Risk factors in age-related maculopathy complicated by choroidal neovascularization

Antioxidants and age-related eye disease. Current and future perspectives

Oxidative mechanisms may play an important role in the pathogenesis of age-related eye disease, in particular cataract and macular degeneration, the two most important causes of visual impairment in older adults. For this reason, there is considerable interest in determining whether vitamins and trace minerals with antioxidant properties can be of benefit in preventing the onset or progression of disabling eye disease. Basic research studies have shown that antioxidants can protect against the cumulative effects of oxidative stress in animal models of cataract and macular degeneration. Data from observational epidemiological studies in humans, however, are inconclusive. While results from several studies, primarily cross-sectional and case-control, are compatible with a possible protective role for micronutrients in disease development, data for specific nutrients or specific disease types have often been inconsistent. Further, these observational studies are limited because of the inherent imprecision of dietary exposure data and the likely effects of uncontrolled confounding. Thus, reliable data regarding a potentially important benefit of vitamin supplementation in eye disease will emerge mainly from well-designed, large-scale, randomized trials.

The Nambour study of ocular disease. I. Design, study population and methodology

In association with a study of actinic skin disease, we undertook a comprehensive survey of ocular disease in a population sample of the town of Nambour, Queensland, Australia. Particular emphasis was placed on those diseases with a putative relationship to exposure to solar radiation. In addition to collecting prevalence data, a randomized controlled trial was commenced to determine, among other things, if daily ingestion of 30 mg of beta-carotene supplements reduces the incidence or progression of ocular diseases possibly related to solar radiation exposure. The study design, population and methodology of the study are described in detail as a background to the future reporting of the results. The study should provide unique epidemiological information about eye disease in an Australian community setting due to the representative nature of the subjects and the comprehensive examination performed.

A twin study of age-related macular degeneration

PURPOSE

To determine the importance of genetic factors in age-related macular degeneration by using a twin study to compare the concordance of age-related macular degeneration in monozygotic and dizygotic twin pairs.

METHODS

We prospectively examined 134 consecutive twin pairs and two triplet sets for age-related macular degeneration. The zygosity was determined by genetic laboratory tests.

RESULTS

The concordance of age-related macular degeneration was 100% (25 of 25) in monozygotic and 42% (five of 12) in dizygotic twin pairs. The other twins or triplets had no macular changes of age-related macular degeneration.

CONCLUSIONS

The statistically significant higher concordance of age-related macular degeneration in monozygotic than in dizygotic twin pairs and the clinical heterogeneity of age-related macular degeneration strongly suggest the importance of genetic and nongenetic factors, respectively, in age-related macular degeneration.

Preventative ophthalmology. Age-related macular degeneration

PURPOSE

This report was designed to review the current knowledge about preventing the development or progression of age-related macular degeneration (AMD) and visual loss associated with this entity in practical terms for the comprehensive ophthalmologist.

METHODS

Animal studies, epidemiologic studies, and clinical trials identified through the use of MEDLINE, a reference list of articles reviewed, and personal contact with experts in this area provided information reviewed for this report.

RESULTS

Reports concerning ultraviolet and visible light provide limited, inconsistent, and conflicting data to support the theory that light exposure leads to AMD. Micronutrient supplementation is a provocative but largely unproven hypothesis. Positive associations of cigarette smoking and cardiovascular disease or certain risk factors for cardiovascular disease with AMD provide potential clues as to the underlying pathogenesis of AMD and are yet another reason to treat these health problems. Drusen may disappear after laser to the macula; however, this intervention will require careful, randomized, prospective trials to determine if this therapy can reduce the risk of choroidal neovascularization and visual loss developing in patients with AMD.

CONCLUSIONS

It is reasonable to have individuals wear sunglasses for comfort and possible protection from ultraviolet light exposure to all ocular structures (especially the lens) at little or no risk to the patient. Physicians probably should be reluctant to prescribe micronutrients or suggest other interventions (such as laser to drusen) until their health claims have been substantiated and their long-term safety soundly established.

Asymmetry of disciform scarring in bilateral disease when one eye is treated with radiotherapy

AIMS/BACKGROUND

A previous study has shown that in age-related macular degeneration a high degree of concordance of disciform scar size occurs in the two eyes of any one patient. In a study of 35 patients with choroidal neovascular membrane who were treated with low dose ionising radiation to the macula of the affected eye, 11 were found to have bilateral disease.

METHODS

The visual outcome and scar size and morphology in the two eyes of each of these patients were compared.

RESULTS

In all radiotherapy treated eyes the appearance of the scar ranged from subtle subretinal pigmentary changes to dense subretinal fibrosis. By contrast all untreated fellow eyes showed marked subretinal scarring. Scars in radiotherapy treated eyes occupied an area that was approximately one third of that in untreated fellow eyes (3.8 mm2 v 11.7 mm2). Distance and near visual acuities in radiotherapy treated eyes were significantly better than that of untreated fellow eyes (p < 0.0033). Although untreated fellow eyes of necessity had longer follow up periods (64.5 months), the mean follow up time in treated eyes was 28 months by which time the disciform response is generally thought to have ceased evolving.

CONCLUSION

This study has provided evidence in support of reduced scarring and maintenance of better central visual function in radiotherapy treated eyes when compared with untreated fellow eyes.

The health effects of vitamin C supplementation: a review

A comprehensive review of the literature indicates that populations with long-term consumption of higher than RDA levels of vitamin C (> or = 60 mg/day) from foods and/or supplements have reduced risks of cancer at several sites, cardiovascular disease, and cataracts. The safety of higher than RDA intakes of vitamin C is confirmed in eight placebo-controlled, double-blind studies and six non-placebo clinical trials in which up to 10,000 mg of vitamin C was consumed daily for up to 3 years. There are no clinical data which suggest that vitamin C's enhancement of non-heme iron absorption in individuals with low iron status could be a critical factor in the possible increased risk of heterozygous hemochromatosis-related cardiovascular disease. In fact, the cumulative data do not confirm that iron status is related to risk of cardiovascular disease. Moreover, higher than RDA intakes of vitamin C have been associated with several indices of lowered cardiovascular disease risk including increases in HDL, and decreases in LDL oxidation, blood pressure and cardiovascular mortality.

Antioxidants and eye disease

Oxidative mechanisms are believed to play an important role in the pathogenesis of age-related eye disease, in particular, cataract and macular degeneration, the two most important causes of visual impairment in older adults. For this reason, there is considerable interest in determining whether vitamins and trace minerals with antioxidant properties can be of benefit in preventing the onset or progression of disabling eye disease. Basic research studies have shown that antioxidants can protect against the cumulative effects of oxidative stress in animal models of cataract and macular degeneration. Data from observational epidemiologic studies in humans, however, are inconclusive. While results from several studies, primarily cross-sectional and case-control, are compatible with a possible protective role for micronutrients in cataract and macular degeneration, data for specific nutrients or specific disease types have often been inconsistent. Further, these observational studies are limited because of the inherent imprecision of dietary exposure data and the likely effects of uncontrolled confounding. Thus, reliable data regarding a potentially important benefit of vitamin supplementation in eye disease will emerge mainly from well-designed, large-scale, randomized trials. Such data are already being collected in the National Eye Institute-sponsored Age Related Eye Disease Study, as well as in the Physicians' Health Study and Women's Health Study.

Decreasing stromal iris pigmentation as a risk factor for age-related macular degeneration

To evaluate iris color, change of iris color, and iris pigment epithelial defects as risk factors in age-related macular degeneration, we compared 101 patients with age-related macular changes with 102 control subjects in a case-control study. Three of 101 patients (3%) and four of 102 control subjects (4%) had epithelial iris defects. Light iris color during youth was reported by 51 of 101 patients (50.5%) and 42 of 102 control subjects (41.2%) (odds ratio, 1.46; P = .184). Of the 101 patients, 26 (25.7%) noticed their iris color to have become lighter during life compared with six of 102 control subjects (5.9%) (odds ratio, 5.5; P = .0001). At present examination, 63 of 101 patients (62.4%) had light irides compared with 43 of 102 control subjects (42.2%) (odds ratio, 2.27; P = .004). These results suggest that initial light iris color and iris pigment epithelial defects are not associated with an increased risk of age-related macular degeneration, whereas decreased stromal iris pigmentation may indicate a higher risk.

Age-related macular degeneration

Age-related macular degeneration (AMD), a bilateral, progressive macular disease, represents the major cause of blindness among elderly people living in Western countries. Clinical features of AMD vary from the initial asymptomatic aspects, drusen and retinal pigment epithelium alterations, to severe atrophic or exudative changes in the advanced stages, characterized by the irreversible decrease of visual function. Current epidemiologic, pathogenetic and clinical data are reviewed, and the importance of the exact identification of patients at risk of evolution toward the exudative form is addressed. The therapeutic approach to AMD is also analyzed and the role of laser photocoagulation is discussed.

The relationship of cardiovascular disease and its risk factors to age-related maculopathy. The Beaver Dam Eye Study

PURPOSE

To examine the association between cardiovascular disease and its risk factors to age-related maculopathy in a population-based study of people between the ages of 43 and 86 years (n = 4926) between 1988 and 1990.

METHODS

Population-based prevalence study using standardized protocols for physical examination, blood collection, administration of a questionnaire, and stereoscopic color fundus photography to determine age-related maculopathy. Standard univariate and multivariate analyses were performed.

RESULTS

After controlling for age, early age-related maculopathy was related to low total serum cholesterol levels in women and a high high-density lipoprotein (HDL) cholesterol level and a low total cholesterol/HDL-cholesterol ratio in men. After controlling for age and sex, age-related exudative macular degeneration was associated with higher hematocrit values (odds ratio, 1.09; 95% confidence interval, 1.00, 1.19) and higher leukocyte count (odds ratio, 1.10; 95% confidence interval, 1.00, 1.19). There was no statistically significant relationship between blood pressure, hypertension, or history of cardiovascular disease and exudative macular degeneration or geographic atrophy.

CONCLUSION

With the exception of relationships between serum lipids and early age-related maculopathy, and hematocrit values, leukocyte counts, and exudative macular degeneration, these data suggest that most cardiovascular disease risk factors are not related to age-related maculopathy. Further longitudinal study is needed.

Diabetes, hyperglycemia, and age-related maculopathy. The Beaver Dam Eye Study

PURPOSE

The purpose of this study is to examine the association among hyperglycemia, diabetes status, and age-related maculopathy in a population-based study of people between the ages of 43 and 86 years who lived in Beaver Dam, Wisconsin between 1988 and 1990.

METHODS

Age-related maculopathy was determined from stereoscopic fundus photographs.

RESULTS

In the nondiabetic group (n = 4291), no relationship was found between glycosylated hemoglobin and any signs of age-related maculopathy. Diabetes status was not associated with early age-related maculopathy. People 75 years of age or older with diabetes (n = 85) had a higher frequency of exudative macular degeneration (9.4%) than those without (4.7%) but had similar frequencies of pure geographic atrophy (3.8% for those with diabetes and 3.4% for those without diabetes). The relative risk of exudative macular degeneration in men with diabetes who were 75 years of age or older compared with those who did not have diabetes was 10.2 (95% confidence interval [CI]: 2.4, 43.7); for females it was 1.1 (95% CI: 0.4, 3.0).

CONCLUSION

These data suggest that diabetes is not related to early age-related maculopathy or geographic atrophy. The relationship of exudative macular degeneration to diabetes in older men, but not women, may be a result of chance. Further longitudinal study of this observation is needed.

An abbreviated assessment of ocular exposure to ultraviolet radiation

Individual behaviour has a very large effect on determining the exposure of the eye to solar radiation. To be able to examine the relationship between ocular exposure to ambient ultraviolet radiation and ocular disease, a model was developed previously that assessed cumulative ocular exposure from individual information on work and leisure activities. In this paper, we present a simplified version of the model that uses data on exposure during the middle of the day (9 a.m. to 3 p.m. solar time) during the northern 'summer' months (April to September). The ocular exposure determined by the simplified model is highly correlated with the full model (r = 0.98) and the simplified model predicts 62% of the total ocular exposure. This model should be useful for future epidemiologic studies of sun exposure and eye disease.

Carotenoids in the retina--a review of their possible role in preventing or limiting damage caused by light and oxygen

Two of the circa 600 naturally occurring carotenoids, zeaxanthin and lutein, the major carotenoids of maize and melon respectively, are the constituents of the macula lutea, the yellow spot in the macula, the central part of the retina in primates and humans. Of the circa ten carotenoids found in the blood these two are specifically concentrated in this area, which is responsible for sharp and detailed vision. This paper reviews the ideas that this concentration of dietary carotenoids in the macula is not accidental, but that their presence may prevent or limit damage due to their physicochemical properties and their capability to quench oxygen free radicals and singlet oxygen, which are generated in the retina as a consequence of the simultaneous presence of light and oxygen. Additionally, in vitro and in vivo animal experiments are reviewed as well as observational and epidemiological data in humans. These show that there is enough circumstantial evidence for a protective role of carotenoids in the retina to justify further research. Some emphasis will be put on age-related macular degeneration (AMD), a multifactorial degenerative retinal disease for which the exposure to light and thus photochemical damage has been suggested as one of the etiological factors. Recent attempts at nutritional intervention in this condition will also be reviewed.

Symmetry of disciform scars in bilateral age-related macular degeneration

The size of the final macular scar in subretinal neovascularisation (SRNV) is one of the most important determinants of final visual function in patients with subfoveal disease. We studied patients with bilateral macular scars from age-related subretinal neovascular membranes retrospectively in order to determine whether or not fellow eyes behave similarly. We found a significant correlation between eyes in terms of final scar size (r = 0.50, p less than 0.01). We found that 50% of fellow eyes with large macular scars (greater than 3 x 10(6) microns2) had similar sized lesions, while only 16% of fellow eyes with small macular scars (less than 0.5 x 10(6) microns2) had large scars (p less than 0.01). We discuss the significance of these findings in relation to the pathogenesis of subretinal neovascular membranes, and their implications for treatment.

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.

The biological effects of UV-B on the eye

The adverse effects of ultraviolet-B (UV-B) radiation on the eye have been suspected but only recently have they been quantified by epidemiologic studies in humans. These studies became possible as methods to qualify individual ocular UV-B exposure were developed. A consistent dose-dependent association between ocular UV-B exposure and two common types of cataract (cortical and posterior subcapsular) has been shown. Although suggested by experimental studies, at present, evidence does not exist to link UV-B exposure to senile macular degeneration. Ocular exposure to UV-B is also associated with several corneal changes, pterygium, climatic droplet keratopathy, and acute photokeratitis (snow blindness). Significant reduction in ocular UV-B exposure results from the use of eyeglasses and hats.

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.

Epidemiologic aspects of uveal melanoma

Although the underlying cause or causes of uveal melanoma have yet to be elucidated, important insights may be gained by examining the epidemiologic features of the disease. Uveal melanoma is an uncommon cancer with an incidence of only six cases per million population per year. It is most often diagnosed in the sixth decade and is somewhat more common in males. Apart from sporadic reports of family clusters, uveal melanoma is not considered an inherited disease. Whether some environmental exposure triggers the development of uveal melanoma remains an open question. Sunlight has been proposed as an environmental risk factor because sunlight is known to cause melanoma of the skin and both diseases are rare in nonwhite races. Unlike cutaneous melanoma, however, rates have not been increasing over time and do not vary by latitude. This paper evaluates the available evidence for sunlight and other potential risk factors for uveal melanoma, highlighting areas requiring further research.

Epidemiology of eye disease in the elderly

Most of the estimated 40 million blind individuals in the world are in the older age groups. Data on blindness and visual impairment are primarily from blindness registries and prevalence surveys in different countries throughout the world. The quality of these data vary tremendously from one country to another, and comparability of the results from different studies is difficult. However, all studies indicate an increase in the prevalence of visual loss and blindness with increasing age. Cataract is the most prevalent eye disease in the world and is a major cause of visual loss in developing as well as in developed countries. Other major eye diseases in the elderly include age related macular degeneration, glaucoma, and diabetic retinopathy. A number of risk factors have been suggested for cataract, age related macular degeneration, and glaucoma, yet few have been well established. Certain factors for these conditions are similar, including age, hypertension, prolonged exposure to sunlight, and nutritional factors such as Vitamin E. Epidemiologic studies are needed to define the risk factors for these different eye diseases with the goal of decreasing risk of disease and possible disease prevention, as well as developing better estimates of the magnitude of the problems of visual loss and eye diseases in the elderly.

Light and macular degeneration: a biophysical and clinical perspective

The evidence linking photic retinopathy to ageing macular degeneration (AMD) is compelling but circumstantial. The biophysical foundations of ageing theory are presented, in addition to an analysis of retinal senescence and the potential contributory role of photochemical retinal damage. Although there is pressure to implement clinical therapy for AMD based on laboratory studies of photic retinopathy, there is no evidence at this time that any such therapy is effective. Nonetheless, until the relationship between photic retinopathy and AMD is better understood, it is appropriate for individuals to use ultraviolet and deep blue protective sunglasses in bright environments, particularly if they have reduced ocular pigmentation or if they are aphakes or pseudophakes without an ultraviolet-protective intraocular lens.