Their findings support previous evidence suggesting that the natural compounds could help prevent cataracts, which affect nearly 20 million people in the United States alone and require expensive, surgical treatment.
The researchers from Ohio State University say theirs is the first laboratory evidence that these carotenoids help protect the eyes.
"Along with the many environmental, lifestyle and genetic risk factors associated with cataracts, exposure to ultraviolet radiation from sunlight and oxidative stress appear to be the most relevant in this disease," said study co-author Joshua Bomser.
"Our results are the first to provide physical evidence suggesting that lutein and zeaxanthin decrease damage caused by ultraviolet radiation."
The Ohio researchers treated human eye lens cells with varying concentrations of lutein, zeaxanthin or vitamin E. They then exposed these cells, along with a batch of untreated cells, to doses of ultraviolet-beta radiation for 10 seconds. UVB radiation is thought to be the primary environmental culprit in causing skin cancer as well as initiating cataract disease.
"The dose of UVB radiation we used on the cells is about the same amount a person receives when they get a mild tan," Bomser said.
Adding lutein and zeaxanthin to the cell cultures provided double the protection from UVB damage - the antioxidants reduced signs of damage by 50 to 60 per cent, while vitamin E only reduced the same signs of damage by 25 to 32 per cent, according to the study in this month's issue of the Journal of Nutrition.
The researchers also found that it took far less lutein and zeaxanthin as vitamin E - about 10 times less - to get this protective effect.
"The lens is equipped with antioxidant defense mechanisms designed to guard against the harmful effects of ultraviolet radiation and oxidative stress," Bomser said.
"In addition to protective enzymes and compounds like vitamins C and E, we think that low concentrations of lutein and zeaxanthin in the eye lens help shield the eye from the harmful effects of UVB radiation."
Bomser noted that the scientists do not yet know how these two antioxidants get into the eye.
"Lutein and zeaxanthin accumulate in the retina and in the lens of the eye, but we're not sure how they reach the eye in the first place. They travel through the bloodstream, but the lens doesn't have a blood supply," he explained.