Eat healthy. Although many foods (fruits, vegetables, fish and some plant oils) have been found to help keep the eyes (and body!) healthy, the average person should not lose vision by not eating enough of them. Those at risk for certain diseases such as macular degeneration may benefit from a higher amount of beta carotene, and vitamins e and c, but there is no proof that healthy eyes will benefit from them.
Pigmented. A healthy diet rich in fruits and vegetables is good for anyone but we've noticed that the ones which are highly pigmented like plums, peaches, etc. Are probably of most benefit. Also don't forget veggies like carrots, beets, green leafy veggies, etc. We're looking for the pigments which give the plants color and act as antioxidants. This is especially important for macular degneration.