Why do we Have Two Eyes?

The Necessity of Two Eyes

It is quite baffling that we have two eyes and require the use of two eyes simultaneously, even though we still have a sense of vision if we cover one of our eyes. The reason why we have two eyes is to enable two things in our brain, namely depth perception and an increased field of view. Typically, a pair of functioning human eyes are known to have a field of view of about 170 degrees, and humans are very capable of accurately determining the relative distance between the objects kept in front of them.


The Science of Depth Perception

Even though we have two eyes, we only see one image at a time. Our brain only sees images sent through one eye instead of perceiving and making sense of the information posted by both the eyes at the same time. So, what happens in our brains is that it alternates between the data sent from two eyes to allow us to see the third depth dimension. The ability to see the distance between the two objects in the field of vision is known as depth perception.


Since both the eyes are very close to each other, both of the eyes see almost the same picture. It is the job of our brains to make sense of the two images sent into our minds.


So, the process of sight begins when first, the light from the object strikes the lens of our eyes. This forms an inverted image of the object on our retinas. In the next step, the picture which is created with the help of the optic nerve, is sent to the brain for processing.


We, humans, have a significant advantage due to our binocular vision. Our binocular vision allows us to determine the exact position of any object placed in front of us. 


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Understanding our Eyesight Through Some Activities

There are certain activities that you can conduct to check why we require two eyes instead of one eye.


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To verify that we see only from one eye at a time, let’s try out this activity. Close one of your eyes and notice the brightness level of the images you see. Now, keep switching between the eyes. Do you feel a noticeable change in the brightness or the field of vision of the image you see? If your eyes are working correctly, you shouldn’t be able to ascertain any differences in the pictures you see from the two different eyes. This justifies the claim that we humans only see from one eye at a time, and the speed at which the brain switches between the two eyes is very fast for us to notice.

To understand the depth perception, there is a straightforward activity you can set up. You will need various objects, each with different shapes and sizes. Now, ask the volunteer to close their eyes while setting these objects in front of them.


Your setup should look somewhat like in the picture shown above. Once you are done with the setup, ask the volunteer to open one of the eyes. Give them a moment to get accustomed to their surroundings. Now, you have to point to any object and ask them to touch it. You will notice that your volunteer might almost always reach the objective that you ask them to, but they will struggle to touch it.


Now repeat the same experiment with both eyes open. The struggle would not be present anymore. Why was the volunteer struggling to reach the objects with one eye? Our brains rely on both of our eyes to determine the exact position of any object it sees. Since one of the eyes was closed, the brain only received half of the information. With half of the data, the determination of the position of any object is complicated, and the depth perception of our brain would be flawed. This is one of the main reasons why humans have two eyes and why we need the image from two eyes to function properly.

FAQ (Frequently Asked Questions)

Q1. What are some of the Benefits of Why do we have two Eyes Instead of one?

Other than having an improved field of vision and the ability to perceive depth, there are some other advantages of why we have two eyes instead of one. Two eyes help us gain a stereoscopic vision, i.e., the ability to register and make sense of three-dimensional space from any visual inputs. It also helps us to gain a wider angle, as with one eye, we would be able to see 150° while with both eyes, you get a 180° field of vision. Also, human beings are symmetrical, and so, we also require two eyes to maintain the symmetry of our face as well as our other body parts.

Q2. What is Amblyopia?

Amblyopia, or lazy eye, is the condition in which one or both of the eyes develop abnormalities in childhood. Amblyopia usually happens when the portion of our brain, which is responsible for the processing of the vision, fails to develop normally. The result, despite having two eyes, the things that we see appear to be blurred. It usually happens to infants post-birth or the children below the age of 8. The infants who are born prematurely or born underweight are more prone to develop this condition. This condition occurs when the brain cannot use both of the eyes together and thus loses the ability to perceive depth.