% dimethyl sulfoxide. The viability of the cells before and after cryopreservation was evaluated by trypan blue dye exclusion test, microculture tetrazolium assay (MTA), tissue culture, and transplantation after cryopreservation. The origin of RPE cells before and after cryopreservation was assessed by immunocytochemistry, immunoblotting, and indirect ELISA of RPE-marker protein using cytokeratin for cultured fetal human RPE cells and by immunocytochemistry of cellular retinaldehyde-binding protein (CR-ALBP) for cultured bovine RPE cells. Freshly isolated and cryopreserved uncultured bovine RPE cells were transplanted by posterior transscleral approach into the subretinal spaces of adult albino rabbits and 23-day-old Royal College of Surgeons (RCS) rats with a 33 gauge Hamilton syringe. Following surgery, artificial retinal blebs were confirmed by fundus examination. Morphologic examination was performed postoperatively by light and electron microscopy in albino rabbits and by light microscopy in RCS rats up to 3 mo. Control subretinal injections using vehicle solution also were performed in RCS rats. Cultured fetal human and bovine RPE cells after cryopreservation were found to be viable, based on the results of trypan blue dye exclusion test, MTA, tissue culture, and transplantation. Expression and reexpression of cytokeratin intermediate filaments in cultured fetal human RPE were demonstrated by immunocytochemistry, immunoblotting, and indirect ELISA before and after cryopreservation. Immunocytochemistry of CRALBP before and after cryopreservation in uncultured bovine RPE cells disclosed expression and reexpression of RPE cell marker protein. No uncultured fetal human RPE cells showed proliferation in tissue culture after cryopreservation. In rabbits, light and electron microscopy disclosed xenografted RPE cells residing on Bruch's membrane of the host retina. No sign of graft vs. host reaction was observed. No morphologic difference was noted between the fresh and 10-day-old cryopreserved RPE cells in situ following transplantation at day 25. In RCS rats, subretinal injection of 3-wk-old cryopreserved bovine RPE cells partially rescued photoreceptor cells locally at the transplanted area observed at 3 mo postoperatively. The retinal photoreceptors at the inferior hemisphere of the transplanted eye and the eye injected with vehicle solution showed no rescue effect. We found that cryopreserved cultured fetal human RPE cells and uncultured and cultured bovine RPE cells can be used for RPE transplantation studies. The ability to create an RPE storage bank as a source of donor cells may result in several clinical advantages.

Transplantation of RPE in age-related macular degeneration: observations in disciform lesions and dry RPE atrophy

A study was carried out to investigate whether human RPE allografts are tolerated or rejected in the subretinal space and to determine the feasibility of RPE transplantation in subjects with age-related macular degeneration (AMD).

METHODS

Patches of human fetal RPE (13-20 weeks of gestational age) were transplanted into the subretinal space of five patients after surgical removal of subfoveal fibrovascular membranes, and to four subjects with dry geographic atrophy. Suspensions of RPE cells were transplanted to four other patients with nonexudative AMD. Results were evaluated with clinical ophthalmological examination, SLO microperimetry and fluorescein angiography over 8-20 months.

RESULTS

In disciform lesions, RPE transplants developed macular edema and fluorescein leakage concomitant with gradual reduction of visual acuity, implying host-graft rejection, over 1-6 months. In geographic atrophy, three of four transplants showed little change in shape and size after 12 months (one transplant was slowly rejected). In non-exudative AMD, RPE suspension transplants showed no evidence of rejection and were associated with the disappearance of drusen; visual acuity remained stable and SLO microperimetry confirmed retinal function over the transplanted area.

CONCLUSION

Human RPE allografts are not invariably rejected in the subretinal space without immunosuppression. The rejection rate is lower in nonexudative than in neovascular AMD. An intact blood-retinal barrier is likely to protect against rejection. It is technically feasible to transplant human RPE into the submacular space without adversely affecting visual function in nonexudative AMD over relatively long periods of time.

Perfusion of the subfoveal choriocapillaris affects visual recovery after submacular surgery in presumed ocular histoplasmosis syndrome

PURPOSE

To determine the relationship between the visual result and perfusion of the subfoveal choriocapillaris after surgical excision of subfoveal neovascularization in presumed ocular histoplasmosis syndrome.

METHODS

We reviewed the records of 38 eyes of 37 patients with gradable postoperative fluorescein angiograms and color photographs after surgical excision of a subfoveal neovascular membrane in presumed ocular histoplasmosis syndrome. The postoperative photographs and fluorescein angiograms were graded in a masked fashion for the presence of perfusion of the subfoveal choriocapillaris. We used preoperative and postoperative best-corrected visual acuities to determine the correlation between postoperative perfusion of the subfoveal choriocapillaris and both final visual acuity and visual improvement after surgery.

RESULTS

After surgery, the subfoveal choriocapillaris was perfused in 24 of the 38 eyes (63%) and nonperfused in 14 (37%). Best-corrected visual acuity improved by at least 2 Snellen lines in 17 of the 24 perfused eyes (71%) and two of the 14 nonperfused eyes (14%) (P = .0089). Best-corrected visual acuity of 20/100 or better was achieved in 18 of the perfused eyes (75%) and four nonperfused eyes (29%) (P = .0076).

CONCLUSION

Both final visual acuity and improvement in visual acuity were correlated with postoperative perfusion of the subfoveal choriocapillaris in patients with presumed occular histoplasmosis syndrome. Development of techniques to maintain or reestablish perfusion of the subfoveal choriocapillaris after surgery may improve visual outcome in these eyes.

Correlation between scanning laser ophthalmoscope microperimetry and anatomic abnormalities in patients with subfoveal neovascularization

PURPOSE

The purpose of the study is to identify the anatomic abnormalities associated with an absolute scotoma and the location and stability of fixation in patients with subfoveal neovascularization in age-related macular degeneration, presumed ocular histoplasmosis syndrome, and other disorders.

METHODS

Scanning laser ophthalmoscope microperimetry was superimposed on color fundus photographs and fluorescein angiograms of 21 eyes with subfoveal neovascular membranes secondary to age-related macular degeneration (14 eyes) and presumed ocular histoplasmosis syndrome (7 eyes). The authors determined the location and the area occupied by the absolute scotoma and each of the following subretinal lesions: subretinal hemorrhage, neurosensory retinal detachment, retinal pigment epithelial (RPE) atrophy, RPE hyperplasia, atrophy of the choriocapillaris, hard exudates, and the subfoveal neovascular membrane. The area of absolute scotoma determined by scanning laser ophthalmoscope microperimetry was superimposed on the anatomic lesions. The authors calculated the relative risk ratio (RR) of an absolute scotoma occurring in regions corresponding to each anatomic abnormality, and determined the preferred location and stability of fixation in each eye.

RESULTS

An absolute scotoma was present in areas of chorioretinal scar (RR = 107.61), RPE atrophy (RR = 9.97), subretinal hemorrhage (RR = 2.88), and the neovascular membrane (RR = 1.86). Fixation was stable in all patients with presumed ocular histoplasmosis syndrome but only 29% of patients with age-related macular degeneration. Fifty-five percent of patients with stable fixation fixated over an area of RPE hyperplasia.

CONCLUSION

The relative risk of an absolute scotoma is highest over areas of chorioretinal scars, RPE atrophy, subretinal hemorrhage, and the neovascular membrane. Fixation is more stable in patients with subfoveal neovascularization from presumed ocular histoplasmosis syndrome than with age-related macular degeneration and frequently is present over an area of RPE hyperplasia.

Retinal pigment epithelial debridement as a model for the pathogenesis and treatment of macular degeneration

PURPOSE

To determine the effects of the absence of the retinal pigment epithelium on the choriocapillaris and outer retina by performing retinal pigment epithelial cell debridement with mitomycin C to inhibit cell proliferation pharmacologically in the porcine eye.

METHODS

A pars plana vitrectomy was performed in 12 eyes, and two neurosensory retinal detachments per eye were created by injecting 10(-3) mg/ml mitomycin C and 0.25% edetic acid into the subretinal space. Twenty minutes later, the retinal pigment epithelium was debrided, and the retina was reattached with a fluid-gas exchange.

RESULTS

Bruch's membrane was devoid of native retinal pigment epithelium, and the choriocapillaris was patent immediately after debridement. No proliferation of the retinal pigment epithelium occurred 1 week after debridement, and choriocapillaris atrophy was present beneath areas of Bruch's membrane that were devoid of retinal pigment epithelium. Four weeks postsurgery, choriocapillaris atrophy persisted in all debrided blebs, although unpigmented retinal pigment epithelium repopulated portions of Bruch's membrane in one of three blebs. Outer retinal atrophy was present in areas of Bruch's membrane with no retinal pigment epithelium and no choriocapillaris 4 weeks postsurgery. The choriocapillaris was patent in areas of mitomycin C injection without debridement.

CONCLUSION

Absence of the retinal pigment epithelium leads to atrophy of the choriocapillaris within 1 week after surgery. This finding provides an animal model to study transplantation of retinal pigment epithelium onto bare patches of Bruch's membrane in age-related macular degeneration and other diseases and provides insight into the pathogenesis of nonexudative age-related macular degeneration.

Postoperative abnormalities of the choriocapillaris in exudative age-related macular degeneration

AIMS

To study the incidence and possible cause of abnormalities of the subfoveal choriocapillaris after surgical excision of subfoveal choroidal neovascularisation in age-related macular degeneration (ARMD).

METHODS

The postoperative fluorescein angiograms and colour photographs of 29 eyes of 29 patients were reviewed after surgical excision of subfoveal choroidal neovascularisation in exudative ARMD. Preoperative and postoperative fluorescein angiograms were examined for perfusion of the subfoveal choriocapillaris. The excised subfoveal choroidal neovascular membranes from eight eyes that demonstrated postoperative abnormalities of the choriocapillaris were embedded in paraffin, serially sectioned and examined for the presence of the choriocapillaris.

RESULTS

Postoperative fluorescein angiograms revealed abnormal perfusion of the subfoveal choriocapillaris in 26 of the 29 eyes (90%) and in all eight eyes that had histopathological examination of the surgical specimens. Examination of serial sections demonstrated that none of the excised neovascular membranes contained choriocapillaris.

CONCLUSIONS

Abnormal perfusion of the subfoveal choriocapillaris was frequently present following removal of the subfoveal neovascular membrane in ARMD. The histopathological study demonstrated that abnormalities of the choriocapillaris were not due to removal of the choriocapillaris at the time of surgery.