Yes, they are, along with all other foods rich in vitamin A, says Michael F. Marmor, a professor of ophthalmology at the Stanford University School of Medicine. The body uses vitamin A to support nerve cells in the retinas that help maintain normal vision. People who are deficient in A are susceptible to a host of vision problems, such as night blindness. Many red, yellow, orange, and leafy green vegetables — including sweet potatoes, kale, mangoes, and papayas — contain vitamin A, as do eggs and liver.