Our eyes are a lot like our hands, because we typically have one that is dominant over the other. If you’ve ever aimed down a set of sights or used a traditional camera, then you’ve probably noticed that one eye works better than its counterpart. This is because one eye is more in tune with the brain, sending stronger and more accurate signals.
Eye dominance can vary from person to person, with some people having a great difference between their eyes and others having less. In fact, ocular dominance is something closely considered by many eye doctors for certain prescriptions eyeglasses or preparing for laser corrective surgery. But what causes one eye to be dominant over the other in the first place, and how can you tell which eye it is?
Why is one eye dominant?
Eye dominance is hardwired into our brains, much like hand dominance. The section of the brain devoted to processing visual information is called the visual cortex, and it is within this cortex that stripes of nerve cells, called neurons, read information from the eyes. The full workings of the relationship between the brain and the eyes are very complex, but when it comes to eye dominance, it’s all in the neurons.
These neurons are called dominant eye columns. They seem to respond with a level of preference for one eye or the other. It is this combination of neurons playing favorites that helps contribute to the development of binocular vision in humans.
But there is a lot of flexibility in this area. Research has shown that these dominant eye columns are not always set in their ways, and that a level of plasticity exists. This explains why it is difficult but not impossible to force a change in eye dominance.
Strabismus and amblyopia
Typically the “dominant eye” we talk about refers to one eye communicating a little more strongly with the brain while both eyes are still functioning normally. In rarer cases, the term can have a more literal definition. With dysfunctional cases of strabismus (crossed or walled eyes) or amblyopia (lazy eye), the dominant eye describes the “normal” eye, if there is one. An apt comparison here would be a naturally left-handed individual versus someone who is forced to use their left hand after an injury to their right.
Special eyeglasses or other vision tools may be prescribed to fix this rarer form of eye dominance by improving vision and performance in the non-dominant eye.
Types of eye dominance
Eye dominance is not always as straightforward as one eye outperforming the other. In other words, a person can have different types of dominance in each eye. There are three main types of eye dominance and they don’t always apply to the same eye, this is called mixed ocular dominance.
The sighting dominant eye is the preferred eye for fixing your sights on something. This eye is dominant for shooting guns, using traditional cameras or even viewing items under a microscope.
The motor dominant eye stands the best chance of maintaining fixation on the near point of convergence.
The sensory dominant eye is the eye with better vision. This applies doubly because one eye may have dominant close vision while the other may be better for distance viewing.
How to test for eye dominance
Eye dominance usually has no medical relevance, and most people can go years or even their whole lives without it ever mattering. However, if you play certain sports or are considering monocular vision correction, it may matter which eye is dominant.
The most accurate way to test for eye dominance is in a specialized vision clinic with equipment for something called a non-sighting test. This involves measuring responses to stimuli exposed to each eye separately and requires a professional.
However, for a general idea of which eye might be dominant, there are plenty of simple (and free!) ways to check for ocular dominance. These are called sighting tests and while there are many different versions of these tests, they all involve the same basic steps:
- Extend your arm and point your thumb upward.
- Line your thumb up as perfectly as you can with an object in the distance.
- Alternate closing one eye at a time
- When you close one eye and your thumb appears to “jump” away from the distant object, that means the eye you closed was your dominant one.
If you wear prescription eyeglasses, you do not need to remove them to perform this sighting test.
Can eye dominance change?
We mentioned that eye dominance can be altered with therapy and specific medical devices such as eyepatches. This is rarely necessary and is usually undergone by avid gun or archery enthusiasts who want their dominant eye to match up with their dominant arm to make shooting easier.
Aside from that, it is thought that eye dominance may sometimes change on its own, and those changes may be as natural as any other of our eyes’ aging processes. This can mean a complete swap from one eye being dominant to the other, or it can be as simple as the dominant eye increasing or decreasing in its dominance.
Overall, you shouldn’t worry about ocular dominance, so long as your eyes are healthy. Keep up with regular eye exams and wear 100 percent UV-resistant sunglasses while you’re outdoors and your eyes, dominant or not, will stay healthy for years to come.