Cross-eye dominance is a condition wherein your brain prefers the visual input from the eye opposite your dominant hand. Roughly 90 percent of the population is right-handed, but approximately 30 percent of the population is cross-eye dominant.
Almost everyone – about 99 percent of the population – has a dominant eye, but there are some rare folks who never develop ocular dominance.
In other words, if ten people read this – I don’t know how possible that is, but one can always hope – one of those readers will be left-handed, but three will have cross-eye dominance.
What causes ocular dominance? It isn’t entirely clear. What IS known is that the brains of a number of animals that have binocular vision (including humans, those wretched meat bags) form ocular dominance columns, which are line-shaped structures on the primary visual cortex.
So far, it looks like they form in utero, meaning it’s likely genetic.
That means there isn’t a darn thing you can do about it; you can’t become left-handed if you’re right-handed. You can learn to use your left hand (Thomas Jefferson learned how to write in Latin in one hand, and in Greek with the other) but you can’t decide you’re left-handed and you can’t decide not to be cross-eye dominant.
This matters because cross-eye dominance impacts shooters. If you’re right-handed but left-eye dominant, you’ll have issues when you shoot, as getting a sight picture will be difficult since you practically have to put your head across your body to get a proper sight picture.
Cross-eye dominance was also a plot point in “Fire Birds,” an absolutely TERRIBLE movie about helicopter pilots starring Nicolas Cage. Anyone else remember that train wreck? Anyway . . .
How do you tell which of your eyes is dominant? There are a few different simple tests.
First is the Miles test. It’s old (pre-Roaring 20s) it’s easy, and it works. Normally you’re supposed to use a rolled up newspaper or something, but you don’t actually need to.
Find a relatively distant object, say a painting, picture, wall clock or knick-knack on the other side of the room. Focus on it with both eyes open.
Now take your hands, hold them up together and make a triangle, with an opening in the middle with the tips of your thumbs and index fingers touching. Move the triangle to the object, so that the object appears inside the triangle. If you want to, you can use a rolled-up newspaper or paper plate instead, but again you don’t have to.
Now make the triangle smaller by moving one hand over the other, until the object is basically all you can see inside the little window between your hands.
Now close one eye. Open it, then close the opposite eye. When the picture moves, you’ve found your non-dominant eye.
Some people have problems closing one eye. If that’s you, here’s what you do:
Instead of closing one eye and alternating them, keep the window between your hands small and slowly bring your hands back to one eye, keeping the focal object in the window between your hands. Then push it back out, and repeat while bringing your hands back to the other eye.
What you’ll notice is that while bringing the window back to one eye, the picture stays stable and centered. That’s your dominant eye. If you have to move your hands to keep the object in view, that’s your non-dominant eye.
Another common test is the Porta method. The initial setup is the same; find an object on the other side of the room and focus on it. Bring up a finger or your thumb so it’s between your eyes and the object or just under it, sort of like focusing on your front sight.
Close one eye, then open it and close the other eye. I’m pretty sure you get where this is going; when your thumb or finger moves, that’s your non-dominant eye. Alternately, you can bring your thumb or finger back to one eye, then extend it and bring it back to the other eye. The eye you can bring it straight back to is your dominant eye.
If neither of these tests work for you…you need to see an optometrist.
What to do about cross-eye dominance for shooting? That will have to wait for another time.
Any of you out there cross-eye dominant? Just want to rant? Sound off in the comments.