What can I eat to improve my vision?

Well rounded diet. Deficiencies are unlikely with a healthy and varied diet. Eat lots of foods with beta carotene (yellow/orange), omega-3 acids for dry eye and vitamin e.
Not much. The evidence out there is that vision cannot be improved by diet. Those with very poor dietary intake can certainly suffer from vision loss related to malnutrition. And most vision problems are related to focus issues (nearsightedness, farsightedness, astigmatism and/or cataracts) which have not been found to respond to any degree to dietary changes. Eat a well-rounded diet, and stay healthy!