现有的资料表明，随着年龄增大出现的视网膜黄斑退行性变（macular degeneration）并不少见，在美国40岁上人群中本病的发生率大于6%。另外，在发达国家约有一半的失明因本病所致。由此可见，本病的危害非常大。最近有研究表明，易患视网膜黄斑病变的个体经常进食锌、抗氧化剂（如维生素C或E、胡萝卜素等）或Ω-3-脂肪酸（即不饱和脂肪酸）可显著降低其发病率。

已知两个基因变异（注：分别被称之为CFH和LOC387751S）可显著增加黄斑退行性变的发病率（其增幅分别为11倍和15倍）。因此，专家们建议存在上述基因变异的个体在日常生活中应多食富含锌、β胡萝卜素、叶黄素或玉米黄质（lutein/zeaxanthin），及Ω-3-脂肪酸的食品，如胡萝卜、蔬菜、水果和鱼油等。

Diet tied to lower risk of vision loss in old age

NEW YORK (Reuters Health) - For people at a higher risk of losing central vision as they age, eating sufficient levels of certain dietary nutrients could help protect their eyes. A new study finds that among people with a genetic susceptibility to macular degeneration -- vision loss caused by erosion of the retina - those who ate higher levels of zinc, antioxidants or omega-3 fatty acids cut their risk of developing the disease by as much as a third compared with those who ate lower levels of the nutrients.

"Therefore, clinicians should provide dietary advice to young susceptible individuals to postpone or prevent the vision-disabling consequences of (age-related macular degeneration)," the researchers wrote in the journal Archives of Ophthalmology. Age-related macular degeneration is common, accounting for half of all cases of blindness in developed countries, they note.

　　In the United States, the condition occurs in more than six out of every 100 adults over age 40. Though patients can be treated with medications and surgery, none of these cures the disease. At least two gene variations are known to raise a person's risk for developing the condition compared to the general population. One of the variations (called CFH) increases a person's odds of macular degeneration up to 11-fold and another (called LOC387715S) raises them by up to 15-fold.

To see whether these especially susceptible people might reduce their risk, the researchers, based in the Netherlands, surveyed the eating habits of more than 2,000 participants over the age of 55. All were tested for the macular degeneration susceptibility genes. All the participants also had eye exams every three years for the next decade to determine who suffered vision loss. Among people with the CFH variation, greater amounts of either zinc, beta carotene, omega-3 fatty acids or lutein/zeaxanthin in the diet was linked to a smaller risk of macular degeneration.

For instance, 39 out of every 100 people who ate the lowest amounts of omega-3 fats (about 22 milligrams per day) developed vision loss, whereas 28 out of every 100 people who ate the largest amounts of omega-3s (268 mg per day) had vision loss.   For those who had the LOC387715S variation, reduced risk of vision loss was seen among people who ate greater amounts of zinc or omega-3 fats. In their case, for example, 25 percent of people who ate 11.85 mg per day of zinc developed macular degeneration, compared to 33 percent of people who ate just 7.5 mg per day. "To achieve this benefit, it does not appear necessary to consume excessive amounts of these nutrients; the recommended dietary allowance will suffice," the authors note.

The recommended dietary allowance in the U.S. for zinc is 11 milligrams daily for men and 8 milligrams for women. Men are recommended to consume at least 1.6 grams of omega-3 fatty acids a day, and women 1.1 grams. Good sources for zinc include oysters, red meat, nuts and beans. Oily fish are some of the best food sources for omega-3 fats, while beta carotene is found in carrots, sweet potatoes and other vegetables and fruits. Lutein and zeaxanthin are abundant in eggs and green leafy vegetables. The authors did not work out whether or how these nutrients are responsible for the prevention of macular degeneration.

SOURCE: Archives of Ophthalmology, June 2011.