The second common eye disorder, cataract, affects more than half of all Americans age 65 and over. A cataract is a cloudy spot in the lens of the eye. In the healthy eye, the lens, composed of water and protein, is transparent. For reasons that are not fully understood, this protein can clump together, forming a cloudy spot that causes light to be distorted as it passes through the lens.
Most cataracts are related to aging, and more than half of all Americans age 65 and over have a cataract. In addition to age, diabetes can also cause proteins in the lens to clump. People with diabetes, therefore, are more likely than the general public to form cataracts and often develop cataracts at a younger age. Symptoms of cataracts include blurry vision, reduced night vision, fading of colors, and problems with glare.
Besides diabetes and advancing age, smoking and long-term exposure to the sun’s ultraviolet rays are believed to increase the risk for developing a cataract. Medicines such as steroids can also cause cataracts.
Attention has also been focused on the biological process of oxidation as one of the factors that may lead to both AMD and cataract. This in turn has raised interest in the potential of antioxidants, compounds that appear to mitigate some of the damage caused by oxidation.
Another area of research has concentrated on diet, specifically diets high in green leafy vegetables.
Some of the best news regarding eating for eye health involves consuming leafy green vegetables like spinach, kale, collards, and broccoli. For a number of years, evidence has been accumulating that people whose diets are relatively high in leafy green vegetables are less likely to develop AMD.
Scientists believe two substances, lutein (LOO-tee-in) and zeaxanthin (zee-ah-ZAN-thin), may be responsible for this effect. Both lutein and zeaxanthin are carotenoids (plant pigments), similar to the better-known beta-carotene.
Lutein and zeaxanthin are of particular interest because the macula contains higher concentrations of these two substances than does any other spot in the body. In fact, the macula is yellow due to its rich stores of lutein and zeaxanthin, which are yellow pigments. (This yellow color is masked by the green color of chlorophyll in many plant foods.)
Researchers have found that people with advanced AMD tend to have lower blood concentrations of lutein and zeaxanthin than people without the disease. Studies comparing the diets of those with AMD to those free of the disease have also indicated that people with low dietary intakes of foods containing lutein and zeaxanthin are more prone to the disease. In one study, researchers found that people who typically ate lutein- and zeaxanthin-rich greens two to four times a week were half as likely to have AMD as people who ate those foods less than once a month.
Authors of a review that examined the results of years of research on this subject also concluded that “generous” consumption of lutein and zeaxanthin from foods such as broccoli and spinach was associated with up to a 40% reduction in risk for AMD. The same level of intake of these carotenoids was also linked to a 20% reduction in the risk of cataract.
Lutein and zeaxanthin may confer their protection by absorbing the potentially damaging blue light found in sunlight before it causes harm to the retina. The two compounds may also act as antioxidants, neutralizing damage to cells caused by “free radicals,” a type of damaging oxygen.
There is not yet enough information to make a specific recommendation for including leafy dark greens in the diet for the sole purpose of benefiting the eyes. However, leafy dark greens are among the most nutritionally dense foods nature provides. They are low in calories and contain a wealth of nutrients such as vitamin A in the form of beta-carotene, vitamin C, vitamin K, fiber, folate, iron, and magnesium. Because some of these greens can be unfamiliar, a cooking guide for greens is here.
Leafy greens are not the only source of lutein and zeaxanthin. Other vegetables and some fruits contain either one or both of the compounds. In a study analyzing the lutein and zeaxanthin content of a number of fruits and vegetables, researchers found that corn, kiwifruit, red grapes, spinach, zucchini, yellow squash, orange peppers, and orange juice were among the foods that contained substantial amounts of one or both of the compounds.
Egg yolks, too, are an excellent source of both lutein and zeaxanthin, because of the plant-based diet of the chickens producing the eggs. For people with diabetes, however, and others at high risk for heart disease, dietary guidelines from the National Cholesterol Education Program suggest limiting total daily cholesterol intake to 200 milligrams (mg) or less. Given that a large egg yolk contains 212–220 mg of cholesterol, fruits and vegetables are generally more healthful sources of lutein and zeaxanthin.