Age-related macular degeneration (AMD) is a leading cause of loss of vision in older persons in developed countries. Two new studies explore some of the risks, including dietary factors.

Introduction

Age-related macular degeneration (AMD) is a leading cause of loss of vision in older persons in developed countries. To-date, it has been thought that the disease starts as the non-neovascular form, and progresses to neovascular (NV) AMD. Risk factors suggested for AMD include hypertension, cardiovascular disease, increased body mass index, plasma fibrinogen levels, nutritional and antioxidant status, cigarette smoking, as well as genetic factors such as light/medium eye color, hyperopia, lens opacities, and dermal elastotic degeneration. Unfortunately, the studies done to establish these did not discriminate well between non-NV and NV forms of AMD. To redress this, the Age-Related Macular Degeneration Risk Factor Study Group conducted the study summarized here.

Method

This was a case-control study of subjects from 11 ophthalmic practices the New York area. They underwent a standardized interview, blood pressure measurement, blood sampling, visual acuity, iris color, and fundus photography. The interview and questionnaire covered dietary history, medical history (with an emphasis on cardiovascular conditions), medication use, smoking and alcohol use. The fasting blood samples were examined for a full lipid profile, vitamins A, E, and C, beta-carotene, selenium, and glutathione peroxidase.

Classification into non-NV AMD (227 subjects), NV AMD (182 subjects) and non-AMD (235 subjects) was done by masked examination of fundus photographs by independent graders. The non-AMD subjects, who had attended for a routine eye exam or other ocular diagnosis, had no medium or large drusen, and <7 small drusen in both eyes. The AMD subjects had a minimum of 30 small drusen in at least one eye, with NV demonstrated by subretinal blood, lipid or fluid, or serous pigment epithelial detachment.

Results

The mean age of the NV group was greatest - 70.8 years, vs. 69.4 years for non-NV AMD and 68.5 years for the non-AMD controls. About 60% of the entire study population was female. In general, NV subjects had less years of formal education, and were more likely to be blue-collar workers, than non-NV AMD and control subjects.

While systolic and diastolic blood pressure measurements were similar in the three groups, several hypertension-related variables were statistically associated with NV AMD, and these associations remained after regression analyses were made that took all the closely related variables into account. The associated factors were: diastolic pressure >95 mmHg, self-reported use of antihypertensive medication, and physician-reported hypertension or prescription of antihypertensives. Odds ratios ranged from 1.8 for a physician-reported hypertension history to 2.8 for use of more-potent-than-diuretic antihypertensive medication.

The existence of NV MD was associated with a higher cholesterol intake, after adjustment forage, sex, and total calorie intake. The statistical significance of an association was maintained between NV MD and raised high-density lipoprotein (HDL)-cholesterol after correction for other variables, but not between NV AMD and total cholesterol, triglycerides, or low-density lipoprotein.

Comment

This study found associations between NV AMD and moderate to severe hypertension, similar to those already reported by other investigators (e.g. the Framingham Eye Study¹). The absence of such associations for non-NV AMD in this study suggests to the authors that there may be differences in the pathogenesis of the two types of AMD. They go further to postulate that NV AMD and hypertensive disease have a similar underlying systemic process.

Support for this latter hypothesis comes from a new Australian study, which has assessed the association between dietary intake of fat or fish and the prevalence of AMD² The subjects were 3,654 people over 49 who were enrolled in the Blue Mountains Eye Study. Those with AMD were identified from masked grading of retinal photographs, with classification into early and late AMD using the Wisconsin system; the late AMD subjects were of two types - neovascular (NV) degeneration and atrophic degeneration. A food frequency questionnaire, completed by 89% of participants, allowed calculation of intake of dietary fat and fish.

After adjusting for age, sex, smoking, and a family history of AMD, more frequent consumption of fish appeared to protect against late AMD. Compared with a low consumption (less than once per month), adjusted odds ratios ranged between 0.23 and 0.52 for late AMD. There was little evidence of a protective effect of fish eating on early AMD. Subjects with a high total cholesterol intake, adjusted for total energy intake, were significantly more likely to have late AMD, whereas high intake of polyunsaturated fat was associated with a lessened likelihood of late AMD, roughly equivalent to that for eating fish more than 4 times a month. Fish intake can be regarded as a reasonable marker for dietary omega-3 fatty acid intake.

It is clear that subjects inherently at risk of developing AMD (family history, light eye color) can do something about it - stop smoking, cut alcohol intake, reduce all cardiovascular risk factors, and increase their omega-3 fatty acid intake, i.e. eat more fish!

Source

• Hypertension, cardiovascular disease, and age-related macular degeneration. L. Hyman, AP. Schachat, Q. He,  et al., Arch Ophthalmol, 2000, vol. 118, pp. 351--358

Footnotes
1. Systemic hypertension and age-related maculopathy in the Framingham Study. RD. Sperduto, R. Hiller, Arch Ophthalmol, 1986, vol. 104, pp. 216--219
2. Dietary fat and fish intake and age-related maculopathy. W. Smith, P. Mitchell, SR. Leeder, Arch Ophthalmol, 2000, vol. 118, pp. 401--404

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