Cone degeneration in aging and age-related macular degeneration.

OBJECTIVE: To examine the morphological features of macular photoreceptors in histologically normal retina from normal donor eyes and eyes with age-related macular degeneration (AMD). METHODS: The macular region was excised from 18 donor eyes (aged 22-96 years) and cryosectioned. Sections were stained with hematoxylin-eosin or double immunolabeled using opsin antibodies or synaptic markers. RESULTS: Three of 8 retinas studied in detail had AMD lesions; the remainder were histologically normal. Immunoreactivity to cone opsin was abnormal in parts of all retinas (3.5%-95.0% of each sample) and was associated with swelling of and altered immunoreactivity in the cone distal axon. In non-AMD retinas, the anomalies were mainly in nonfoveal macular locations. The nature of the anomalies was identical in non-AMD retinas and in parts of AMD retinas adjacent to overt degeneration. CONCLUSION: Redistribution of opsin and anomalies in the distal cone axon are common in the aging human macula and may indicate susceptibility to AMD. CLINICAL RELEVANCE: The findings are consistent with tests of cone function in aging and early AMD, which suggests that integrated cone functions--including contrast sensitivity, color matching, and short wavelength-sensitive cone sensitivity--are the most reliable prognostic indicators of progression in AMD.

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.

Immunoglobulin superfamily expression in primary retinoblastoma and retinoblastoma cell lines.

Retinoblastoma (Rb) is the most common intraocular tumor of childhood. In this study we examined primary Rb specimens and Rb cell lines for the expression of immunoglobulin superfamily (IgSF) antigens: MHC class I and II (MHC-I and MHC-II), neural cell adhesion molecule (NCAM), intercellular adhesion molecule-1 (ICAM-1), and Thy-1, which play an important role in immune system and tumor cell interactions. MHC-I and-II, ICAM-1 (CD54), NCAM (CD56), and Thy-1 (CDw90) immunoreactivity was studied in eight primary Rb biopsy specimens using immunohistochemistry, three using immunoelectron microscopy, and six Rb cell lines using flow cytometry (FCM). Parenchymal and vascular-associated cells, phenotypically similar to retinal microglia, strongly expressed MHC-II immunoreactivity and were distributed throughout primary Rb specimens. However, MHC-II expression on Rb cell lines was similar to nonspecific control levels. Tumor cells in primary Rb specimens displayed high NCAM, moderate Thy-1, and low MHC-I and ICAM-1 immunolabeling. Tumor vasculature expressed low to moderate MHC-I and ICAM-1 immunoreactivity and moderate Thy-1 immunoreactivity. NCAM was not detected on the vasculature of primary Rb specimens. Rb cell lines displayed variable expression of Thy-1, ICAM-1, and MHC-I. NCAM was highly expressed on five of six Rb cell lines. The high levels of constitutive NCAM immunoreactivity on Rb tumor cells confirm the neuroectodermal origins of this tumor. Additionally, the variable expression of Thy-1 may suggest separate neural lineages or differences in the maturational status ofsome Rb tumors. The presence of a population of infiltrating MHC-II-positive cells in primary Rb tumors has implications for immunomodulation of Rb growth.

Modulation of permeability and adhesion molecule expression by human choroidal endothelial cells.

PURPOSE: The therapeutic potential of TA, an anti-inflammatory glucocorticoid, for the treatment of exudative retinopathy has been examined in several independent clinical studies. The modulation of permeability and adhesion molecule expression of an epithelial cell line has been described in vitro, with the use of cytokines and triamcinolone acetonide (TA). In the current study, the influence of proinflammatory cytokines and TA on permeability and adhesion molecule expression in human choroidal endothelial cells (CECs) was investigated. METHODS: Human CEC isolates treated with IFNgamma, TNFalpha, and TA were evaluated by flow cytometry and immunocytochemistry for expression of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and major histocompatibility complex (MHC)-I and -II. The effects of IFNgamma, TNFalpha, and TA on paracellular permeability of CEC monolayers were assessed in transendothelial cell resistance (TER) assays. RESULTS: Both IFNgamma and TNFalpha significantly upregulated expression of ICAM1 and MHC-I on CECs. Expression of VCAM1 was induced after stimulation with both IFNgamma and TNFalpha, whereas expression of MHC-II was induced only by stimulation with IFNgamma. Cytokine-induced expression of ICAM1, MHC-I, and MHC-II antigen by CECs was significantly downregulated by TA. IFNgamma stimulation also increased permeability of CEC monolayers, whereas subsequent TA treatment decreased permeability of CEC monolayers. CONCLUSIONS: Human CEC isolates provide a useful in vitro model to study choroidal neovascular membrane characteristics and their potential response to pro- and anti-inflammatory agents. In addition, the results indicate that TA has the capacity to reduce adhesion molecule expression and permeability of choroidal vessels in vitro, confirming its potential as a therapeutic agent for treatment of exudative macular degeneration.

Effects of post-mortem delay and storage duration on the expression of GFAP in normal human adult retinae.

Glial fibrillary acidic protein (GFAP) is an established marker of retinal glia and has been shown to be modulated by several cytokines and retinal pathology. The influence of a number of factors, including post-mortem delay, storage duration and retinal pathology, on the distribution and morphology of macroglia and GFAP antigenicity was examined in human retina. The effects of these parameters on GFAP expression were estimated using immunohistochemistry, confocal microscopy and image analysis. Changes in expression of antigenicity were analysed in human retinal cryosections at three levels: constitutive,aberrant and total. The results indicated that short-term and long-term storage duration had no significant effect on GFAP immunoreactivity at all three levels of expression (P > 0.2).However, a significant increase in GFAP immunoreactivity and distribution at all three levels of expression was associated with prolonged post-mortem delay (> 30 h) (P < 0.05). This study highlights the importance of rigorous matching of post-mortem delay between control specimens in histological studies of human retinae. The study further demonstrates the utility of Eye Bank retinae fixed and stored in 2% paraformaldehyde, provided that appropriate controls are applied.