Central Retinal Pigment Epithelium Research Articles

SIRT6 overexpression in the nucleus protects mouse retinal pigment epithelium from oxidative stress.

Retinal pigment epithelium (RPE) is essential for the survival of retinal photoreceptors. To study retinal degeneration, sodium iodate (NaIO3) has been used to cause oxidative stress-induced RPE death followed by photoreceptor degeneration. However, analyses of RPE damage itself are still limited. Here, we characterized NaIO3-induced RPE damage, which was divided into three regions: periphery with normal-shaped RPE, transitional zone with elongated cells, and center with severely damaged or lost RPE. Elongated cells in the transitional zone exhibited molecular characteristics of epithelial-mesenchymal transition. Central RPE was more susceptible to stresses than peripheral RPE. Under stresses, SIRT6, an NAD+-dependent protein deacylase, rapidly translocated from the nucleus to the cytoplasm and colocalized with stress granule factor G3BP1, leading to nuclear SIRT6 depletion. To overcome this SIRT6 depletion, SIRT6 overexpression was induced in the nucleus in transgenic mice, which protected RPE from NaIO3 and partially preserved catalase expression. These results demonstrate topological differences of mouse RPE and warrant further exploring SIRT6 as a potential target for protecting RPE from oxidative stress-induced damage.

Vitrectomy for Subretinal and Submacular Hemorrhages

Submacular hemorrhage (SMH) is relatively rare in retinal practice. However, it is an important complication of many choroidal and retinal diseases, particularly neovascular age-related macular degeneration (AMD). When untreated the visual prognosis is poor, especially in patients with AMD, and SMHs cannot be effectively treated with only anti-vascular endothelial growth factor (anti-VEGF) injection. The current therapeutic approach is based upon the displacement of the subretinal hemorrhage away from the central retina as soon as possible. The use of tissue plasminogen activator (tPA) has been an important milestone in the treatment of SMHs. Current vitrectomy techniques for SMH management include subretinal tPA injection and aspiration of the blood, and subretinal tPA, and air/anti-VEGF injection with gas tamponade. Submacular surgery, which involves removal of the SMH and choroidal neovascularization (CNV) through a retinotomy, seems to be a technique reserved for selected cases where central retinal pigment epithelium appears to be undiseased/uninvolved. Among the non-surgical treatment options, pneumatic displacement with intravitreal tPA and gas injection may be preferred especially for small-medium sized and thin SMHs. However, the favored approach in real-life conditions is shaped by the physician's experience and the available treatment options. Regardless of the preferred approach, the continuity of the treatment of the underlying pathology is important. As the underlying pathology is usually a CNV, the continuation of anti-VEGF treatment is important for maintaining the visual gain of the initial treatment and reducing the risk of recurrent SMH. The breakthrough development rate of the drugs and the surgical techniques for the treatment of retinal diseases promises in terms of new and more effective treatment approaches.

Factors affecting the response to subthreshold micropulse laser therapy used in center-involved diabetic macular edema.

The purpose of this study was to investigate the effect of the status of retinal pigment epithelium (RPE) and HbA1c levels on the efficacy of the subthreshold micropulse laser (SMPL) in the treatment of center-involving diabetic macular edema (DME). A total of 20 eyes of 20 patients (mean age 57.9 ± 9.7years) who were diagnosed with center-involving DME and treated with SMPL for refusing intravitreal injection and 20 eyes of 20 age- and sex-matched healthy participants were enrolled. All patients were followed up in the 1st and 3rd months after SMPL. For measurement of RPE area central 1000 microns, macular EDI-OCT scans were binarized by using the public domain software ImageJ, with a semi-automated technique. There was a significant increase in BCVA values and a significant decrease in CMT values during follow-up. The area of RPE before SMPL was significantly thinner in the patient group (p: 0.004). When the areas of RPE before and 3months after SMPL were compared, no significant change was observed (p: 0.437). When the relationship between pre-treatment area of RPE and HbA1c was examined, an inverse correlation was observed (p: 0.018). The patients were evaluated by dividing them into 2 groups as 2nd session SMPL required and not required, and the area of RPE was smaller in the group requiring 2nd session SMPL (p: 0.030). The status of central RPE may be a determining factor on the response to treatment. Additionally, HbA1c levels may have an impact on treatment efficacy.

Clinical Manifestations of Cuticular Drusen: Current Perspectives.

Cuticular drusen are part of the spectrum of age-related macular degeneration (AMD) with particular clinical and multimodal imaging characteristics. This drusen subpopulation shares several high-risk single nucleotide polymorphisms with AMD. Despite this feature, they can manifest at a relatively young age, presenting with a female preponderance. Multimodal imaging is essential for characterizing such lesions, using a combination of color fundus photographs, optical coherence tomography (OCT), fluorescein angiography (FA), and fundus autofluorescence (FAF). The classic starry-sky pattern visible on FA and the typical central hypoautofluorescent lesion with hyperautofluorescent rim on FAF is considered the result of a central retinal pigment epithelium (RPE) erosion from these triangular elevations of the RPE-basal lamina. This finding may also be responsible for the typical choroidal hypertransmission appreciated through OCT. The clinical course of cuticular drusen may be relatively benign at early stages, with small drusen presenting at a young age. However, the presence of clinical phenotypes characterized by diffuse involvement and/or accompanying large drusen in patients older than 60 years may confer a significant risk for either macular neovascularization or geographic atrophy.

Electrophysiologic and Morphologic Strain Differences in a Low-Dose NaIO3-Induced Retinal Pigment Epithelium Damage Model.

PurposeWe aimed to explore differences in the NaIO3-elicited responses of retinal pigment epithelium (RPE) and other retinal cells associated with mouse strains and dosing regimens.MethodsOne dose of NaIO3 at 10 or 15 mg/kg was given intravenously to adult male C57BL/6J and 129/SV-E mice. Control animals were injected with PBS. Morphologic and functional changes were characterized by spectral domain optical coherence tomography, electroretinography, histologic, and immunofluorescence techniques.ResultsInjection with 10 mg/kg of NaIO3 did not cause consistent RPE or retinal changes in either strain. Administration of 15 mg/kg of NaIO3 initially induced a large transient increase in scotopic electroretinography a-, b-, and c-wave amplitudes within 12 hours of injection, followed by progressive structural and functional degradation at 3 days after injection in C57BL/6J mice and at 1 week after injection in 129/SV-E mice. RPE cell loss occurred in a large posterior-central lesion with a ring-like transition zone of abnormally shaped cells starting 12 hours after NaIO3 treatment.ConclusionsNaIO3 effects depended on the timing, dosage, and mouse strain. The RPE in the periphery was spared from damage compared with the central RPE. The large transient increase in the electroretinography was remarkable.Translational RelevanceThis study is a phase T1 translational research study focusing on the development and validation of a mouse model of RPE damage. It provides a detailed foundation for future research, informing choices of mouse strain, dosage, and time points to establish NaIO3-induced RPE damage.

Progression of Retinopathy Secondary to Maternally Inherited Diabetes and Deafness – Evaluation of Predicting Parameters

To investigate the prognostic value of demographic, functional, and imaging parameters on retinal pigment epithelium (RPE) atrophy progression secondary to maternally inherited diabetes and deafness (MIDD) and to evaluate the application of these factors in clinical trial design. Retrospective observational case series. Thirty-five eyes of 20 patients (age range, 24.9-75.9 years) with genetically proven MIDD and demarcated RPE atrophy on serial fundus autofluorescence (AF) images were included. Lesion size and shape-descriptive parameters were longitudinally determined by 2 independent readers. A linear mixed-effect model was used to predict the lesion enlargement rate based on baseline variables. Sample size calculations were performed to model the power in a simulated interventional study. The mean follow-up time was 4.27 years. The mean progression rate of RPE atrophy was 2.33mm2/year, revealing a dependence on baseline lesion size (+0.04 [0.02-0.07] mm2/year/mm2, P < .001), which was absent after square root transformation. The fovea was preserved in the majority of patients during the observation time. In the case of foveal involvement, the loss of visual acuity lagged behind central RPE atrophy in AF images. Sex, age, and number of atrophic foci predicted future progression rates with a cross-validated mean absolute error of 0.13mm/year and to reduce the required sample size for simulated interventional trials. Progressive RPE atrophy could be traced in all eyes using AF imaging. Shape-descriptive factors and patients' baseline characteristics had significant prognostic value, guiding appropriate subject selection and sample size in future interventional trial design.

The Expression of Decidual Protein Induced by Progesterone (DEPP) Is Controlled by Three Distal Consensus Hypoxia Responsive Element (HRE) in Hypoxic Retinal Epithelial Cells

Hypoxia affects the development and/or progression of several retinopathies. Decidual protein induced by progesterone (DEPP) has been identified as a hypoxia-responsive gene that may be part of cellular pathways such as autophagy and connected to retinal diseases. To increase our understanding of DEPP regulation in the eye, we defined its expression pattern in mouse and human retina and retinal pigment epithelium (RPE). Interestingly, DEPP expression was increased in an age-dependent way in the central human RPE. We showed that DEPP was regulated by hypoxia in the mouse retina and eyecup and that this regulation was controlled by hypoxia-inducible transcription factors 1 and 2 (HIF1 and HIF2). Furthermore, we identified three hypoxia response elements (HREs) about 3.5 kb proximal to the transcriptional start site that were responsible for hypoxic induction of DEPP in a human RPE cell line. Comparative genomics analysis suggested that one of the three HREs resides in a highly conserved genomic region. Collectively, we defined the molecular elements controlling hypoxic induction of DEPP in an RPE cell line, and provided evidence for an enrichment of DEPP in the aged RPE of human donors. This makes DEPP an interesting gene to study with respect to aging and age-related retinal pathologies.

Generation of an inducible RPE-specific Cre transgenic-mouse line.

The retinal pigment epithelium (RPE) is an epithelial monolayer in the back of the vertebrate eye. RPE dysfunction is associated with retinal degeneration and blindness. In order to fully understand how dysregulation affects visual function, RPE-specific gene knockouts are indispensable. Since the currently available RPE-specific Cre recombinases show lack of specificity or poor recombination, we sought to generate an alternative. We generated a tamoxifen-inducible RPE-specific Cre transgenic mouse line under transcriptional control of an RPE-specific Tyrosinase enhancer. We characterized the Cre-mediated recombinant expression by crossing our RPE-Tyrosinase-CreErT2 mouse line with the tdTomato reporter line, Ai14. Detected fluorescence was quantified via high-content image analysis. Recombination was predominantly observed in the RPE and adjacent ciliary body. RPE flatmount preparations revealed a high level of recombination in adult mice (47.25–69.48%). Regional analysis of dorsal, ventral, nasal and temporal areas did not show significant changes in recombination. However, recombination was higher in the central RPE compared to the periphery. Higher levels of Cre-mediated recombinant expression was observed in embryonic RPE (~83%). Compared to other RPE-specific Cre transgenic mouse lines, this newly generated RPE-Tyrosinase-CreErT2 line shows a more uniform and higher level of recombination with the advantage to initiate recombination in both, prenatal and postnatal animals. This line can serve as a valuable tool for researches exploring the role of individual gene functions, in both developing and differentiated RPE.

Delayed atrophy of the retinal pigment epithelium after submacular surgery.

We report a case of delayed atrophy of the retinal pigment epithelium (RPE) eighteen months after apparently successful excision of submacular choroidal new vessels (CNV) in a patient with age-related macular degeneration (AMD). Submacular surgery for CNV was achieved without visible disturbance of the underlying RPE in an 83 year old man diagnosed with AMD. At the time of surgery the CNV displayed clinical features consistent with lying internal to Bruchs membrane (Type 2 configuration). There was no visible RPE defect at the fovea and vision improved during the subsequent 12 months follow-up. Eighteen months later, however, an atrophic central RPE defect appeared, with a similar shape to the CNV originally excised. This case demonstrates that submacular CNV with Type 2 configuration can occur in AMD and lead to an initially favourable outcome following submacular surgery. Atrophy of the RPE nevertheless did eventually occur and in a pattern consistent with damage during the original operation. It is important to consider results of longer term follow-up when interpreting success rates for surgery in AMD. (Eur J Ophthalmol 2005; 15: 170-2).

Observation of curative effect of intravitreal injection of conbercept in wet age-related macular degeneration: Optical coherence tomography analysis after injection.

To observe the clinical efficacy of intravitreal injection of conbercept in the treatment of wet age-related macular degeneration (wAMD), optical coherence tomography (OCT) and the best corrected visual acuity (BCVA) was observed to measure the changes of anatomical changes of central macular thickness (CMT) and the area and volume of retinal pigment epithelium (RPE) uplift. Fifteen patients (15 eyes) with wet AMD were enrolled in this study. All patients underwent intravitreal injection of conbercept of 0.05 mL once. After 1 week, 1 month, and 3 months, OCT and BCVA were used to examine and to compare with the preoperative and postoperative central macular thickness and RPE uplift area. BCVA (median) increased respectively from 0.12 ± 0.13 to 0.21 ± 0.15 at 1 week, to 0.90 ± 0.25 at 1 month, to 0.38 ± 0.17 at 3 months (p < .001). The thickness of central macular decreased from 500 ± 25 μm to 256 ± 19 μm, 221 ± 29 μm, and 215 ± 14 μm, respectively. The normal physiological structure and stratification of the macular area were clear gradually. Conbercept treatment of wet AMD can significantly improve visual acuity, after 1 month up to the plateau, 3 months of continuous drug injection can make the vision maintained at a high stage, and macular retinal normal structural morphology recovery is good, the treatment has no obvious adverse reactions, and with good security.

RPE morphometry in geographic atrophy due to AMD

The geographic atrophy (GA) junctional zone includes changes in retinal pigment epithelium (RPE) and Bruch's membrane complex that are still difficult to interpret even with clinical high-resolution imaging technologies. We measured and evaluated degenerative RPE cell changes in histological sections of GA eyes. In this study seven GA eyes were evaluated by light microscopy. In three eye sections, zones of typical RPE alterations were graded (0= normal; 1= irregular cells but intact layer; 2= rounded, enlarged, and/or heaped cells; 3= migrating cells in retina; 4= RPE absent). In each graded zone, we measured and analyzed A)the total height of the RPE cell layer, B)the height of individual RPE cells and C)the height of basal deposits. From the outer macula towards the central RPE atrophic area the RPE passed almost steadily upward through grades of increased pathology. A)Zone2 exhibited highly variable total RPE height (16.9± 5.6 µm) with hypertrophic and heaped cells next to atrophic ones. In comparison, zone0 and zone1 showed less variability and aregular total RPE height (10.9± 2.6 µm). B)In zone2 the size of altered RPE cells varied widely (12.4± 5.2 µm, min.5.1, max. 27.5). All detected migrating RPE cells were hypertrophic. C)In zone0 basal deposits were found sporadically. With progressing RPE alterations, basal deposits became progressively continuous and thicker and reached aconsiderable height at the atrophic zone (9.5± 4.3 µm). Our measurements confirmed that degenerative RPE phenomena, particularly of degeneration grade2/3 close to the actual RPE atrophy zone, are often large enough to be visualized in detail with already available modern imaging technologies (e. g. SD-OCT).

In situ regeneration of retinal pigment epithelium by gene transfer of E2F2: a potential strategy for treatment of macular degenerations.

The retinal pigment epithelium (RPE) interacts closely with photoreceptors to maintain visual function. In degenerative diseases such as Stargardt disease and age-related macular degeneration, the leading cause of blindness in the developed world, RPE cell loss is followed by photoreceptor cell death. RPE cells can proliferate under certain conditions, suggesting an intrinsic regenerative potential, but so far this has not been utilised therapeutically. Here, we used E2F2 to induce RPE cell replication and thereby regeneration. In both young and old (2 and 18 month) wildtype mice, subretinal injection of non-integrating lentiviral vector expressing E2F2 resulted in 47% of examined RPE cells becoming BrdU positive. E2F2 induced an increase in RPE cell density of 17% compared with control vector-treated and 14% compared with untreated eyes. We also tested this approach in an inducible transgenic mouse model of RPE loss, generated through activation of diphtheria toxin-A gene. E2F2 expression resulted in a 10-fold increase in BrdU uptake and a 34% increase in central RPE cell density. Although in mice this localised rescue is insufficiently large to be demonstrable by electroretinography, a measure of massed retinal function, these results provide proof-of-concept for a strategy to induce in situ regeneration of RPE for the treatment of RPE degeneration.

Atypical retinal pigment epithelial defects with retained photoreceptor layers: a so far disregarded finding in age related macular degeneration

BackgroundTo report patients with age-related macular degeneration and atypical central retinal pigment epithelium (RPE) defects not attributable to geographic atrophy (GA) or RPE-tears with overlying preserved photoreceptor layers.MethodsMultimodal imaging case-series evaluating the course of atypical RPE- defects in patients with AMD using Color fundus images, Optical coherence tomography (OCT), OCT-Angiography, fundus autofluorescence (FAF) and fluorescein-angiography (FA).ResultsTen patients were identified. Three patients had a prior RPE-rip and were excluded. Seven patients with a mean follow-up period of 47 ± 38 months after the occurrence of the RPE-defect were included (age range 71–87 years). Mean distance Best corrected visual acuity (BCVA) at initial presentation was 0.36 ± 0.29logMAR and at last follow-up visit 0.51 ± 0.43logMAR. Patients presented with clinically apparent GA on funduscopy and FAF, but preserved photoreceptor layers on optical coherence tomography (OCT). On FA there was early hyperfluorescence and late pooling visible. Over time, migration of RPE/drusenoid material right above the Bruch’s membrane with concomitant decrease of hypoautofluorescence was detectable in 4 cases. An enlargement of the RPE-defect was apparent in the remaining 3 cases. The majority (n = 4) showed a drusenoid pigment epithelium detachment (PED) preceding the lesion.ConclusionsBeside GA and characteristic RPE-tears, another atypical form of RPE-defect with overlying preserved photoreceptor layers are found in AMD. This so far disregarded subgroup of patients present with reasonable visual function and long-term survival of photoreceptors layers. Repair mechanisms such as ingrowth of RPE/drusenoid material and persistent subretinal fluid (SRF), but also a RPE-independent visual cycle for cone photopigment within the neurosensory retina may contribute to their favorable course.

Gene transfer of E2F2 induces in situ regeneration of retinal pigment epithelium

SummaryThe retinal pigment epithelium (RPE) interacts closely with photoreceptors and is important for maintaining visual function. In degenerative diseases such as age‐related macular degeneration (AMD), the leading cause of blindness in the developed world, RPE cell loss is followed by photoreceptor cell death. RPE cells can proliferate under certain conditions, suggesting an intrinsic regenerative potential, but so far this has not been utilised therapeutically. Here we use E2F2, a potent transcriptional regulator of cell proliferation, to induce RPE regeneration in vitro and in vivo. Gene transfer of E2F2 induced upregulation of Ki67 and uptake of BrdU in growth arrested ARP19 cells in vitro. In both, young and old C57Bl/6 mice, subretinal lentiviral delivery of E2F2 to the RPE caused a 40‐fold ±27.2 increase in E2F2 positive RPE cells that correlated with a 10‐fold ±4.7 increase in BrdU positive cells and a mean increase of RPE cell density. E2F2 also induced BrdU uptake and increased cell density in the central RPE of RPECreER/DTA mice, where pathology, induced by the activation of diphtheria toxin‐A, was strongest. These results provide proof of concept for a strategy to treat progressive RPE cell loss by in situ regeneration.

A2E and Lipofuscin.

Lipofuscin is highly fluorescent material, formed in several tissues but best studied in the eye. The accumulation of lipofuscin in the retinal pigment epithelium (RPE) is a hallmark of aging in the eye and has been implicated in various retinal degenerations, including age-related macular degeneration. The bis-retinoid N-retinyl-N-retinylidene ethanolamine (A2E), formed from retinal, has been identified as a byproduct of the visual cycle, and numerous in vitro studies have found toxicity associated with this compound. The compound is known to accumulate in the RPE with age and was the first identified compound extracted from lipofuscin. Our studies have correlated the distribution of lipofuscin and A2E across the human and mouse RPE. Lipofuscin fluorescence was imaged in the RPE from human donors of various ages and from assorted mouse models. The spatial distribution of A2E was determined using matrix-assisted laser desorption-ionization imaging mass spectrometry on both flat-mounted and transversally sectioned RPE tissue. Our data support the clinical observations in humans of strong RPE fluorescence, increasing with age, in the central area of the RPE. However, there was no correlation between the distribution of A2E and lipofuscin, as the levels of A2E were highest in the far periphery and decreased toward the central region. Interestingly, in all the mouse models, A2E distribution and lipofuscin fluorescence correlate well. These data demonstrate that the accumulation of A2E is not responsible for the increase in lipofuscin fluorescence observed in the central RPE with aging in humans.

Enhanced retinal pigment epithelium regeneration after injury in MRL/MpJ mice

Regenerative medicine holds the promise of restoring cells and tissues that are destroyed in human disease, including degenerative eye disorders. However, development of this approach in the eye has been limited by a lack of animal models that show robust regeneration of ocular tissue. Here, we test whether MRL/MpJ mice, which exhibit enhanced wound healing, can efficiently regenerate the retinal pigment epithelium (RPE) after an injury that mimics the loss of this tissue in age-related macular degeneration. The RPE of MRL/MpJ and control AKR/J mice was injured by retro-orbital injection of sodium iodate at 20 mg/kg body weight, which titration studies indicated was optimal for highlighting strain differences in the response to injury. Five days after sodium iodate injection at this dose, electroretinography of both strains revealed equivalent retinal responses that were significantly reduced compared to untreated mice. At one and two months post-injection, retinal responses were restored in MRL/MpJ but not AKR/J mice. Bright field and fluorescence microscopy of eyecup cryosections indicated an initial central loss of RPE cells and RPE65 immunostaining in MRL/MpJ and AKR/J mice, with preservation of peripheral RPE. Phalloidin staining of posterior eye whole mounts confirmed this pattern of RPE loss, and revealed a transition region characterized by RPE cell shedding and restructuring in both strains, suggesting a similar initial response to injury. At one month post-injection, central RPE cells, RPE65 immunostaining and phalloidin staining were restored in MRL/MpJ but not AKR/J mice. BrdU incorporation was observed throughout the RPE of MRL/MpJ but not AKR/J mice after one month of administration following sodium iodate treatment, consistent with RPE proliferation. These findings provide evidence for a dramatic regeneration of the RPE after injury in MRL/MpJ mice that supports full recovery of retinal function, which has not been observed previously in mammalian eyes. This model should prove useful for understanding molecular mechanisms that underlie regeneration, and for identifying factors that promote RPE regeneration in age-related macular degeneration and related diseases.

Long-term visual outcome of pigment epithelial tears in association with anti-VEGF therapy of pigment epithelial detachment in AMD

Retinal pigment epithelium (RPE) tears may develop as a complication after anti-VEGF (vascular endothelial growth factor) treatment for pigment epithelial detachments (PEDs) in exudative age-related macular degeneration (AMD). This retrospective study analyses best-corrected visual acuity (BCVA) and foveal involvement after RPE tears that are associated with anti-VEGF therapy due to PED in exudative AMD. A total of 37 patients with RPE tears during anti-VEGF therapy (bevacizumab 12, ranibizumab 21 and pegaptanib 4 eyes) for progressive PED in AMD (PED with occult choroidal neovascularization 25 eyes and PED with retinal angiomatous proliferation 12 eyes) were included in this study. We analyzed BCVA and different morphologic aspects by means of appearance on fluorescein angiography and optical coherence tomography. Mean follow-up was 88 weeks. RPE tears were diagnosed a mean of 56 days after the first injection. BCVA deteriorated after RPE tear and during follow-up significantly (P<0.001), with 53.2% of eyes being legally blind (WHO, world health organization) at 12 months. RPE-free foveal area, foveal wrinkling of the RPE, and fibrotic scar development were significantly associated with worse visual acuity. RPE tears can be observed in 12-15% of treated eyes during anti-VEGF therapy for PED in exudative AMD. Owing to the close time relationship with the therapy, this complication must be taken into consideration. Visual prognosis is associated with a decrease in vision in the long term, often resulting in a severe visual disability. Relevant factors for a negative visual prognosis were the potential foveal involvement of the central RPE and morphologic fibrovascular transformation of the RPE tear.

SURGICAL AND ANATOMICAL OUTCOMES OF PARS PLANA VITRECTOMY FOR DIFFUSE NONTRACTIONAL DIABETIC MACULAR EDEMA

To prospectively determine the efficacy of vitrectomy combined with intravitreal triamcinolone acetonide (IVTA) injection, internal limiting membrane (ILM) peeling, or both in treating diffuse nontractional diabetic macular edema (ME). Patients with diffuse ME of <6 months who had no evidence of macular traction or macular ischemia were included in the study. Patients previously diagnosed with glaucoma underwent vitrectomy with ILM peeling. All other patients were randomly assigned to vitrectomy or vitrectomy with ILM peeling followed by IVTA injection. Forty-two eyes of 38 patients were included in the study. Mean follow-up was 12 months. A statistically significant reduction in macular thickness was found at 1 month to 6 months, disappearing at 12 months. No differences in visual acuity between treatment groups were found during follow-up. Visual acuity improved in 5 (12%) of 42 eyes, remained unchanged in 32 (76%) of 42 eyes, and worsened in 5 (12%) of 42 eyes. Complications included increase in intraocular pressure in 8 (26%) of 31 eyes, mild vitreous hemorrhage in 6 (14%) of 42 eyes, central retinal pigment epithelium changes in 5 (12%) of 42 eyes, and cataract progression in 11 (38%) of 29 phakic eyes. In diffuse diabetic ME with no retinal traction, vitrectomy with either ILM peeling or IVTA injection at the end of surgery produces a short-term improvement in retinal thickness but no long-term anatomical or functional improvements.

Human cone photoreceptor dependence on RPE65 isomerase

The visual (retinoid) cycle, the enzymatic pathway that regenerates chromophore after light absorption, is located primarily in the retinal pigment epithelium (RPE) and is essential for rod photoreceptor survival. Whether this pathway also is essential for cone photoreceptor survival is unknown, and there are no data from man or monkey to address this question. The visual cycle is naturally disrupted in humans with Leber congenital amaurosis (LCA), which is caused by mutations in RPE65, the gene that encodes the retinoid isomerase. We investigated such patients over a wide age range (3-52 years) for effects on the cone-rich human fovea. In vivo microscopy of the fovea showed that, even at the youngest ages, patients with RPE65-LCA exhibited cone photoreceptor loss. This loss was incomplete, however, and residual cone photoreceptor structure and function persisted for decades. Basic questions about localization of RPE65 and isomerase activity in the primate eye were addressed by examining normal macaque. RPE65 was definitively localized by immunocytochemistry to the central RPE and, by immunoblotting, appeared to concentrate in the central retina. The central retinal RPE layer also showed a 4-fold higher retinoid isomerase activity than more peripheral RPE. Early cone photoreceptor losses in RPE65-LCA suggest that robust RPE65-based visual chromophore production is important for cones; the residual retained cone structure and function support the speculation that alternative pathways are critical for cone photoreceptor survival.

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.