Vitamin D has been found to reduce the effects of aging on visual acuity in mice and to improve the vision of older mice significantly.
Of course, mice are not tiny furry humans, so these results may or may not mean anything for other species. However, I personally find that my 48 year old eyes began to work a lot better a couple of years ago when I began transitioning to a paleo diet and supplementing with vitamin D3. At the time, I’d been putting off seeing an ophthalmologist and getting glasses to correct the eyestrain and decreased visual acuity I was experiencing. In particular, I was finding that if I focused at a short distance for a few minutes, my eyes would take several minutes to adjust to longer distances. I almost failed a vision test when renewing my driver’s license because I made the mistake of reading on my iPhone while waiting for the test. My eyes didn’t have enough time to adapt to the further distance.
About a month after starting to take D3 (4,000 IU per day, except when I get a lot of sun), I was very surprised to notice that the slowness to adapt to distance changes was no longer happening. It seemed as if my corneas were now more flexible (corneas naturally get harder with age). While I still have a little trouble with reading small type, I continue not to need glasses and have no unusual eyestrain or blurring. I have not had my visual acuity or night vision tested, but I am convinced that they are better than they were.
That’s one of the many unexpected side benefits of taking an evolutionary perspective on personal health.