AMD is also a cousin of coronary heart disease, and shares with it several common ancestors, such as atherosclerosis (Am J Epidemiol, 1995; 142: 404-9), hypertension (Arch Ophthalmol, 2000, 118: 351-8) and high cholesterol. AMD also afflicts nearly 40 per cent of those with diabetes (J Longev, 1998; 4: 24-6).
Many other risk factors for heart problems are also risk factors for AMD. These include smoking (especially in women), age (3.8 per cent of Americans have either intermediate or advanced AMD by the time they reach age 50-59 and, by the time they are 70-79, this proportion will have increased to 14.4 per cent) and gender (women appear to be at a slightly greater risk than men).
Increasingly, the evidence points to a role for industrialized food-processing in the onset of heart disease and diabetes. More and more studies of heart patients are finding that they have elevated levels of homocysteine, an amino acid derived from the normal breakdown of proteins in the body. Raised levels of this amino acid are an indication that something has gone awry (see Viewpoint, p 5).
Crucial to this process is the presence of adequate levels of certain B vitamins. Other studies of heart patients have shown that they are deficient in these vitamins, and that adequate B-vitamin supplementation can reduce the incidence of heart attack and angina (Res Commun Mol Path Pharm, 1995; 89: 208-20). Links have also been made between the onset of diabetes and heart disease and deficiencies of chromium.
Natural sugars and grains contain adequate concentrations of chromium to support the metabolism of high-carbohydrate foods. However, virtually all B vitamins and chromium are removed during the refining process of most of the sugars and processed foods that now make up the bulk of the typical Western diet. Diets high in processed carbohydrates are nearly always deficient in chromium.
Another area that medicine has never explored is its own hand in the development of the AMD epidemic. Many of the drugs routinely prescribed for older people may well accelerate eye damage.
Doctors push aspirin because it thins the blood, thereby reducing the risk of blood clots. But, apart from poor effectiveness and the risk of gastrointestinal bleeding, new research suggests that long-term aspirin use can accelerate macular degeneration and contribute to retinal hemorrhage.
More than a decade ago, Dr J.D. Kingham wrote a letter to the prestigious New England Journal of Medicine (1988; 318: 1126-7) in which he noted that, in his clinic, many of the elderly patients who came to him with decreased central vision and macular hemorrhages had a history of recent ingestion of aspirin and other drugs known to affect platelet function or the bloodclotting process.
NSAIDs (non-steroidal anti-inflammatory drugs) have been shown to increase the risk of cataracts - a risk factor for the later development of AMD - by as much as 44 per cent (Ophthalmology, 1998; 105: 1751-8).
Many other common drugs, however, also contribute to a slow and steady degeneration in the eye, and hasten the onset of macular degeneration by making the eye more light-sensitive. These include certain antibiotics, psychotherapeutic medications and NSAIDs (Int J Toxicol, 2002; 21: 473-90). Phenothiazine antipsychotics, antidopaminergics (for motion sickness) and calcium antagonists have also been associated with AMD (Arch Ophthalmol, 2001; 119: 354-9).
However, some of these adverse effects of drugs are temporary. People taking sildenafil (Viagra), for example, often experience transient visual changes, described as ‘blue tint’, which usually lasts for four hours after taking the drug, according to the Viagra package insert.