Pathophysiology of age-related macular degeneration

Drusen as risk factors in age-related macular disease

In a study of 150 consecutive patients with age-related macular disease and unilateral visual loss, the drusen in the better eye were analyzed for size, number, density, and fluorescein angiographic appearance, and these characteristics were compared with the type of the lesion causing visual loss in the contralateral eye. In the fellow eye of an eye with avascular detachment of the retinal pigment epithelium, the drusen were more densely packed, larger, and less fluorescent than in the fellow eye of an eye with primary neovascularization. The characteristics of drusen in fellow eyes of those eyes with pigment epithelial detachments and evidence of subpigment epithelial new vessels were intermediate between the other two groups. Because there is significant symmetry of drusen between fellow eyes, these data imply that the characteristics of drusen are important in the determination of the form of the lesion complicating age-related macular disease.

Rheological studies on patients with posterior subretinal neovascularization and exudative age-related macular degeneration

To investigate the potential influence of a decreased perfusion rate of the choriocapillaris on the development of age-related macular degeneration (ARMD) with subretinal neovascularization (SRNV) apparently caused by disturbed flow properties of blood, we compared the hemorheological parameters of blood from 35 patients suffering from ARMD with SRNV with those from the 35 healthy patients of the same age. In both groups hematocrit, plasma viscosity, erythrocyte filtrability, aggregation, aggregating proteins, leukocyte and thrombocyte count, differentiation of leukocytes, thrombelastography, PTT, Quick test, and rheological profiles were comparable. The differences were not significant (P greater than 0.05). These results refute the hypothesis that changed flow properties of blood are the primary cause of the pathogenesis of ARMD with SRNV.

Autoantibodies to retinal astrocytes associated with age-related macular degeneration

Sera from 128 patients with age-related macular degeneration (AMD) were examined and profiles of a variety of serum constituents, including immunoglobulins, alpha and beta globulins and autoantibodies, were tabulated. A similar series of tests were carried out on 20 control sera. The results indicate a higher incidence of serum abnormalities, particularly involving alpha-2 globulin, in patients with disturbance of pigmentation of the retinal pigment epithelium (RPE). The sera were further tested for the presence of autoantibodies with specificity for retinal tissue, and five major staining patterns were observed. Many sera produced patterns of labelling on human retina identical to that observed using labelled monoclonal anti-glial fibrillary acid protein (GFAP) antibodies, which are an established marker of retinal astrocytes. Although anti-retinal autoantibodies have been reported in association with a number of ocular pathologies, the observation of anti-astrocyte autoantibodies is new. Astrocytes are involved in the maintenance of the blood-retinal barrier (BRB) and also appear to be the facultative antigen-presenting cells of neural tissue. The present results indicate that the formation of anti-astrocyte autoantibodies may be an early feature of the pathogenesis of AMD.

Study of human epithelial cell detachment and damage: development of a model

Detachment of epithelial structures from underlying basement membrane (BM) represents an important component of a number of human disease processes e.g. airway and alveolar diseases, gastrointestinal ulceration, and retinal diseases. This study describes a method of evaluating human epithelial cell detachment from BM that is simple, rapid, inexpensive, quantifiable and which, because it utilizes BM rather than tissue culture plastic, more closely mimics the in vivo situation than other methods. In this model human amnionic epithelial cells attached to their underlying BM are isolated from fresh placentae and mounted in a multi-well chemotaxis assembly. These membranes can be studied with the epithelial cell monolayer intact. Protease-induced detachment of the epithelial cells from the underlying BM was readily quantifiable using light microscopy and spectroscopy. Following removal of the native amnionic epithelial cells, immunoperoxidase staining for the BM attachment proteins laminin, fibronectin, and type IV collagen demonstrated that these molecules remain intact. The BM could also be used as an attachment surface to reconstitute other epithelial cell monolayers. Cultured human amnionic cells and human respiratory epithelial cells were both able to attach to the denuded BM in the absence of serum (% attachment = 85 +/- 15% and 92 +/- 8% respectively, P = 0.8). Natural BM was a better substrate for epithelial cell attachment than tissue culture plastic in that, in the absence of serum, cultured epithelial cell attachment to tissue culture plastic was 20 +/- 4% of the value for BM (P less than 0.05). Furthermore, cells attached to plastic adhered less effectively than to BM in that trypsin concentrations required to induce 50% cell detachment were 0.72 +/- 0.4 for plastic and 62 +/- 13 BAEE U/ml for BM (P less than 0.001). In view of the complex protein interactions known to be involved in the anchorage of human epithelial cells to BM, it is likely this model will be a useful tool for evaluating the mechanisms underlying human epithelial cell attachment and detachment in a variety of normal and disease situations.

Age-related macular degeneration. Macular changes, prevalence and sex ratio. An epidemiological study of 1000 aged individuals

An epidemiological ophthalmic investigation of 1000 individuals aged 60-80 years disclosed age-related macular degeneration (AMD), i.e. macular changes causing visual impairment in at least one eye with a prevalence of 12.2% of 924 individuals with both maculae examined. The prevalence increased with rising age for both sexes: age group 60-64 years: 2.3%, 65-69: 5.9%, 70-74: 12.1% and 75-80: 27.3%. No significant differences in prevalence rates of AMD were demonstrated between males and females in the respective age groups. About one half of the persons with AMD were affected in both eyes. No differences of AMD were found between right and left eyes. Findings of age related macular changes without visual impairment (AMCW) compared to AMD revealed far higher prevalences in the sixties and a smaller rise in the seventies (age group percentage in both sexes: 12.3, 18.0, 17.0 and 17.8%). No systematic prevalence differences were demonstrated between sexes. The collected data of AMD and AMCW might indicate a shift from AMCW to AMD in women, particularly aged 70-74 years and in men, particularly aged 75-80 years. Macular changes in total (AMD + AMCW) was found in 28.5% of the population (age group percentage 14.6, 23.8, 29.0 and 45.0%). No sex differences were found.

Atrophic macular degeneration. Rate of spread of geographic atrophy and visual loss

The authors studied 50 eyes with atrophic (dry) macular degeneration (geographic atrophy of age-related macular degeneration [GAMD], in 50 consecutive patients for 2 to 6 years (average, 3.4 years). There were 35 women and 15 men ranging in age from 60 to 89 years (average, 73 years). The areas of atrophy tended to follow the disappearance or flattening of soft drusen, pigment epithelial detachment, or reticular mottling of the retinal pigment epithelium. The atrophic areas were multifocal in 20 of the 50 eyes. Atrophy of the retinal pigment epithelium was followed by atrophy of the choriocapillaris. The atrophic areas tended to expand (average rate in one direction, 139 microns per year) and cause gradual loss of central visual acuity. The rate of significant visual loss (from 20/50 or better to 20/100 or worse) was 8% of eyes per year. There was a tendency toward resistance of the spread of atrophy into the fovea. The atrophy tended to expand faster in patients under age 75 and slower in patients aged 75 and over. Subretinal neovascularization developed in ten of the 50 eyes.

Evolution of geographic atrophy of the retinal pigment epithelium

The aim of this study was to trace the evolution of geographic atrophy (GA) by clinical documentation and by clinico-morphological correlation in representative eyes. Geographic atrophy commonly commenced within a parafoveal band of incipient atrophy of varying width, characterised by semisolid drusen and a microreticular pigment pattern. Progression of atrophy mostly skirted fixation and visual acuity was a poor guide to the functional impact, an estimate of the percentage of fovea involved proving a more useful clinical parameter. The rate of progression slowed once GA had involved all the retina affected by incipient atrophy and the risk of choroidal neovascularization appeared to decline. An earlier histological classification of the evolution of GA is revised according to the ultrastructural findings. Membranous debris was not previously recognised and its contribution to the findings in incipient atrophy and to dot-like drusen is described.

Retinal pigment epithelial cell plasma membrane: a monoclonal antibody study

The plasma membranes of retinal pigment epithelial cells are highly specialized organelles with multiple functions including nutritional and metabolic support of the photoreceptor cells. Using purified bovine retinal epithelial cell plasma membranes as antigen, we produced two monoclonal antibodies, MAbD1-C6 and MAbD1-C8, that cross react with the plasma membranes from bovine, rat and human retinal pigment epithelial cells. In radioimmunoassay both MAbD1-C6 and MAbD1-C8 had similar affinities for bovine plasma membranes. Both monoclonal antibodies identified a protein of 72 Kd with an apparent subunit of 32-35 Kd. The protein was localized to the cell surface of human and bovine retinal pigment epithelium by immunocytohistochemistry. In the normal eye the antigen identified by the monoclonal antibodies was strongly associated with the retinal pigment epithelium and weakly associated with lens tissue. Using either monoclonal antibody, components of purified bovine or rat retinal pigment epithelial plasma membranes were precipitated from solution. Based on these results, we conclude that both monoclonal antibodies are closely related and that they may be useful for the isolation and study of retinal pigment epithelial cell structure.

Age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible severe visual loss in the United States in people over 50 years of age. The nonexudative stage includes hard drusen (associated with localized dysfunction of the retinal pigment epithelium [RPE]), soft drusen (associated with diffuse dysfunction of the RPE), and geographic (areolar) atrophy. These fundus changes may predispose the eye to develop the neovascular/exudative stages of AMD. Most patients who develop severe visual loss from AMD have this exudative stage. Treatment for AMD has been shown to be effective for only a small proportion of patients who have a well-defined choroidal neovascular membrane (CNVM) more than 200 microns from the foveal center. Even in successfully treated cases, severe visual loss is postponed only for about 18 months because of the high rate of recurrent CNVMs that extend into the fovea. Thus, despite recent breakthroughs in laser treatment for AMD, most patients who develop the exudative form of AMD will develop central visual impairment. At the present time, the only available treatments for the majority of patients who develop the exudative form of AMD are low vision aids. Investigators are currently evaluating whether treatment is effective for membranes within 200 microns of the foveal center. Future studies need to be directed toward further understanding of the pathogenesis, treatment and prevention of the blinding complications of AMD.

Solar radiation and age-related macular degeneration

Age-related macular degeneration (AMD) involves a progressive impairment of the outer layers in the center of the retina. Experimental studies have demonstrated that bright light preferentially damages precisely the region that degenerates in AMD. The evidence that solar radiation is responsible for some of the deteriorative changes that lead to AMD is examined in this review. In the primate eye, the high-energy portion of the solar spectrum is most hazardous to retinal molecules, with damaging effects increasing as photon energy rises. This action spectrum is explicable by the quantum laws which describe the interaction of radiation with matter. High-energy visible and ultraviolet photons can produce molecular damage by a photochemical mechanism. The lesion is exacerbated by oxygen, which initiates free-radical chain reactions (photodynamic effects). Melanin exerts a protective effect against damage from sunlight. In the human retina, documented lesions from solar radiation range from the acute effects of sun-gazing to injuries resulting from prolonged periods of exposure in brightly illuminated environments. The damage occurs in the same region that degenerates in AMD. A cataractous lens and ocular melanin both protect the retina against AMD, as predicted by the radiation hypothesis. Identification of an environmental factor that evidently plays a role in the etiology of AMD provides the basis for a program of preventive medicine.