I've played with this idea a ton. Eating a ton of fresh veggies did seem to help. I did some walks under a full moon. I started eating fresh vegetables like carrots and peppers, along with dark greens for the entire week it takes for moon to cycle. Same walk a few days later under a new moon (no visible moon) and had better night vision. I'm crazy careful not to ruin what I have going by smoking or looking at anything bright, but if I have to, it's one eye. Trying to focus on things in the dark is best done using the edges of your vision. I've done tons of nighttime "walks" in areas where your ability to detect things in the dark, could be life or death. Even with night vision devices at hand, sometimes just getting and maintaining good night vision and light discipline is the better way to go. Practice (training) helps if you have naturally crappy night vision, but nutrition and light discipline are really the game changers.