A human being's eyesight is a cherished possession. The structure and function of the human eye are related to a person's vision. When we view something, the image of it lingers in our minds for a brief while. However, after seeing that object several times, we will begin to recognize it. The image of the object was 'imprinted' in our minds, as we say. This depicts the relationship between our eyes and minds during the seeing process. But why are we born with two eyes? Almost all of the species that live around us have two eyes, not just humans.
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Key terms: binocular vision, fusion vision, two-eyes, cornea, brain, depth perception.
The Structure of the human eye
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We know that the structure of the human eye is more or less similar to that of a camera. The image we see is the light that falls on the object and the restructuring of that light form image.
When we classify the parts of our eyes, we often catalogue three categories: external fibrous coat, middle vascular coat, and internal nervous coat. But rather than going into such a wide explanation, we can just discuss four parts of eyes that have relevance in this context: Aqueous humour, cornea, lens, and optic nerves. Aqueous humour is the topmost layer of the eyes that protect our eyes with fluid. Whenever our eyes are disturbed by a dust particle or any foreign substance, water overflow out of our eye due to the presence of this aqueous humour. The cornea is the visible part just behind the aqueous humour which permits the entrance of the light into the lens of our retina and optic nerves act as the connecting part between the eyes and our brain.
The video below explains this:
Human Eye One Shot Detailed Video Explanation:
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The Binocular vision
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Human vision is divided into two eyes. This does not imply that we can see objects with either of our eyes. At the same time, we can see almost clearly with just one eye. The same question then arises: why do we have two eyes? Binocular vision, sometimes known as two-eye vision, has a specific purpose. Let's look at how we can see images with binocular vision.
The path of our vision begins with the retina of our eyes. Through reflection, the rays from the left side of an object fall on the right- eye, and the light from the right side of the same object falls on the left eye. Through the aqueous covering of our eyes, the light falls on our retina. The lens of each eye refracts the rays to the optic nerves of our eyes and from there, the impulses of the light are taken to the brain through cross-structured nerves. By this process, a noticeable phenomenon is that the left-side brain gets the right-side image of an object. The optical visualization parts of our brain (occipital lobe and visual cortex) combine the image to give us an accurate and clear view of the image. Moreover, this gives us a three-dimensional view of the image before us.
Brain and the fusion vision
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Science clearly states that we not only see images with the help of our eyes, but also with the help of our brain. The brain receives the information from both the eyes, mix it into a single image for our recognition. So, we memorize and understand an image with the help of information provided by both eyes. Both our eyes act as an encrypted transmitter of partial information where the mind decodes their message. This phenomenon is called the fusion vision. The image was partially seen by both of our eyes but the final image or the vision was provided by our brain, creating a fusion of those images.
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The purpose of two eyes
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The purpose of a two-eye view in human beings (binocular vision) is simple: to provide clear and accurate vision. But the procedure of how the image form clearly through binocular vision is something complicated.
A clear view of objects that appears before us is provided due to the presence of two eyes. This makes us see even fainted images. A three-dimensional view is also made possible through binocular vision as both eyes see the same object from different angles. The location of objects is made more accurate with the help of the same binocular vision.
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Things to remember
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- Humans have a two-eyed vision, often referred to as binocular vision.
- Binocular vision helps the human brain to understand an image clearly and locate its distance.
- Aqueous humour, cornea, lens, and optic nerves are the parts in both the eyes that facilitate the clear vision human beings.
- The brain creates the image of the object which eyes see by creating a fusion of the images captured by both the eyes.
- Two eyes make it possible for human beings to perceive and interpret the vision through two eyes is known as depth perception.
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Sample questions
Ques: What is the need for a binocular vision for humans?
Ans: Binocular vision refers to the view of humans with the help of both eyes. We know that the complete vision of a human being is constituted by both his eyes. Following are the benefits of binocular vision:
- A clear view of objects.
- A three-dimensional view is made possible.
- It makes the location of objects more accurate.
Ques: How a human being gets 1100 vision with his eyes?
Ans: The position of eyes in a human face has a huge influence on the wide range of view. The field of vision expands with the ability of the iris to move to the corners of the eyes. Moreover, the human eyes are created in such a way to suit binocular vision. This facility has made possible a wide vision for human eyes which range from 950-1100 vision at the far peripheral of the field of vision.
Ques: Explain what do you mean by stereopsis of eyes?
Ans: Human eyes are constituted with binocular vision and with the help of the fusion vision of the brain, the distance of the objects that appear before we are given a clear idea. For a better view of the objects appearing before us, our eyes are faced at the front of our face, unlike some animals. This obviously will reduce the field of our vision, but the focus on a certain object becomes more accurate and thus we can make an appropriate assumption on distance as the brain comprises the image of different angles to make a concluding vision. This ability is referred to as the stereopsis of our eyes.
Ques: What happens if a human being doesn’t have a two-eye vision?
Ans: Some people in the world don’t have a vision in both of their eyes. This leads to an incomplete vision and they won’t have accuracy in locating an object. This means that they would feel things far away as close to them and even some people may feel the close things as far away from them. Some people lose their eyes due to accidents whereas some people are born with lazy eyes known as Amblyopia. This is a genetic condition that reduces or completely eradicates the vision of one eye.
Ques: Explain the science of depth perception with an example.
Ans: Depth perception is a concept that tells us the effect of binocular vision on a human being. It refers to the ability of human beings to interpret the images that we see through both our eyes, to get a final image.
Get a hollow tube and keep it close to your right eye. Make sure that it won’t hurt your eye (it is advisable to wear a spectacle) now, keep your left palm before your left eye. Now, when you have a look at both, you would feel that there is a hole in your left palm. This is due to the depth perception, because of which the brain combines both the images to constitute a final image.
Ques: Explain the structure of human eyes concerning binocular vision.
Ans: Aqueous humour, cornea, lens, and optic nerves are the important components of the binocular vision of human beings. Aqueous humour is the topmost layer of the eyes that protect our eyes with fluid. Water overflows out of our eyes due to the presence of this aqueous humour. The cornea is the visible part just behind the aqueous humour which permits the entrance of the light into the lens of our retina and optic nerves act as the connecting part between the eyes and our brain.
Ques: Humans had enjoyed the benefits of binocular vision during their primitive days. Explain.
Ans: The primitive human found his food through hunting and fishing. While hunting animals, humans kept a distance from animals and threw their weapons to kill them. For this purpose, a sharp location of animals was an inevitable feature. The binocular vision of humans has made them sharp and accurate in their hunting.
Ques: State a practical to show why two eyes vision is beneficial to human beings.
Ans: Close your right eye and look at an object before you, say a pen on the table. Raise your right hand and keep it a little bit far away from the pen. Now, try to point the pen from that distance. Without changing the position of your hand pointing at the pen, close your right eye and open the left eye. Now you would be wondering to know that your right hand is not pointing at the pen, now.
Thus, it is clearly stated that binocular vision is essential for us to be accurate in locating objects.
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