Age-related alterations in the diffusional transport of amino acids across the human Bruch's-choroid complex

Biomaterial engineering strategies for modeling the Bruch's membrane in age-related macular degeneration

Age-related macular degeneration, a multifactorial inflammatory degenerative retinal disease, ranks as the leading cause of blindness in the elderly. Strikingly, there is a scarcity of curative therapies, especially for the atrophic advanced form of age-related macular degeneration, likely due to the lack of models able to fully recapitulate the native structure of the outer blood retinal barrier, the prime target tissue of age-related macular degeneration. Standard in vitro systems rely on 2D monocultures unable to adequately reproduce the structure and function of the outer blood retinal barrier, integrated by the dynamic interaction of the retinal pigment epithelium, the Bruch's membrane, and the underlying choriocapillaris. The Bruch's membrane provides structural and mechanical support and regulates the molecular trafficking in the outer blood retinal barrier, and therefore adequate Bruch's membrane-mimics are key for the development of physiologically relevant models of the outer blood retinal barrier. In the last years, advances in the field of biomaterial engineering have provided novel approaches to mimic the Bruch's membrane from a variety of materials. This review provides a discussion of the integrated properties and function of outer blood retinal barrier components in healthy and age-related macular degeneration status to understand the requirements to adequately fabricate Bruch's membrane biomimetic systems. Then, we discuss novel materials and techniques to fabricate Bruch's membrane-like scaffolds for age-related macular degeneration in vitro modeling, discussing their advantages and challenges with a special focus on the potential of Bruch's membrane-like mimics based on decellularized tissue.

Progress in Ocular Drug Delivery: Challenges and Constraints

The eye has several dynamic and static barriers in place to limit the entry of foreign substances including therapeutics. As such, efficient drug delivery, especially to posterior segment tissues, has been challenging. This chapter describes the anatomical and physiological challenges associated with ocular drug delivery before discussing constraints with regard to formulation parameters. Finally, it gives an overview of advanced drug delivery technologies with a specific focus on recently marketed and late-stage clinical trial products.

Engineering a Biomimetic In Vitro Model of Bruch's Membrane Using Hagfish Slime Intermediate Filament Proteins

Bruch's membrane resides in the subretinal tissue and regulates the flow of nutrients and waste between the retinal pigment epithelial (RPE) and vascular layers of the eye. With age, Bruch's membrane becomes thicker, stiffer, and less permeable, which impedes its function as a boundary layer in the subretina. These changes contribute to pathologies such as age-related macular degeneration (AMD). To better understand how aging in Bruch's membrane affects surrounding tissues and to determine the relationship between aging and disease, an in vitro model of Bruch's membrane is needed. An accurate model of Bruch's membrane must be a proteinaceous, semipermeable, and nonporous biomaterial with similar mechanical properties to in vivo conditions. Additionally, this model must support RPE cell growth. While models of subretinal tissue exist, they typically differ from in vivo Bruch's membrane in one or more of these properties. This study evaluates the capability of membranes created from recombinant hagfish intermediate filament (rHIF) proteins to accurately replicate Bruch's membrane in an in vitro model of the subretinal tissue. The physical characteristics of these rHIF membranes were evaluated using mechanical testing, permeability assays, brightfield microscopy, and scanning electron microscopy. The capacity of the membranes to support RPE cell culture was determined using brightfield and fluorescent microscopy, as well as immunocytochemical staining. This study demonstrates that rHIF protein membranes are an appropriate biomaterial to accurately mimic both healthy and aged Bruch's membrane for in vitro modeling of the subretinal tissue.

Bruch's Membrane: A Key Consideration with Complement-Based Therapies for Age-Related Macular Degeneration

The complement system is crucial for immune surveillance, providing the body's first line of defence against pathogens. However, an imbalance in its regulators can lead to inappropriate overactivation, resulting in diseases such as age-related macular degeneration (AMD), a leading cause of irreversible blindness globally affecting around 200 million people. Complement activation in AMD is believed to begin in the choriocapillaris, but it also plays a critical role in the subretinal and retinal pigment epithelium (RPE) spaces. Bruch's membrane (BrM) acts as a barrier between the retina/RPE and choroid, hindering complement protein diffusion. This impediment increases with age and AMD, leading to compartmentalisation of complement activation. In this review, we comprehensively examine the structure and function of BrM, including its age-related changes visible through in vivo imaging, and the consequences of complement dysfunction on AMD pathogenesis. We also explore the potential and limitations of various delivery routes (systemic, intravitreal, subretinal, and suprachoroidal) for safe and effective delivery of conventional and gene therapy-based complement inhibitors to treat AMD. Further research is needed to understand the diffusion of complement proteins across BrM and optimise therapeutic delivery to the retina.

The Role of Oxidative Stress in the Aging Eye

Given the expanding elderly population in the United States and the world, it is important to understand the processes underlying both natural and pathological age-related changes in the eye. Both the anterior and posterior segment of the eye undergo changes in biological, chemical, and physical properties driven by oxidative stress. With advancing age, changes in the anterior segment include dermatochalasis, blepharoptosis, thickening of the sclera, loss of corneal endothelial cells, and stiffening of the lens. Changes in the posterior segment include lowered viscoelasticity of the vitreous body, photoreceptor cell loss, and drusen deposition at the macula and fovea. Age-related ocular pathologies including glaucoma, cataracts, and age-related macular degeneration are largely mediated by oxidative stress. The prevalence of these diseases is expected to increase in the coming years, highlighting the need to develop new therapies that address oxidative stress and slow the progression of age-related pathologies.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Variability in Retinal Neuron Populations and Associated Variations in Mass Transport Systems of the Retina in Health and Aging

Aging is associated with a broad range of visual impairments that can have dramatic consequences on the quality of life of those impacted. These changes are driven by a complex series of alterations affecting interactions between multiple cellular and extracellular elements. The resilience of many of these interactions may be key to minimal loss of visual function in aging; yet many of them remain poorly understood. In this review, we focus on the relation between retinal neurons and their respective mass transport systems. These metabolite delivery systems include the retinal vasculature, which lies within the inner portion of the retina, and the choroidal vasculature located externally to the retinal tissue. A framework for investigation is proposed and applied to identify the structures and processes determining retinal mass transport at the cellular and tissue levels. Spatial variability in the structure of the retina and changes observed in aging are then harnessed to explore the relation between variations in neuron populations and those seen among retinal metabolite delivery systems. Existing data demonstrate that the relation between inner retinal neurons and their mass transport systems is different in nature from that observed between the outer retina and choroid. The most prominent structural changes observed across the eye and in aging are seen in Bruch's membrane, which forms a selective barrier to mass transfers at the interface between the choroidal vasculature and the outer retina.

Anatomy and development of the macula: specialisation and the vulnerability to macular degeneration

The central retina in primates is adapted for high acuity vision. The most significant adaptations to neural retina in this respect are: 1. The very high density of cone photoreceptors on the visual axis; 2. The dominance of Midget pathways arising from these cones and 3. The diminishment of retinal blood supply in the macula, and its absence on the visual axis. Restricted blood supply to the part of the retina that has the highest density of neural elements is paradoxical. Inhibition of vascular growth and proliferation is evident during foetal life and results in metabolic stress in ganglion cells and Muller cells, which is resolved during formation of the foveal depression. In this review we argue that at the macula stressed retinal neurons adapt during development to a limited blood supply from the choriocapillaris, which supplies little in excess of metabolic demand of the neural retina under normal conditions. We argue also that while adaptation of the choriocapillaris underlying the foveal region may initially augment the local supply of oxygen and nutrients by diffusion, in the long term these adaptations make the region more vulnerable to age-related changes, including the accumulation of insoluble material in Bruch's membrane and beneath the retinal pigment epithelium. These changes eventually impact on delivery of oxygen and nutrients to the RPE and outer neural retina because of reduced flow in the choriocapillaris and the increasing barriers to effective diffusion. Both the inflammatory response and the sequelae of oxidative stress are predictable outcomes in this scenario.

Retinal pigment epithelium transcriptome analysis in chronic smoking reveals a suppressed innate immune response and activation of differentiation pathways

Cigarette smoking, a powerful mixture of chemical oxidants, is the strongest environmental risk factor for developing age-related macular degeneration (AMD), the most common cause of blindness among the elderly in western societies. Despite intensive study, the full impact of smoking on the retinal pigment epithelium (RPE), a central cell type involved in AMD pathobiology, remains unknown. The relative contribution of the known dysfunctional pathways to AMD, at what stage they are most pathogenic, or whether other processes are relevant, is poorly understood, and furthermore, whether smoking activates them, is unknown. We performed global RNA-sequencing of the RPE from C57BL/6J mice exposed to chronic cigarette smoke for 6 months to identify potential pathogenic and cytoprotective pathways. The RPE transcriptome induced by chronic cigarette smoking exhibited a mixed response of marked suppression of the innate immune response including type I and II interferons and upregulation of cell differentiation and morphogenic gene clusters, suggesting an attempt by the RPE to maintain its differentiated state despite smoke-induced injury. Given that mice exposed to chronic smoke develop early features of AMD, these novel findings are potentially relevant to the transition from aging to AMD.

Loss of Complement Factor H impairs antioxidant capacity and energy metabolism of human RPE cells

Polymorphisms in the Complement Factor H (CFH) gene, coding for the Factor H protein (FH), can increase the risk for age-related macular degeneration (AMD). AMD-associated CFH risk variants, Y402H in particular, impair FH function leading to complement overactivation. Whether this alone suffices to trigger AMD pathogenesis remains unclear. In AMD, retinal homeostasis is compromised due to the dysfunction of retinal pigment epithelium (RPE) cells. To investigate the impact of endogenous FH loss on RPE cell balance, we silenced CFH in human hTERT-RPE1 cells. FH reduction led to accumulation of C3, at both RNA and protein level and increased RPE vulnerability toward oxidative stress. Mild hydrogen-peroxide exposure in combination with CFH knock-down led to a reduction of glycolysis and mitochondrial respiration, paralleled by an increase in lipid peroxidation, which is a key aspect of AMD pathogenesis. In parallel, cell viability was decreased. The perturbations of energy metabolism were accompanied by transcriptional deregulation of several glucose metabolism genes as well as genes modulating mitochondrial stability. Our data suggest that endogenously produced FH contributes to transcriptional and metabolic homeostasis and protects RPE cells from oxidative stress, highlighting a novel role of FH in AMD pathogenesis.

The association study of lipid metabolism gene polymorphisms with AMD identifies a protective role for APOE-E2 allele in the wet form in a Northern Spanish population

PURPOSE

To elucidate the potential role of eleven single nucleotide polymorphisms (SNPs) in the most relevant lipid metabolism genes in Northern Spanish patients with age-related macular degeneration (AMD).

METHODS

A case-control study of 228 unrelated native Northern Spanish patients diagnosed with AMD (73 dry and 155 wet) and 95 healthy controls was performed. DNA was isolated from peripheral blood and genotyped for the SNPs APOE rs429358 and rs7412; CTEP rs3764261; LIPC rs10468017 and rs493258; LPL rs12678919; ABCA1 rs1883025; ABCA4 rs76157638, rs3112831 and rs1800555; and SCARB1 rs5888, using TaqMan probes. An additional association study of ε2, ε3 and ε4 major isoforms of APOE gene with AMD has been carried out.

RESULTS

The allele and genotype frequencies for each of the eleven sequence variants in the lipid metabolism genes did not show significant differences when comparing AMD cases and controls. Statistical analysis revealed that APOE-ε2 carrier genotypes were less frequently observed in patients with wet AMD compared to controls (5.8% versus 13.7%, respectively: p = 3.28 × 10^-2 ; OR = 0.42, 95% CI: 0.19-0.95). The frequency of the allele T of rs10468017 (LIPC gene) was lower in dry AMD cases compared to controls (15.8 versus 27.9%, respectively: p = 8.4 × 10^-3 OR = 0.57, 95% CI: 0.33-0.98).

CONCLUSIONS

Our results suggest a protective role for APOE-ε2 allele to wet AMD in the Northern Spanish population.

Understanding the complexity of the matrix metalloproteinase system and its relevance to age-related diseases: Age-related macular degeneration and Alzheimer's disease

Extracellular matrices (ECMs) are maintained by tightly coupled processes of continuous synthesis and degradation. The degradative arm is mediated by a family of proteolytic enzymes called the matrix metalloproteinases (MMPs). These enzymes are released as latent proteins (pro-MMPs) and on activation are capable of degrading most components of an ECM. Activity of these enzymes is checked by the presence of tissue inhibitors of MMPs (TIMPs) and current opinion holds that the ratio of TIMPs/MMPs determines the relative rate of degradation. Thus, elevated ratios are thought to compromise degradation leading to the accumulation of abnormal ECM material, whilst diminished ratios are thought to lead to excessive ECM degradation (facilitating angiogenesis and the spread of cancer cells). Our recent work has shown this system to be far more complex. MMP species tend to undergo covalent modification leading to homo- and hetero-dimerization and aggregation resulting in the formation of very large macromolecular weight MMP complexes (LMMCs). In addition, the various MMP species also show a bound-free compartmentalisation. The net result of these changes is to reduce the availability of the latent forms of MMPs for the activation process. An assessment of the degradation potential of the MMP system in any tissue must therefore take into account the degree of sequestration of the latent MMP species, a protocol that has not previously been addressed. Taking into consideration the complexities already described, we will present an analysis of the MMP system in two common neurodegenerative disorders, namely age-related macular degeneration (AMD) and Alzheimer's disease (AD).

Ultrastructural analysis of submacular choriocapillaris and its transport systems in AMD and aged control eyes

The choriocapillaris is the source of nutrients and oxygen for photoreceptors, which consume more oxygen per gram of tissue than any other cell in the body. The purpose of this study was to evaluate and compare the ultrastructure of the choriocapillaris and its transport systems in patients with and without age-related macular degeneration (AMD). Ultrastructural changes were also evaluated in subjects that were homozygous for polymorphisms in high risk CFH alleles (Pure 1) only or homozygous only for high risk ARMS2/HTRA1 (Pure 10) alleles. Tissue samples were obtained from the macular region of forty male (n = 24) and female (n = 16) donor eyes and prepared for ultrastructural studies with transmission electron microscopy (TEM). The average age of the aged donors was 74 ± 7.2 (n = 30) and the young donors 31.7 ± 11.25 (n = 10). There was no significant difference in average ages between the adult groups. TEM images of the capillaries in the choriocapillaris (CC) were taken at 4,000X and 25,000X and used to measure the area of endothelial cell somas, the number of fenestrations, and area of caveolae within the endothelial cells per length of Bruchs membrane (BrMb). The Student t-test and Wilcoxon sum rank test were used to determine significant differences. There was no significant difference between young subjects and aged controls in any of the morphological criteria assessed. There was a significant decrease in the number of fenestrations/mm of BrMb in atrophic areas of GA eyes (p = 0.007) when compared with aged control eyes. A significant increase was found in the caveolae area as a percent of the endothelial cell soma of capillaries from GA subjects as compared with the controls (p = 0.03). Loss of capillary segments in choriocapillaris was also evident, especially in areas of geographic atrophy and CNV. In eyes from patients with sequence variations, the capillary endothelial cells often appeared degenerative and exhibited atypical fenestrations and pericytes covering the blood vessels. Subjects that were homozygous for polymorphisms in high risk CFH alleles only had more fenestrations/mm of BrMb than subjects that were homozygous only for high risk ARMS2/HTRA1 alleles (p = 0.04), while the latter had greater caveolae area/endothelial cell area than the former (p = 0.007). This study demonstrated an attenuation of CC and a significant decline in the two major transport systems in CC endothelial cells in AMD. This may contribute to drusen deposition, nutrient transport, and vision loss in AMD subjects.

Overcoming ocular drug delivery barriers through the use of physical forces

Overcoming the physiological barriers in the eye remains a key obstacle in the field of ocular drug delivery. While ocular barriers naturally have a protective function, they also limit drug entry into the eye. Various pharmaceutical strategies, such as novel formulations and physical force-based techniques, have been investigated to weaken these barriers and transport therapeutic agents effectively to both the anterior and the posterior segments of the eye. This review summarizes and discusses the recent research progress in the field of ocular drug delivery with a focus on the application of physical methods, including electrical fields, sonophoresis, and microneedles, which can enhance penetration efficiency by transiently disrupting the ocular barriers in a minimally or non-invasive manner.

Prognostic implications of imaging in atrophic macular degeneration and its use in clinical practice and clinical trial design

Clinical prognostic markers in atrophic age-related macular degeneration include the extent of existing atrophy, fundus autofluorescence (FAF) patterns and optical coherence tomography changes in the outer retina/retinal pigment epithelium interface. The prognostic implications of these findings may be used to determine not just the rate of disease progression but also influence the likelihood, magnitude and clinical relevance of therapy responses. FAF phenotypes have been extensively investigated; however, the pathophysiological mechanisms behind their appearance have not been fully elucidated. Optical coherence tomography imaging is additive to FAF imaging in atrophic age-related macular degeneration, allowing the visualization of detail not available through FAF imaging whilst also displaying subtle changes correlating with the FAF phenotypes themselves, thereby giving clues to their histological determinates. The developing understanding of these imaging modalities and consequent development of prognostically useful classification systems have widespread implication in clinical care and clinical trial design.

The 2014 Bowman Lecture-Bowman's and Bruch's: a tale of two membranes during the laser revolution

To describe the historical evolution of the role of lasers in effecting therapeutic changes in the four acellular membranes of the eye. Over the past 50 years, iterative developments have been instituted in lasers used for various forms of eye surgery predominately on the basis of data generated in early experiments in the 1960s to determine thresholds for damage and their incorporation in codes of practice for laser safety. The evolutionary steps are described. Excimer laser technology resulted in the generation of the new field of laser refractive surgery with over 40 million individuals now having undergone procedures such as photorefractive keratectomy and LASIK. Developments in lasers used for various forms of retinal surgery have undergone changes involving shorter and shorter pulse durations together with changes in beam energy distribution with implications for potential intervention in AMD prophylactically. Lasers have made a major impact on surgical treatment on all four acellular membranes of the eye but particularly Bowman's membrane in refractive surgery, where it has been demonstrated that it can be removed without significant consequences for eye health or vision.

Subcellular distribution and activity of mechanistic target of rapamycin in aged retinal pigment epithelium

PURPOSE

Inhibiting mechanistic target of rapamycin (mTOR) by pharmacological or genetic approaches can extend lifespan in mammals. The kinase activity of mTOR is controlled by upstream regulatory proteins and its subcellular localization. The purpose of this study was to characterize age-related alterations and functional consequences of mTOR signaling in the postmitotic RPE cells.

METHODS

Activity of mTOR complex 1 (mTORC1) was monitored by measuring phosphorylation status of its downstream effector protein S6, in either cultured human RPE cells or RPE explants prepared from mice at different ages. Subcellular distribution of mTOR was investigated by immunofluorescent staining of RPE culture or flatmount. The signaling of mTORC1 was modulated by either overexpression of a small guanosine triphosphatase, Ras homolog enriched in brain (Rheb), or disruption of the Ragulator complex with small interference RNA targeting p18. The effects of mTOR pathway on degradation of phagocytosed photoreceptor outer segments (POS) were determined by measuring the turnover rate of rhodopsin.

RESULTS

Aged RPE cells had more lysosome-associated mTOR and had increased response to amino acid stimulation. The lysosome distribution was essential for mTORC1 function, as disruption of the Ragulator complex abolished mTORC1 activation by amino acids. Increased mTORC1 activity caused decreased rate of degradation of internalized POS in the RPE.

CONCLUSIONS

Aging changes the subcellular localization and function of mTOR in the RPE. Increased mTORC1 inhibits POS degradation and may further exacerbate lysosome dysfunction of aged RPE.

Age-related macular degeneration and changes in the extracellular matrix

Age-related macular degeneration (AMD) is the leading cause of permanent, irreversible, central blindness (scotoma in the central visual field that makes reading and writing impossible, stereoscopic vision, recognition of colors and details) in patients over the age of 50 years in European and North America countries, and an important role is attributed to disorders in the regulation of the extracellular matrix (ECM). The main aim of this article is to present the crucial processes that occur on the level of Bruch’s membrane, with special consideration of the metalloproteinase substrates, metalloproteinase, and tissue inhibitor of metalloproteinase (TIMP).

A comprehensive review of the literature was performed through MEDLINE and PubMed searches, covering the years 2005–2012, using the following keywords: AMD, extracellular matrix, metalloproteinases, tissue inhibitors of metalloproteinases, Bruch’s membrane, collagen, elastin.

In the pathogenesis of AMD, a significant role is played by collagen type I and type IV; elastin; fibulin-3, -5, and -6; matrix metalloproteinase (MMP)-2, MMP-9, MMP-14, and MMP-1; and TIMP-3. Other important mechanisms include: ARMS2 and HTR1 proteins, the complement system, the urokinase plasminogen activator system, and pro-renin receptor activation.

Continuous rebuilding of the extracellular matrix occurs in both early and advanced AMD, simultaneously with the dysfunction of retinal pigment epithelium (RPE) cells and endothelial cells. The pathological degradation or accumulation of ECM structural components are caused by impairment or hyperactivity of specific MMPs/TIMPs complexes, and is also endangered by the influence of other mechanisms connected with both genetic and environmental factors.

Prediction of passive drug permeability across the blood-retinal barrier

PURPOSE

The purpose of this study is to develop a computational model of the physical barrier function of the outer blood-retinal barrier (BRB), which is vital for normal retinal function. To our best knowledge no comprehensive models of BRB has been reported.

METHODS

The model construction is based on the three-layered structure of the BRB: retinal pigment epithelium (RPE), Bruch's membrane and choriocapillaris endothelium. Their permeabilities were calculated based on the physical theories and experimental material and permeability studies in the literature, which were used to describe diffusional hindrance in specific environments.

RESULTS

Our compartmental BRB model predicts permeabilities with magnitudes similar to the experimental values in the literature. However, due to the small number and varying experimental conditions there is a large variability in the available experimental data, rendering validation of the model difficult. The model suggests that the paracellular pathway of the RPE largely defines the total BRB permeability.

CONCLUSIONS

Our model is the first BRB model of its level and combines the present knowledge of the BRB barrier function. Furthermore, the model forms a platform for the future model development to be used for the design of new drugs and drug administration systems.

Spectral domain optical coherence tomography-determined morphologic predictors of age-related macular degeneration-associated geographic atrophy progression

PURPOSE

To correlate spectral domain optical coherence tomography (SD OCT)-determined morphologic alterations in eyes with geographic atrophy because of age-related macular degeneration with lesion size, enlargement rate, and the presence of multifocal patches of atrophy.

METHODS

Forty-three eyes of 43 patients with age-related macular degeneration-associated geographic atrophy were visualized by SD OCT and fundus autofluorescence imaging. The baseline area of geographic atrophy and enlargement rates over at least 24 weeks were calculated from the fundus autofluorescence images. The mean and median follow-up times were 47.4 and 48 weeks, respectively. Morphologic alterations were evaluated in the baseline SD OCT images. Ninety-seven SD OCT scans per eye were graded and included in the analysis. Correlations between morphologic alterations and the rate of lesion enlargement, size, and focality, and the diffuse trickling fundus autofluorescence pattern were determined.

RESULTS

The mean and median enlargement rates were 2.07 mm(2)/year (n = 43; SD, 1.30) and 2.02 mm(2)/year, respectively. Outer retinal tubulations (P = 0.003) and irregular elevations of the retinal pigment epithelium/Bruch membrane complex (P < 0.001) in the atrophic region, and splitting of the retinal pigment epithelium/Bruch membrane complex at 2 junctional zone borders (P = 0.02) correlated with faster enlargement. Outer retinal tubulations (P = 0.096), irregular elevations of the retinal pigment epithelium/Bruch membrane complex (P = 0.010), and crown-like elevations with debris beneath in the atrophic region (P = 0.063) correlated with larger lesion size. Hyperreflective plaques in the outer retina appeared more frequently in eyes with multifocal patches of atrophy (P = 0.005).

CONCLUSION

Distinct morphologic alterations visible on SD OCT imaging in eyes with geographic atrophy because of age-related macular degeneration are associated with faster enlargement rates, larger lesion size, and multifocal patches of atrophy.

Chronologic versus biologic aging of the human choroid

Several aspects of chronologic and biologic aging in the human choroid are reviewed from the literature. They often reveal methodological problems for age-dependent changes of the following parameters: choroidal thickness, choroidal pigmentation, choroidal vasculature and blood flow, and choroidal innervation. On reinterpreting some data of studies concerning Bruch's membrane, changes observed at different age points seem more likely to be nonlinear. Concluding from the data presented so far, chronologic aging should not be used as a factor for physiological changes in the human choroid. Longitudinal study designs are necessary to further establish the impact of age. Meanwhile, a more biologic oriented model of aging processes in the choroid should be established, including specified conditions (e.g., light exposure and refractory state). This would help to define more individual strategies for prevention and early stages of a certain defined disease.

Aging is not a disease: distinguishing age-related macular degeneration from aging

Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.

Delivery of intraocular triamcinolone acetonide in the treatment of macular edema

Macular edema (ME) is one of the eventual outcomes of various intraocular and systemic pathologies. The pathogenesis for ME is not yet entirely understood; however, some of the common risk factors for its development have been identified. While this investigation will not discuss the numerous etiologies of ME in detail, it appraises the two most widely studied delivery modalities of intraocular corticosteroids in the treatment of ME—intravitreal injection (IVI) and sub-Tenon’s infusion (STI). A thorough review of the medical literature was conducted to identify the efficacy and safety of IVI and STI, specifically for the administration of triamcinolone acetonide (TA), in the setting of ME in an attempt to elucidate a preferred steroid delivery modality for treatment of ME.

Passage of low-density lipoproteins through Bruch's membrane and choroid

Plasma lipoproteins are thought to transport cholesterol, vitamins and carotenoids to the retinal pigment epithelium (RPE) for ultimate use by the photoreceptors. However, to reach the RPE, these lipoprotein particles must cross Bruch's membrane. We examined the reflection coefficient of Bruch's membrane (BrM) to low-density lipoprotein (LDL). Bruch's membrane and choroid were removed from 47 bovine eyes. Specimens were placed in a Ussing chamber and perfused with phosphate-buffered saline (PBS) with (31 specimens) or without (16 specimens) fluorescent low-density lipoproteins (DiI-LDL). The hydraulic conductivity of the tissue was determined for both calf and cow eyes. In the perfusions with DiI-LDL, the fluorescence intensity emitted by DiI-LDL in the efflux was measured and the reflection coefficient of BrM/choroid preparations to DiI-LDL determined. Leakage tests were done to confirm tissue integrity. Several specimens were examined using scanning electron microscopy (SEM) to examine tissue integrity before and after perfusion. Leak testing confirmed that BrM was intact both before and after perfusion. The average hydraulic conductivity of BrM/choroid perfusion of calf eyes with PBS alone was 1.42 ± 0.55 × 10(-9) m/s/Pa (mean ± SD, n = 11). The average hydraulic conductivity of the cow eyes was 4.94 ± 1.48 × 10(-10) m/s/Pa (n = 5), nearly a 3-fold decrease with age. While the flow rate remained constant during the PBS perfusions, it decreased as a function of time during perfusion with DiI-LDLs. Our major finding was of fluorescence in the effluent collected in all perfusions with DiI-LDLs, demonstrating passage of LDL through the tissue. The average reflection coefficient of calf BrM/choroid preparations to DiI-LDL was 0.58 ± 0.25 (n = 23); a similar distribution of reflection coefficients was seen in tissue from cow eyes (0.51 ± 0.33, n = 8). Our data suggested that the DiI-LDL was modestly hindered and/or captured by the tissue. This might explain the progressive decrease of hydraulic conductivity with continued perfusion of DiI-LDL.

Relationship of stokes radius to the rate of diffusion across Bruch's membrane

PURPOSE

To determine the effect of Stokes radius (R(S)) on the diffusion of molecules through Bruch's membrane (BM), and to establish a system suitable for the analysis of diffusion through small (<2 mm(2)) samples of BM.

METHODS

Porcine BM/choroid (BM/Ch) was mounted in a modified Ussing chamber. A concentration gradient was simultaneously established for four tracers with R(S) values ranging from <1.0 to 6.15 nm. Samples were collected from both chambers at various time points up to 36 hours and the amount of each tracer was determined using quantitative gel exclusion chromatography. The integrity of samples was determined using scanning electron microscopy.

RESULTS

BM/Ch mounted in the chamber exhibited no obvious damage even after 36 hours in the chamber. Flux was significantly (P < 0.05) greater in the BM to Ch direction than that in the Ch to BM direction for only two of the tracers: cytosine and RNase A. Flux also was dependent on R(S); cytosine, the smallest tracer (R(S) < 1 nm), exhibited the greatest flux and ferritin (R(S) = 6.15 nm) the least. Permeability coefficients for each tracer were determined and exhibited a power relationship with R(S).

CONCLUSIONS

Flux was dependent on the direction of the concentration gradient and the R(S) of the individual tracers. We have successfully demonstrated that quantitative gel exclusion chromatography can be used to follow diffusion of a mixture of tracers across BM/Ch, and that we can measure flux across BM/Ch preparations with an exposed surface area as small as 1.8 mm(2).

Fundus autofluorescence and spectral-domain optical coherence tomography characteristics in a rapidly progressing form of geographic atrophy

PURPOSE

To further characterize a previously described phenotypic variant of geographic atrophy (GA) associated with rapid progression and a diffuse-trickling appearance on fundus autofluorescence (FAF).

METHODS

Thirty-six patients (60 eyes; 72.2% women; mean age, 69.4 ± 10.7 years) with this distinct phenotype were examined by simultaneous confocal scanning laser ophthalmoscopy (cSLO) and spectral-domain optical coherence tomography (SD-OCT) imaging. Images were qualitatively and quantitatively analyzed and compared with 60 eyes (38 patients) with non diffuse-trickling GA.

RESULTS

The atrophic area in the diffuse-trickling phenotype showed a grayish FAF signal and characteristic coalescent lobular configuration at the lesion boundaries. SD-OCT revealed a marked splitting of band 4 (the presumptive retinal pigment epithelium (RPE)/Bruch's membrane (BM) complex) in all 240 analyzed border sections of diffuse-trickling GA eyes (four borders/eye) with a mean distance between the inner and outer parts of band 4 of 23.2 ± 7.5 μm. This finding was present in only 13.8% (33/240) of analyzed border sections in non diffuse-trickling GA.

CONCLUSIONS

Patients with the rapidly progressing diffuse-trickling GA phenotype exhibited a characteristic marked separation within the RPE/BM complex on SD-OCT-imaging. The presumed histopathologic correlates are basal laminar deposits. Such deposits may promote RPE cell death and, thus, contribute to rapid GA progression. The persistence of these deposits within the atrophic lesion may account for the distinct grayish FAF appearance, which differs from the markedly reduced signal in other forms of GA. Identification of such alterations based on FAF and SD-OCT imaging may be helpful in future interventional trials directed toward slowing GA progression. (ClinicalTrials.gov number, NCT00393692.).

A hapten generated from an oxidation fragment of docosahexaenoic acid is sufficient to initiate age-related macular degeneration

The protein adduct carboxyethylpyrrole (CEP) is present in age-related macular degeneration (AMD) eye tissue and in the blood of AMD patients at higher levels than found in age-matched non-AMD tissues. Autoantibodies to CEP are also higher in AMD blood samples than in controls. To test the hypothesis that this hapten is causally involved in initiating an inflammatory response in AMD, we immunized C57BL/6J mice with mouse serum albumin (MSA) adducted with CEP. Immunized mice develop antibodies to CEP, fix complement component-3 in Bruch's membrane, accumulate drusen below the retinal pigment epithelium during aging, show decreased a- and b-wave amplitudes in response to light, and develop lesions in the retinal pigment epithelium mimicking geographic atrophy, the blinding end-stage condition characteristic of the dry form of AMD. Inflammatory cells are present in the region of lesions and may be actively involved in the pathology observed. We conclude that early immunization of mice with CEP-adducted MSA sensitizes these animals to the ongoing production of CEP adducts in the outer retina where DHA is abundant and the conditions for oxidative damage are permissive. In response to this early sensitization, the immune system mounts a complement-mediated attack on the cells of the outer retina where CEP adducts are formed. This animal model for AMD is the first that was developed from an inflammatory signal discovered in eye tissue and blood from AMD patients. It provides a novel opportunity for dissecting the early pathology of AMD and the immune response contributing to this disorder. The availability of a mouse with a mechanistically based AMD-like disease that progresses rapidly is highly desirable. Such a model will allow for the efficient preclinical testing of the much-needed therapeutics quickly and inexpensively.

Aging, age-related macular degeneration, and the response-to-retention of apolipoprotein B-containing lipoproteins

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. A prominent age-related change in the human retina is the accumulation of histochemically detectable neutral lipid in normal Bruch's membrane (BrM) throughout adulthood. This change has the potential to have a major impact on physiology of the retinal pigment epithelium (RPE). It occurs in the same compartment as drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD. Here we present evidence from light microscopic histochemistry, ultrastructure, lipid profiling of tissues and isolated lipoproteins, and gene expression analysis that this deposition can be accounted for by esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles constitutively produced by the RPE. This work collectively allows ARMD lesion formation and its aftermath to be conceptualized as a response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (CAD) (Tabas et al., 2007). This approach provides a wide knowledge base and sophisticated clinical armamentarium that can be readily exploited for the development of new model systems and the future benefit of ARMD patients.

Apolipoprotein B-containing lipoproteins in retinal aging and age-related macular degeneration

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. With aging, there is a striking accumulation of neutral lipids in Bruch's membrane (BrM) of normal eye that continues through adulthood. This accumulation has the potential to significantly impact the physiology of the retinal pigment epithelium (RPE). It also ultimately leads to the creation of a lipid wall at the same locations where drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD, subsequently form. Here, we summarize evidence obtained from light microscopy, ultrastructural studies, lipid histochemistry, assay of isolated lipoproteins, and gene expression analysis. These studies suggest that lipid deposition in BrM is at least partially due to accumulation of esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles produced by the RPE. Furthermore, we suggest that the formation of ARMD lesions and their aftermath may be a pathological response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (Tabas, I., K. J. Williams, and J. Borén. 2007. Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications. Circulation. 116:1832-1844). This view provides a conceptual basis for the development of novel treatments that may benefit ARMD patients in the future.

Preservation of retinoid influx into eye tissues of ABCR-deficient mice

Using an in vivo radiolabeling technique, we investigated the movement of retinoid into the retinal pigment epithelium (RPE) of the abcr-/- mouse, which lacks the photoreceptor ABCR protein and is a model for Stargardt disease. Eye tissues and serum obtained from dark-adapted, 5- to 8-month-old abcr-/- and control mice following the intraperitoneal injection of all-trans ((3)H)retinol were analyzed to determine the inferred influx of retinoid from the serum into the RPE. At 4.5 hr post-injection, the inferred all-trans retinol influx in abcr-/- mice, which possess the leucine 450 variant of RPE65 protein, was 0.011 +/- 0.004 nmol (n = 3). This value did not differ significantly from that determined in age-matched controls possessing the methionine 450 variant of RPE65 (0.015 +/- 0.003 nmol; n = 3) or from 3-month-old wildtype mice that possess the leucine 450 RPE65 variant (0.020 +/- 0.007; n = 4). Thus, the absence of ABCR does not significantly compromise the passage of retinoid from the serum into the RPE under dark-adapted conditions.

Transport barriers in transscleral drug delivery for retinal diseases

Transscleral delivery has emerged as an attractive method for treating retinal disorders because it offers localized delivery of drugs as a less invasive method compared to intravitreal administration. Numerous novel transscleral drug delivery systems ranging from microparticles to implants have been reported. However, transscleral delivery is currently not as clinically effective as intravitreal delivery in the treatment of retinal diseases. Transscleral drug delivery systems require drugs to permeate through several layers of ocular tissue (sclera, Bruch's membrane-choroid, retinal pigment epithelium) to reach the neuroretina. As a result, a steep drug concentration gradient from the sclera to the retina is established, and very low concentrations of drug are detected in the retina. This steep gradient is created by the barriers to transport that hinder drug molecules from successfully reaching the retina. A review of the literature reveals 3 types of barriers hindering transscleral drug delivery: static, dynamic and metabolic. While static barriers have been examined in detail, the literature on dynamic and metabolic barriers is lacking. These barriers must be investigated further to gain a more complete understanding of the transport barriers involved in transscleral drug delivery.

Age-related changes in human macular Bruch's membrane as seen by quick-freeze/deep-etch

Lipid-containing inclusions have been observed in human Bruch's membrane (BrM) and are postulated to be associated with age-related maculopathy (ARM), a major cause of legal blindness in developed countries. The dehydration associated with specimen preparation for thin-section transmission electron microscopy causes loss of these inclusions. Better preservation of the ultrastructure of the inclusions and tissue is achieved by using a quick-freeze/deep-etch preparation. We use this technique to examine normal human macular BrM in order to characterize the deposition of the lipid-rich inclusions and their age-related accumulation within different layers of the tissue. We find that various inclusions mentioned in other studies can be formed by combinations of three basic structures: lipoprotein-like particles (LLPs), small granules (SGs) and membrane-like structures. These inclusions are associated with collagen and elastic fibrils by fine filaments. In younger eyes, these inclusions are found mostly in the elastic (EL) and outer collageneous layer (OCL) and occupy a small fraction of the interfibrillar spacing. As age increases, LLPs and SGs gradually fill the interfibrillar spacing of the EL and inner collageneous layer (ICL) of the tissue, and later form a new sublayer, the lipid wall, within the boundary region between the basal lamina of retinal pigment epithelium (RPE) and ICL. Because the formation of the lipid wall only occurs after these inclusions fill the ICL, and it seems unlikely that the LLPs can pass through the packed layer, this result suggests a possible RPE origin of the LLPs that make up the lipid wall.

Transscleral drug delivery to the posterior eye: prospects of pharmacokinetic modeling

Basic biological research has provided new approaches to treat severe diseases of the retina and choroid, such as age related macular degeneration. Although it is possible to deliver drugs from a subconjunctival drug depot to the retina and choroid, the barriers and kinetics of this route of drug administration are not well known. In this review we investigate the pharmacokinetic aspects of transscleral drug delivery into the posterior eye with emphasis on pharmacokinetic modeling. The existing simulation models related to the transscleral drug delivery are reviewed and future directions for the model development are discussed. In addition, a new simulation model for the transscleral drug delivery based on permeability data is introduced. This compartmental model contains several ocular tissues (sclera, choroid, retinal pigment epithelium and vitreous) and it takes into account the clearance of the drug via choroidal circulation. The model is used to simulate the vitreous delivery of macromolecules based on the available data on FITC-dextran 70 kDa.

Bovine and porcine transscleral solute transport: influence of lipophilicity and the Choroid-Bruch's layer

PURPOSE

To determine the influence of the choroid-Bruch's layer and solute lipophilicity on in vitro transscleral drug permeability in bovine and porcine eyes.

METHODS

The in vitro permeability of two VEGF inhibitory drugs, budesonide and celecoxib, which are lipophilic and neutral at physiologic pH, and of three marker solutes, 3H-mannitol (hydrophilic, neutral), sodium fluorescein (hydrophilic, anionic), and rhodamine 6G (lipophilic, cationic), were determined across freshly excised scleras, with or without the underlying choroid-Bruch's layer. Select studies were performed using porcine sclera with and without choroid-Bruch's layer. Neural retina was removed by exposure of the eyecup to isotonic buffer and wherever required, the retinal pigment epithelial (RPE) layer of the preparation was disrupted and removed by exposure to hypertonic buffer. Because of the poor solubility of celecoxib and budesonide, permeability studies were conducted with 5% wt/vol of hydroxypropyl-beta-cyclodextrin (HPbetaCD). For other solutes, permeability studies were conducted, with and without HPbetaCD. Partitioning of the solutes into bovine sclera and choroid-Bruch's layer was also determined.

RESULTS

The calculated log (distribution coefficient) values were -2.89, -0.68, 2.18, 3.12, and 4.02 for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G, respectively. Removal of RPE was confirmed by transmission electron microscopy and differences in the transport of mannitol. The order of the permeability coefficients (Papp) across sclera and sclera-choroid-Bruch's layers in bovine and porcine models was 3H-mannitol > fluorescein > budesonide > celecoxib > rhodamine 6G, with HPbetaCD, and 3H-mannitol > fluorescein > rhodamine 6G, without HPbetaCD. The presence of choroid-Bruch's layer reduced the bovine scleral permeability by 2-, 8-, 16-, 36-, and 50-fold and porcine tissue permeability by 2-, 7-, 15-, 33-, and 40-fold, respectively, for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G. The partition coefficients measured in bovine tissues correlated positively with the log (distribution coefficient) and exhibited a trend opposite that of transport. The partition coefficient ratio of bovine choroid-Bruch's layer to sclera was approximately 1, 1.5, 1.7, 2, and 3.5, respectively, for the solutes, as listed earlier.

CONCLUSIONS

The choroid-Bruch's layer is a more significant barrier to drug transport than is sclera. It hinders the transport of lipophilic solutes, especially a cationic solute, more than hydrophilic solutes and in a more dramatic way than does sclera. The reduction in transport across this layer directly correlates with solute binding to the tissue. Understanding the permeability properties of sclera and underlying layers would be beneficial in designing better drugs for transscleral delivery.

An experimental study of the elastic properties of the human Bruch's membrane-choroid complex: relevance to ageing

AIM

To investigate the mechanical properties (stress-strain relation, elasticity, hysteresis, response to stress spikes and drops) of isolated human Bruch's membrane-choroid, as well as the effect of ageing and aged related macular degeneration (AMD).

METHODS

13 Bruch's membrane-choroid complexes were obtained from human donors (21-97 years). Two samples (aged 85 and 95) showed signs of AMD including large, soft drusen, choroidal neovascularisation, and/or disciform scars. Various hydrostatic pressures (stress) were applied to the choroidal surface of mid-peripheral samples mounted in a modified open Ussing chamber. Linear scans of the tissue were recorded by optical coherence tomography (OCT) and the pressure induced deformation (strain), elasticity, hysteresis, and response to pressure spikes and drops measured.

RESULTS

The elasticity of human Bruch's membrane-choroid complex decreased linearly with ageing (p<0.001) after the age of 21 with an approximate reduction of 1% per year. The decrease was not exaggerated in AMD. The recoil capacity of Bruch's membrane-choroid was not affected by ageing. The response to pressure spikes/drops was similar in age matched normal and AMD eyes. The results suggest that although the aged induced decrease in Bruch's membrane elasticity may contribute to breaks in this membrane in AMD leading to neovascularisation this is not sufficient. The presence of other factors is required for its development.

CONCLUSION

The elasticity of Bruch's membrane-choroid complex decreases with age while recoil capacity does not. The decrease was not exaggerated in AMD.

Age-related macular degeneration--emerging pathogenetic and therapeutic concepts

Today, the average life expectancy in developed nations is over 80 years and climbing. And yet, the quality of life during those additional years is often significantly diminished by the effects of age-related, degenerative diseases, including age-related macular degeneration (AMD), the leading cause of blindness in the elderly worldwide. AMD is characterized by a progressive loss of central vision attributable to degenerative and neovascular changes in the macula, a highly specialized region of the ocular retina responsible for fine visual acuity. Estimates gathered from the most recent World Health Organization (WHO) global eye disease survey conservatively indicate that 14 million persons are blind or severely visually impaired because of AMD. The disease has a tremendous impact on the physical and mental health of the geriatric population and their families and is becoming a major public health burden. Currently, there is neither a cure nor a means to prevent AMD. Palliative treatment options for the less prevalent, late-stage 'wet' form of the disease include anti-neovascular agents, photodynamic therapy and thermal laser. There are no current therapies for the more common 'dry' AMD, except for the use of antioxidants that delay progression in 20%-25% of eyes. New discoveries, however, are beginning to provide a much clearer picture of the relevant cellular events, genetic factors, and biochemical processes associated with early AMD. Recently, compelling evidence has emerged that the innate immune system and, more specifically, uncontrolled regulation of the complement alternative pathway plays a central role in the pathobiology of AMD. The complement Factor H gene--which encodes the major inhibitor of the complement alternative pathway--is the first gene identified in multiple independent studies that confers a significant genetic risk for the development of AMD. The emergence of this new paradigm of AMD pathogenesis should hasten the development of novel diagnostic and therapeutic approaches for this disease that will dramatically improve the quality of our prolonged lifespan.

Inhibition of lysosomal degradation in retinal pigment epithelium cells induces exocytosis of phagocytic residual material at the basolateral plasma membrane

PURPOSE

To analyze chloroquine-induced morphological changes in the retinal pigment epithelium (RPE) and Bruch's membrane (BM).

METHODS

Retina-choroid complexes of chloroquine-treated Long-Evans rats were analyzed by electron microscopy.

RESULTS

Intercellular spaces between the RPE cells and BM were enlarged. Residual material from phagosomes was released into these enlarged spaces. Debris accumulated within BM and encircled choriocapillaris endothelial cells.

CONCLUSION

There is a release of undegraded phagocytic material (rod outer segments) into the extracellular space between BM and RPE cells, following inhibition of lysosomal degradation. Electron-dense deposits in BM and choriocapillaris may lead to reduced oxygen and nutrition flow.

Rheopheresis for age-related macular degeneration: clinical results and putative mechanism of action

BACKGROUND

Rheopheresis is being evaluated in a clinical trial. The rationale and available results are presented.

METHODS

We reviewed the literature about the pathophysiology of age-related macular degeneration (AMD) that might support the use of rheopheresis. In addition, we reviewed the previously published results of the use of rheopheresis for AMD.

RESULTS

There appears to be a diffusion barrier caused by accumulation of cross-linked proteins known as advanced macular oxidation products (AMOPS) in AMD. Rheopheresis allows removal of uncross-linked proteins and facilitates antioxidant entry into Bruch's membrane, preventing further accumulation of AMOPS. The Multicenter Investigation of Rheopheresis for AMD (MIRA-1), an ongoing double-masked randomized trial, should determine the efficacy of rheopheresis in preventing the progression of AMD. The interim results, from an analysis of visual acuity data for 43 patients, are encouraging, confirming the potential of rheopheresis as a therapeutic option for dry AMD. The benefit was evident immediately after treatment and remained essentially stable throughout the 12-month period of evaluation. Eyes with late-stage, high-risk, dry AMD appeared to be at significant risk for substantial vision loss over the 12 months if not treated. Subgroup analysis demonstrated that the timing of rheopheresis in the course of a patient's disease may have a pronounced effect on outcome.

INTERPRETATION

There appears to be a rationale for the use of rheopheresis in AMD. Further results of the clinical trial are awaited.

Decreased thickness and integrity of the macular elastic layer of Bruch's membrane correspond to the distribution of lesions associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in the elderly. In its severest form, choroidal neovessels breach the macular Bruch's membrane, an extracellular matrix compartment comprised of elastin and collagen laminae, and grow into the retina. We sought to determine whether structural properties of the elastic lamina (EL) correspond to the region of the macula that is predilected toward degeneration in AMD. Morphometric assessment of the macular and extramacular regions of 121 human donor eyes, with and without AMD, revealed a statistically significant difference in both the integrity (P < 0.0001) and thickness (P < 0.0001) of the EL between the macular and extramacular regions in donors of all ages. The EL was three to six times thinner and two to five times less abundant in the macula than in the periphery. The integrity of the macular EL was significantly lower in donors with early-stage AMD (P = 0.028), active choroidal neovascularization (P = 0.020), and disciform scars (P = 0.003), as compared to unaffected, age-matched controls. EL thickness was significantly lower only in individuals with disciform scars (P = 0.008). The largest gaps in macular EL integrity were significantly larger in all categories of AMD (each P < 0.0001), as compared to controls. EL integrity, thickness, and gap length in donors with geographic atrophy did not differ from those of controls. These structural properties of the macular EL correspond spatially to the distribution of macular lesions associated with AMD and may help to explain why the macula is more susceptible to degenerative events that occur in this disease.

Clinical outcomes and mechanism of action for rheopheresis treatment of age-related macular degeneration (AMD)

The primary goals are to provide a comprehensive explanation of the potential role of therapeutic apheresis in the treatment of Age-Related Macular Degeneration (AMD). Initial clinical results with this technique and a summary of current literature that addresses the mechanism of action for the Rheopheresis approach are presented. Rheopheresis has been found to be a safe and effective application of double filtration plasmapheresis (DFPP) for extracorporeal hemorheotherapy. In this report, it is proposed that Rheopheresis results in an immediate decrease in the proportion of high molecular weight proteins that could combine with the TIMP-3 fibulin complex allowing for the barely functioning retinal pigment epithelial (RPE) cells to function better and diminish the release of vascular endothelial growth factor (VEGF). Interim results from the randomized, double-masked MIRA-1 clinical trial include (1) improved vision restoration; 28.0% of Treated Primary Eyes increased by > or = 2 lines of best corrected visual acuity (BCVA) compared to 18.2% of Placebo Eyes; (2) a decline in progressive vision loss; 0.0% of treated eyes progressing to worse than 20/200 vision over the 12-month study compared to 18.2% of Placebo Eyes; (3) 57.9% of Treatment Eyes obtained improvement in their BCVA to 20/40 or better (driver's license qualification), compared to only 14.3% of Placebo Eyes 12-month post-treatment. Rheopheresis treatment shows strong promise as a viable clinical option for patients suffering from the dry form of AMD in terms of minimizing vision loss, vision restoration, and overall quality of life factors. Expanded clinical outcomes from the ongoing MIRA-1 clinical study will be valuable in the assessment of this new clinical tool for ophthalmic applications.

Retinectomy for treatment of intractable glaucoma: long term results

AIM

To report long term efficacy and complications of retinectomy as an intraocular pressure lowering procedure for intractable glaucoma.

METHODS

This was a consecutive interventional case series. In 44 consecutive eyes (39 patients, 22 men and 17 women) retinectomy was performed to lower the intraocular pressure (IOP) in patients with uncontrolled IOP (>35 mm Hg for more than 4 months) despite conventional filtering surgery and drug treatment. Pars plana vitrectomy was performed and the peripheral retina was surgically excised to various degrees. The procedure was concluded by an intraocular gas tamponade of 20% C(3)F(8). Included were patients with neovascular glaucoma (12 eyes), infantile and juvenile glaucoma (three eyes), secondary glaucoma due to aphakia (13 eyes), severe ocular trauma (seven eyes), uveitis (seven eyes), and glaucoma in Ehlers-Danlos syndrome (two).

RESULTS

All patients underwent successful surgical retinectomy. All patients were followed for 5 years. Mean postoperative IOP after 4 years was 15.7 (SD 9.4) mm Hg, representing a decrease of IOP by 61% compared to the preoperative level (41.2 (9.4) mm Hg). In 52.3% of eyes long term regulation of IOP could be achieved without complications. Retinectomy was least effective in neovascular glaucoma because of central retinal vein occlusion (CRVO). Eyes with glaucoma secondary to uveitis showed a tendency towards low IOP levels with subsequent phthisis bulbi. The initial visual acuity of all patients was lower than 20/50 (mean 1.8 (0.8) logMAR) in the treated eye. Final visual acuity was 2.3 (0.6) logMAR. 21 out of 44 cases developed retinal complications (retinal detachment or proliferative vitreoretinopathy (PVR)) after surgery, requiring silicone tamponade in 11 eyes (52%) either for persistent low IOP or for PVR. Nine eyes developed phthisis, seven of which were enucleated during the follow up.

CONCLUSIONS

Long term results after retinectomy demonstrate its efficacy in otherwise intractable glaucoma. Efficacy and safety of retinectomy are dependent on the underlying disease.

Clinical studies to implement Rheopheresis for age-related macular degeneration guided by evidence-based-medicine

In the majority of age-related macular degeneration (AMD) patients the therapeutic situation is very unsatisfactory, especially for patients with dry AMD. Rheopheresis is a safe and effective modality of therapeutic apheresis to treat microcirculatory disorders, and represents a novel therapeutic approach for patients with dry AMD and soft drusen. Elimination of a defined spectrum of high molecular weight proteins from human plasma including pathophysiologically relevant risk factors for AMD such as fibrinogen, LDL-cholesterol, alpha 2-macroglobulin, fibronectin, and von-Willebrand factor results in the reduction of blood and plasma viscosity as well as erythrocyte and thrombocyte aggregation. Pulses of lowering blood and plasma viscosity performed as series of Rheopheresis treatments lead to rapid changes of blood flow, subsequently inducing sustained improvement of microcirculation, and recovery of retinal function. Two controlled randomized clinical trials demonstrated safety and efficacy of Rheopheresis for the treatment of AMD patients, especially with the dry form. Recently the interim-analysis of the sham-controlled, double blinded, randomized multicenter MIRA-I trial confirmed these results. The RheoNet-registry and the development and continuous update of therapy guidelines provide an appropriate framework for the quality management of the interdisciplinary cooperation between ophthalmologists with apheresis specialists. A hypothesis based upon current knowledge of pathogenic mechanisms of the development and progression of AMD can be conclusively linked with the putative mechanism of action of Rheopheresis for AMD. A recommendation for high-risk AMD-patients was defined. Based on the positive results of the MIRA-1 interim analysis eight Rheopheresis treatments are currently recommended as the initial treatment series.

Photoreceptor degeneration and dysfunction in aging and age-related maculopathy

The relative rate of rod and cone degeneration is a fundamental characteristic of any disorder affecting photoreceptors, including aging and age-related maculopathy (ARM). The human macula consists of a small cone-dominated fovea surrounded by a rod-dominated parafovea. In aging and early ARM, rods degenerate before cones, a decline in scotopic (rod-mediated) sensitivity is more prominent than a decline in photopic (cone-mediated) sensitivity, and the time course of dark adaptation of rods slows dramatically. The topography of rod dysfunction and loss in early ARM matches the location of pathology in the retinal pigment epithelium (RPE)/Bruch's membrane complex visible in the ocular fundus. Rod dysfunction and loss in aging and ARM may be due to retinoid deficiency at the level of the photoreceptors cause by impaired retinoid translocation across the RPE/Bruch's membrane complex, a hypothesis deserving of further investigation.