“Beauty is in the eye of the beholder,” as the saying goes. Who would have thought this old proverb could be so true? Imagine you’re about to gaze upon a famous painting. Which eye would you use? Except for those of us who are ambidextrous, each of us is either right or left-handed. But this form of laterality doesn’t just apply to our hands and feet, it’s also true for the eyes. Why do we have a dominant eye?

Unless you practice archery or another precision sport, or if you’ve ever needed to look through a keyhole, it's unlikely you're aware of which eye is dominant. But if you have a tendency to favor your right hand or right foot in various activities, the same is true for your right or left eye... indeed one is dominant over the other. This is most noticeable if you look instinctively into a microscope, telescope or other viewing instrument.

In 2015, researchers from the neurofunctional imaging group of Bordeaux (GIN) observed using Magnetic Resonance Imaging (MRI) that the area of the visual cortex corresponding to the dominant eye was more extensive. Their study also contributed to gaining a better understanding of the role of brain symmetries in hemispheric specialization. This refers to the fact that: “certain cognitive functions are preferentially hosted by a brain hemisphere," explains Emmanuel Mellet, a researcher at GIN. “Classically, for example, we attribute language function to the left hemisphere, while spatial attention mobilization functions are attributed to the right hemisphere.”

We spontaneously use one eye over the other, with the right eye being dominant in two thirds of the population. Thus, distinguishing between righties and lefties solely based on handedness seems inadequate. More precisely, we are characterized by a combination of literalities (eye-hand-foot) that is either homogenous (all right or all left), or crossed (I can be right-handed and footed, but with a dominant left eye). This is why ocular dominance is of interest in studies of laterality. For example, the GIN team noticed that "lefties," particularly those with a dominant right eye, show greater lateralization on the right side. Because the circuits devoted to spatial attention and gaze are activated in the brain’s right hemisphere, it's easier to understand why a "lefty" tennis player or boxer might have an advantage (against a right-handed opponent).

Finally, keep in mind that the tests available for determining your dominant eye are generally devoted to distance vision (static), but near and dynamic vision deserve further study as well. For example, when reading this article, which eye led the way in moving your gaze across the page?