Maculoplasty for age-related macular degeneration: reengineering Bruch's membrane and the human macula

Age-related macular degeneration (AMD) is the leading cause of blindness in the western world. Over the last decade, there have been significant advances in the management of exudative AMD with the introduction of anti-VEGF drugs; however, many patients with exudative AMD continue to lose vision and there are no effective treatments for advanced exudative AMD or geographic atrophy. Initial attempts at macular reconstruction using cellular transplantation have not been effective in reversing vision loss. Herein we discuss the current status of surgical attempts to reconstruct damaged subretinal anatomy in advanced AMD. We reinforce the concept of maculoplasty for advanced AMD, which is defined as reconstruction of macular anatomy in patients with advanced vision loss. Successful maculoplasty is a three-step process that includes replacing or repairing damaged cells (using transplantation, translocation or stimulation of autologous cell proliferation); immune suppression (if allografts are used to replace damaged cells); and reconstruction or replacement of Bruch's membrane (to restore the integrity of the substrate for proper cell attachment).

In the current article we will review the rationale for maculoplasty in advanced AMD, and discuss the results of initial clinical attempts at macular reconstruction. We will then discuss the role of Bruch's membrane damage in limiting transplant survival and visual recovery, and discuss the effects of age-related changes within human Bruch's membrane on the initial attachment and subsequent proliferation of transplanted cells. We will discuss attempts to repair Bruch's membrane by coating with extracellular matrix ligands, anatomic reconstitution of the inner collagen layer, and the effects of Bruch's membrane reconstruction of ultrastuctural anatomy and subsequent cell behavior. Lastly, we will emphasize the importance of continued efforts required for successful maculoplasty.     

Characteristics of drusen and Bruch's membrane in post-mortem eyes with age-related macular degeneration

Background: Different types of drusen and changes in Bruch's membrane have been associated with age-related macular degeneration (AMD). Methods: We compared 51 eyes with different stages of AMD with 40 age-matched controls using light microscopy. The degree of calcification of Bruch's membrane, fragmentation of Bruch's membrane, number of different types of drusen, and basal laminar deposit (BLD) were assessed. Results: In the macular area, the presence of basal laminar deposit was most strongly associated with the presence of AMD. There was a statistically significant difference observed in the degree of calcification and fragmentation of Bruch's membrane in eyes with AMD as compared to controls. Eyes with AMD displayed significantly more soft, confluent, and large drusen as compared to controls. Conclusion: Calcification and fragmentation of Bruch's membrane, soft, confluent, and large drusen and BLD but not hard drusen correlated strongly with the histologic presence of AMD. Calcification and fragmentation of Bruch's membrane seem to facilitate ingrowth of choroidal neovascular membranes with consecutive development of exudative AMD.      

Bruch's membrane age-related changes vary by region

Aging changes known to occur in Bruch's membrane may be associated with drusen formation and retinal pigment epithelial mottling, which often have a peripheral as well as a macular distribution. Few details of peripheral Bruch's membrane aging changes have been reported. We conducted a histochemical investigation of Bruch's membrane in 31 postmortem donor eyes and an ultrastructural morphometric investigation of these regional changes in a subgroup of 22 eyes. The age of our donors ranged from 12 days to 80 years. When we reacted 5 micron paraffin embedded sections of chorio-retinal complex fixed in 2% glutaraldehyde-1% paraformaldehyde, we observed increased PAS positivity, and staining with Weigert's elastin and alcian blue at pH 2.5 in Bruch's membranes from donors over 46 years. In this older group, the macula showed increased histochemical reactivity for glycoconjugates, glycosaminoglycans, collagen and elastin as compared with the equator and periphery. Thickening of Bruch's membrane was first detected in the periphery in tissue from donors aged 10 to 45. Thickening of macular Bruch's membrane was first detected in tissue from donors older than 45. The major proportion of thickening, which appears to be due to the deposition of fibrillar and amorphous material, occurred earlier in the inner than the outer collagenous zone. The equatorial region was relatively spared. Our findings confirm and extend the observations of the timing, regional predeliction, and extent of Bruch's membrane aging changes.     

Macromolecular diffusion characteristics of ageing human Bruch's membrane: Implications for age-related macular degeneration (AMD)

Macromolecular species such as retinal binding protein, transferrin, ceruloplasmin, etc., released by the fenestrated choroidal capillaries must diffuse across Bruch's membrane for interaction with the basal membranes of the retinal pigment epithelium (RPE) for delivery of essential metabolites to the neural retina. The patency of this pathway through ageing Bruch's was examined by quantifying the diffusional flux of a 21.2 kDa fluorescein-isothiocyanate labelled dextran. Dextran flux measurements across Bruch's membrane from the macular region of the human fundus showed a highly significant decrease (p < 0.001) with ageing of donor such that diffusional transport in the ninth decade was about 6.5% of that in the first decade of life. Peripheral regions also showed a highly significant decline (p < 0.001) but ageing changes were considerably slowed in comparison to the macula with diffusional rates in the ninth decade being about 44% of that in the first decade. Peripheral samples from AMD donors displayed diffusional rates that were lower than the control population. The age-related decline in macromolecular diffusion across Bruch's membrane suggests that in the elderly, the patency of the conducting pathways may be compromised and in the more advanced ageing of Bruch's associated with AMD, the metabolic trafficking of carrier proteins may be severely impaired.     

Morphometric analysis of lipoprotein-like particle accumulation in aging human macular Bruch's membrane

PURPOSE: To determine the size and regional distribution of lipoprotein-like particles (LLPs) that accumulate with age in Bruch's membrane (BrM). METHODS: The quick-freeze/deep-etch method was used to prepare specimens of human BrM (age range, 27-78) for electron microscopic examination. Stereologic methods were used to analyze the resultant micrographs and determine the age-related changes of the LLP volume fraction and diameter distribution in various locations in BrM. RESULTS: The volume fraction occupied by LLPs was found to increase monotonically with age in both the inner collagenous layer (ICL) and elastic layer (EL), but not in the outer collagenous layer (OCL). The mass of total LLP-associated lipids in BrM also increased with age. There was no significant increase in LLP size with age, but there was a modest increase in size with increased volume fraction of LLPs in BrM. CONCLUSIONS: The pattern of accumulation of particles was consistent with a retinal pigment epithelium (RPE) source for the LLPs, which explains why once the EL and ICL were filled with particles, LLPs continued to accumulate near the RPE, but no further accumulation was found in the OCL. The quantity of LLP-associated lipids found in BrM accounts for a large portion of the accumulated lipids measured in this tissue.     

VEGF in age-related macular degeneration. Part II. VEGF inhibitors use in age-related macular degeneration treatment

Wet AMD remains a therapeutic challenge. VEGF inhibitors are new promising group of medical agents undergoing advanced clinical trials. Oncology is the main specialty using anti-VEGF therapy. Two agents were designed from the beginning as ophthalmologic medicines. These are pegaptanib and ranibizumab. In the paper there is mechanism, efficacy and safety data presented, especially coming from multi-center randomized clinical trials. Monoclonal VEGF-antibodies (ranibizumab and bevacizumab) seem to be most effective in wet AMD treatment. Because of important physiological VEGF role long-term observation is needed to confirm safety of VEGF inhibition.     

Deficits in the electroretinogram in neovascular age-related macular degeneration and changes during photodynamic therapy

Purpose To describe the deficits in four electroretinography (ERG) modalities in patients with neovascular age-related macular degeneration (AMD). To describe the changes in these parameters during a course of verteporfin photodynamic therapy (PDT). Methods Pattern (PERG), multifocal (mfERG) (19 segment simplified test protocol), flash ERG and flicker ERG were performed in patients with active neovascular AMD before PDT and compared to fellow eye controls using paired t-tests. Changes in ERG parameters during the 12 month treatment course were visualised using 95% confidence intervals of the median difference. The statistical significance of any changes was quantified using Wilcoxon signed ranks tests. Results Fifty patients were recruited and followed. At presentation all ERG amplitudes were reduced with greater reductions in focal as opposed to global test protocols (P < 0.05). Over the 12 month course of PDT, PERG P50 amplitude showed a general downward trend and latency remained unchanged. mfERG p1 amplitude density showed an upward trend at six months before returning to baseline by 12 months. mfERG ring 2 amplitude density was significantly increased at 12 months compared to baseline (P = 0.010). Flicker ERG latency was significantly increased at six months compared to baseline (P = 0.015). Discussion The simplified mfERG protocol was tolerated by this patient group, however, they found the full test protocol demanding. Large deficits in the retinal ERG function occur in neovascular AMD and involve retinal locations adjacent to as well as overlying choroidal neovascularisation (CNV). After PDT there is an improvement in electro-retinal function in retinal locations overlying the CNV.     

年龄相关性黄斑变性黄斑部循环改变与脉络膜新生血管形成

目的探讨年龄相关性黄斑变性(age-relatedmaculardegeneration,AMD)黄斑部循环改变与脉络膜新生血管(choroidalneovascularization,CNV)形成的关系。方法对12例(24眼)首诊为萎缩型AMD,在随访中转变为渗出型AMD(16眼)的眼底荧光素血管造影(fundusfluorescenceangiography,FFA)及吲哚青绿血管造影(indocyaninegreenangiography,ICGA)图像进行回顾性分析,对比观察脉络膜循环变化。结果24只萎缩型AMD黄斑区脉络膜毛细血管层均有局限性灌注不良,16眼(67%)CNV在原脉络膜毛细血管灌注不良区域内生成。结论脉络膜灌注不良是CNV形成的主要原因。     

TLR3与年龄相关性黄斑变性疾病的相关性

年龄相关性黄斑变性(age-related macular degeneration, ARMD)是一种多发于50岁以上人群的慢性进展性疾病, 是发达国家老年人群的主要致盲性眼病,也是发展中国家老年人群不可逆视力损害的主要原因, ARMD包括地图状萎缩及脉络膜新生血管两类。由于其具体病因和发病机制尚不明确, 大多数学者认为这是一种多因素疾病。近年来Toll样受体3(Toll-like receptor 3,TLR3)与ARMD关系的研究成为热点,本文就近年来相关研究进展做一综述。     

Associations of plasma-soluble fas ligand with aging and age-related macular degeneration

PURPOSE: To evaluate the associations between plasma-soluble Fas ligand (sFasL) and age-related macular degeneration (AMD). METHODS: Plasma samples were obtained from 230 individuals (age range, 45-85), with or without AMD. The concentrations of sFasL were determined by an enzyme-linked immunosorbent assay (ELISA). The measured sFasL levels were transformed into cubic roots and were fitted into linear regression models against AMD status, with adjustment for age and sex. RESULTS: Plasma sFasL increased with age and AMD. There was a linear correlation between age and the cubic roots of sFasL. The plasma sFasL concentrations in non-AMD subjects ranged from 0 to 1.63 ng/mL (median, 0.69 ng/mL), whereas in patients with AMD, sFasL ranged from 0 to 2.43 ng/mL (median, 0.18 ng/mL). Between the ages of 61 and 84, the subjects with AMD had significantly higher sFasL than did the non-AMD subjects. There was a sexual dimorphism of the plasma sFasL levels. In non-AMD subjects, sFasL was lower in the females. In patients with AMD, sFasL was higher in the females. CONCLUSIONS: An elevation of plasma sFasL with aging may play a role in the development of AMD and is a potential peripheral marker for monitoring disease progression.     

Preparation of Bruch's membrane and analysis of the age-related changes in the structural collagens.

AIMS/BACKGROUND--The morphological changes in Bruch's membrane and its constituent collagen seen during aging have been studied extensively but the chemical nature of the collagen and any aging changes have not previously been evaluated. METHODS--A method for preparing purified Bruch's membrane from human cadaver eyes by dissection preceded by trypsin digestion was developed. Following pepsin digestion, the constituent collagens were analysed by SDS-PAGE and by immunoblotting. Cyanogen bromide digestion was used to ascertain the solubility of the collagen and the proportion of type I to type III collagen. After hydrolysis of Bruch's membrane samples the constituent amino acids and collagen crosslinks were measured. RESULTS--The presence of collagen types I, III, IV, and V in Bruch's membrane was confirmed. The proportion of type III collagen as a percentage of total fibrous collagens was calculated as being between 35% and 39%, with no significant difference between different macular and peripheral sites or with age. There was a highly significant decline in the solubility of Bruch's membrane collagen with age, from near 100% in the first decade of life to 40-50% in the ninth decade at both macular and peripheral sites. There was no significant change in the amount of enzymatically formed collagen crosslinks with age. Amino acid analysis indicated a significant increase in the amount of non-collagen protein with age in macular but not peripheral sites. CONCLUSION--Changes in the constituent collagens may contribute to the accumulation of debris in Bruch's membrane with age and interfere with the function of the retinal pigment epithelium, with subsequent consequences for the overlying photoreceptors.     

Drusen in Bruch's membrane. Their significance for the pathogenesis and therapy of age-associated macular degeneration]

The drusen found in Bruch's membrane represent precursors for the development of age-related macular degeneration. The pathogenetic concepts are summarized: 1. As a result of aging changes in the metabolism of the pigment epithelium with age, the normal structure of Bruch's membrane is destroyed. This process is associated with lipid accumulation and the development of drusen. The lipids deposited are predominantly phospholipids or neutral lipids. 2. The clinical appearance of drusen can also vary from one person to another, but individually a significant symmetry of drusen characteristics can be seen, demonstrating that drusen are the results of specific metabolic dysfunctions rather than non-specific aging products. 3. The development of specific forms of age-related macular degeneration corresponds with different drusen. Larger, more confluent and hypofluorescent drusen are associated with the development of pigment epithelium detachments. In eyes with smaller, scattered and hyperfluorescent drusen, choroidal neovascularizations are more likely. 4. Histochemically, larger, hypofluorescent drusen contain predominantly neutral lipids. In contrast, smaller, hyperfluorescent drusen consist predominantly of phospholipids. 5. The accumulation of neutral lipids in Bruch's membrane is therefore associated with Pigment epithelium detachments. These apolar lipids may produce a hydrophobic barrier in Bruch's membrane for the water transport from the retina towards the choroid. A pigment epithelium detachment can develop. 6. The deposition of polar phospholipids predisposes to the development of choroidal neovascularization. These lipids in association with the changed structure of Bruch's membrane may induce an inflammation--like reaction, resulting in the in-growth of choroidal capillaries under the pigment epithelium. The analysis of the relationship between subclinical aging changes in Bruch's membrane and different forms of age-related macular degeneration may help to identify specific risk factors and to predict the future outcome in individual eyes. This may result in differentiated treatment concepts adapted to the specific aging changes in each person.