Last week I posted a late-night rant on ocular dominance, and since then I’ve read some Wikipedia pages that were kind of interesting.  It seems I was right that there is almost no correlation between dominant hand and dominant foot; however, there is a weak correlation between dominant eye and dominant hand.  I also determined that I am right-eyed.  This makes me like about 60% of the population, in that I’m right-handed, right-eyed, and right-footed.

The ocular dominance test I took before was some variant of the “Dolman” method, which doesn’t work for me because I am too conscious of what is being tested.  But the following test worked for me:  Look at something far away with both eyes open, and then point at it with your index finger extended at full length.  Obviously, you’ll see two index fingers, but you’ll naturally use one of them for pointing.  Once you’ve done this, if you close your eyes one at a time, the one that sees the finger lined up with the object you are pointing at is the dominant eye.  For another variation, if you find that you are pointing at the object with the index finger on the left, you are right-eye dominant, and vice-versa.  When I first did this, I thought that I was favoring my right eye just because I was pointing with my right hand, meaning that lining up my right eye won’t leave the other image of my hand blocking my view.  But when I tried the same test using my left hand, it was still more natural to line up with my right eye.

There were several interesting theories as to why left-handedness would develop in right-handed populations.  Most of them focus on the advantage the left-handed person would have in combat, since the right-handed opponent would be less practiced against left-handed combatants (and for that same reason left-handedness is more common in boxers and baseball players than in the general population).  But there isn’t a good theory as to why we aren’t all ambidextrous, or why there aren’t any isolated left-handed populations.

So back to my original hypothesis: when you go quickly from dark to light, you instinctively close the dominant eye and squint the weak eye.  Yesterday Stephanie and I were leaving a restaurant with some friends in the middle of a sunny day, and as we walked outside I noticed everyone except Stephanie was closing their right eye, but Stephanie was closing her left eye.  I later had her do the test to determine dominant eye (without saying why exactly) and it was indeed her left eye, which is consistent with my theory.

Now for more hypothesizing, Stephanie and I both have weaker vision in our dominant eye.  Is that a coincidence, or is it because the dominant eye is stressed more?