Improved Nutrition Could Help Prevent Vision Loss

“The traditional thinking is that as age increases, visual sensitivity decreases. But what we are saying is, maybe that’s not inevitable,” said D. Max Snodderly, Ph.D., head of the laboratory at The Schepens where the research was done. “Improved nutrition could help to retard the loss of visual sensitivity with age. Perhaps the gradual loss of vision in many older people is not an inevitable consequence of the aging process.”

In the latest study, Schepens scientists have found that macular pigment in the retina – an accumulation of yellow compounds from fruits and vegetables – may prevent age-related vision loss.

The macula, about the size of a pencil eraser, is at the center of the retina and is responsible for acute vision. Age-related macular degeneration, the leading cause of blindness in people over age 65 in western industrialized nations, occurs when the macula is destroyed by the aging process.

Snodderly, with co-authors Billy Hammond, a former postdoctoral associate now at Arizona State University, Phoenix, and Billy R. Wooten, Professor of Psychology at Brown University, report in the current issue of Investigative Ophthalmology & Visual Science (Feb. 1998, Vol. 39, No. 2) that macular pigment or dietary factors associated with it appear to protect the retina from loss of sensitivity, when the eye is adapted for light as well as for dark. The research was funded by the National Institutes of Health, the Massachusetts Lions Eye Research Fund, and Kemin Foods.

Macular pigment is composed of two chemicals, lutein and zeaxanthin, that are part of the family of compounds known as carotenoids. These compounds are contained in plants and protect them from light damage. Particularly high concentrations are contained in dark green and orange plants and fruits, like spinach, broccoli, green beans, corn and peaches. (But not carrots. Although carrots are good for Vitamin A deficiency, the retina does not take up beta carotene, which is the main carotenoid in carrots.) “If you eat a lot of fruits and vegetables, you will be getting a lot of carotenoids,” Snodderly said. “This already fits in with public health recommendations for a wide range of health issues – increase intake of vegetables and fruits.”

The scientists measured macular pigment and visual sensitivity of 27 healthy older subjects, ages 60 to 84, and compared them with 10 younger healthy subjects, ages 24 to 36. Visual sensitivity is how much energy is required to detect photons. Low sensitivity, usually associated with aging, means that it is more difficult to see light and thus, there is some vision loss.

The researchers measured macular pigment density (how much light the pigment absorbs) by flashing blue and green lights in an alternate pattern so the lights appeared to flicker. The blue is absorbed by macular pigment, but not green. The amount of blue light required to be equally as effective as the green yields the pigment density.

This technology, which could become an important tool in predicting the risk for macular degeneration, is the subject of a recently filed patent application.

As expected, visual sensitivity declined significantly with age. However, macular pigment was a clear determinant of visual sensitivity: Subjects over age 60 with high macular pigment density had the same visual sensitivity as the younger subjects. Older subjects with low macular pigment density had lower visual sensitivity than the younger subjects.

“The results show that high macular pigment density was associated with the retention of youthful visual sensitivity,” the authors write, “which suggested that macular pigment might retard age-related declines in visual function.”

Macular pigment density also appears to be correlated with factors that increase the risk of disease, such as age-related macular degeneration. For example, smoking, female gender and blue irises all are risk factors for the disease, and people with those risk factors also have lower macular pigment density.

Conversely, people with higher macular pigment density are associated with factors that decrease risk, such as high blood concentrations of carotenoids, high dietary intake of lutein and zeaxanthin and dark irises.

“Taken together, the evidence suggests that macular pigment may protect against retinal disease by reducing damage that occurs as we age,” Snodderly said.

Further, macular pigment density may be useful as a predictor for overall ocular health, the researchers said, because macular pigment density correlates with preservation of clarity of the lens as well as sensitivity of the retina. Since previous research by others showed that reduced visual sensitivity may predict development of advanced age-related macular degeneration, then, the researchers suggest, increasing macular pigment density might prevent people who are mildly impaired from advancing to the worst stages of the disease.

They write: “It is possible that, by improving protection, retinal or retinal pigment epithelial cells that may be damaged, but still viable, could recover.”

Said Snodderly, “It appears that people lose visual sensitivity before the worst stages of disease. But with the right nutritional program, you might prevent the low macular pigment group from getting worse, and in the best cases even recover some of the lost function.”

The research also has resulted in a way to tailor dietary recommendations to an individual, the scientists said.

“Our studies have suggested that individuals differ in their ability to absorb nutrients from food into their tissues,” Hammond said. “Thus, some individuals can have relatively high intake of fruits and vegetables and high nutrient blood levels but actually low levels of retinal nutrients. The ability to easily measure macular pigment in vivo may allow us to idenitify such individuals and determine whether they are at special risk for disease. In the future we may be able to use such technology to tailor our dietary recommendations based on individual responses rather than relying on averaged effects.”