There are several different nutritional supplements that can be beneficial to your ocular health.
For those with macular degeneration, taking a vitamin that specifies the AREDS 2 formula are recommended. These can help slow the progression of the disease process, but there is no evidence that they help prevent macular degeneration if you do not already have it.
For dry eyes, many have claimed that taking Omega 3 fatty acids can be of some benefit. There are no confirmatory medical trials, there is significant anecdotal evidence that these decrease inflammation of the ocular surface and increase patient comfort.