Your eyes control more of your neck than you think. Try turning your head left and right, then repeat while keeping your eyes fixed the opposite direction. You'll feel the difference in how tight your neck gets.
If your neck feels tight or stiff when you try to turn it, don't stretch it. Try this first. What I'm going to have you do is just test where your neck can move. So turn it to the right and turn it to the left. And we're not trying to force it into a big range of motion. We're just trying to get an idea of how far does it really go on its own. Now, from there, what I want you to do is if we're going to test to the right, get an idea of how far you can go. Come back to the middle. We're going to turn our eyes all the way to the left. So you're looking over to the left and you're going to hold them there. Now turn your head to the right, again, keeping your eyes over here, and see what you feel. Try the same thing the other way. Turn your head to the left, come back, keep your eyes to the right, and now turn your head left and see what happens. Now there's no right or wrong answer here, but the idea is it shows that your eyes can impact how your neck moves, which means if there's stiffness or pain in your neck, that your eyes can definitely have something to do with that.
Stop Stretching Your Neck. Try This Instead (It Might Improve Your Vision Too)
