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How Does the Human Eye See?
The human eye is a complex organ that uses different parts of the eye to transform light into images. The parts of the eye that are responsible for vision are the cornea, the iris, the pupil, the lens, the retina and the optic nerve. There are many aspects to how the eye works, with each part of the anatomy crucial in receiving light from objects and transferring them to the brain. How well the human eye can see is dependent on certain factors such as the health of the eye, the visual acuity as well as how much light is present and how obstructed their sight is.
In summary, the human eye works as light is received by the eye, passing through the cornea which bends the light. The light then passes through the lens to focus on the retina which turns the light into electrical signals which travel from the retina, to the optic nerve and finally into the brain which turns these signals into the images we see. Keep reading to learn more about how vision works and what the human eye is capable of.
What Parts of the Eye are Responsible for Vision?
The parts of the eye that are responsible for vision are the cornea, the iris, the pupil, the lens, the retina and the optic nerve. These parts work together to help humans see images by sending visual information obtained by the eye to the brain. The parts of the eye responsible for vision are listed below.
- Cornea: The cornea is the part of the eye that helps focus light. It is the clear outer layer found at the front of the eye.
- Iris: The iris is the coloured part of the eye which is located behind the cornea. The iris controls the amount of light that enters the eye through the pupil.
- Pupil: The pupil is the black circle in the centre of the eye and is responsible for the amount of light that enters the eye and is located in the iris.
- Lens: The lens, also known as the crystalline lens, is a transparent structure that helps the eye to focus light onto the retina.
- Retina: The retina is a structure in the eye found at the back of the eyeball. Its main function is to convert light that enters the eye into images that are then sent to the brain.
- Optic nerve: The optic nerve is part of both the eye and the body’s central nervous system. It transmits all visual information to the brain.
The below image is the anatomy of the eye and shows the different parts that are responsible for vision.
How Does the Eye Work with the Brain?
The eye and the brain work together to make vision possible. The brain is an integral part of how vision works as, according to Discovery Eye, the brain translates what we see into something we can understand. According to the National Eye Institute, this process works as cells in the eye called photoreceptors turn light that hits the retina into electrical signals which travel through the optic nerve and into the brain. Once the brain receives these signals, it turns them into images that humans see.
The brain is also very important in what we see as it flips the images the right way up. When light hits the retina, what we see is upside down, so the brain is responsible for turning the images right side up.
What is the Step-by-Step Process by Which the Human Eyes See?
The step-by-step process for how the human eye sees is as follows; the cornea allows light to enter the eye, the pupil adapts according to the intensity of light, the lens directs and concentrates the light onto the retina, the retina receives the light that is focused and the optic nerve carries visual information to the brain. The step-by-step process of seeing is listed below.
- The cornea allows light to enter the eye: The cornea is the part of the eye that helps light enter the eye. The cornea controls the amount of light entering the eye, focusing the light that is received.
- The pupil adapts according to the intensity of light: The pupil contracts and expands to let light in, adapting according to the intensity of the light.
- The lens directs and concentrates the light onto the retina: The lens works by directing and concentrating light onto the retina. The lens, also known as the crystalline lens, is the clear part of the eye located behind the iris.
- The retina receives the light that is focused: The retina is a layer of tissue at the back of the eye which receives light that is focused on the retina by the lens. The retina is the part of the eye that converts light into electrical impulses.
- The optic nerve carries visual information to the brain: The optic nerve is located at the back of the eye and is the part of the eye that carries visual information from the eye to the brain.
Light is crucial for the human eye to see as without light, we would not be able to see anything. According to The Physics Classroom, the human eye sees due to light from objects moving through space to reach our eyes.
1. The Cornea Allows Light to Enter the Eye
The cornea is located in the front of the eye, covering the iris, pupil and anterior chamber and is the part of the eye that allows light to enter the eye. The cornea is a clear, outer layer and, according to the Cleveland Clinic, it is made up of collagen and water. The cornea is the first contact light has with a person’s eye. And its main function is to control the amount of light entering the eye, focusing the light that is received. When light enters the cornea, it bends and refracts the light. Once light enters the eye through the cornea, it travels to the lens.
2. The Pupil Adapts According to the Intensity of Light
When light enters the eye, the pupil adapts by getting bigger or smaller according to the intensity of light. The pupil is a part of the eye which is the black circle located directly in the eye’s centre and is covered by the cornea and surrounded by the iris which is the coloured part of the eye. The pupil allows light to pass through so that it can be focused in the retina by the eyes’ lens and transferred into images. According to the National Eye Institute, the iris controls how much light the pupil lets into the eye.
3. The Lens Directs and Concentrates the Light onto the Retina
The lens is the next part of the eye that is responsible for vision and it works by directing and concentrating the light onto the retina. The lens, also known as the crystalline lens, is the clear part of the eye located behind the iris. According to the National Eye Institute, the lens works with the cornea to focus light so that it reaches the retina correctly. The lens receives the light of images upside down and as it is transferred to the brain, the optic nerve flips the image so it is right side up. The lens changes its shape due to its natural elasticity to shine received light directly to the retina, starting the process of transforming outside light into a perceivable image.
4. The Retina Receives the Light that is Focused
The retina is a layer of tissue at the back of the eye which receives light that is focused on the retina by the lens. According to the National Eye Institute, the retina is the part of the eye that converts light into electrical impulses. These impulses are then sent to the brain via the optic nerve, creating the images humans see. The retina is made up of two parts, the first is the macula which is integral in vision as it perceives up close and small details. The second is the peripheral retina which is responsible for peripheral vision which is the vision outside a person’s central vision.
5. The Optic Nerve Carries Visual Information to the Brain
The optic nerve is an essential part of sight which is made up of millions of nerve fibres and it carries visual information from the eye to the brain. The optic nerve is the largest sensory nerve in the eye and is part of the central nervous system, as described by the National Eye Institute. This long nerve extends from the back of the eye and connects directly to the brain. Once the retina has turned light into electrical signals, these are sent to the optic nerve which then travels to the brain where finally, the brain will turn the signals into images. The optic nerve is a critical part of what humans see as without it, no visual information would be received by the brain.
How Well Does the Human Eye See?
The human eyes can see very well in many aspects such as detail, distance and colour perception. In terms of distance, according to the Guinness World Record, the human eye can see at a distance of 275 miles which is approximately 443 kilometres. Most of the time, the distance at which we can see is interrupted by the horizon, meaning we could see further but due to the earth’s curvature, our sight is cut short.
How well the human eyes see can be affected by the health of the eye and a person’s visual acuity. Certain eye diseases can affect a person's vision, potentially leading to partial or complete vision loss. Some of these eye conditions include glaucoma, age-related macular degeneration, cataracts and diabetic retinopathy. In terms of visual acuity, this is the measurement of the sharpness and clarity of a person’s vision. Visual acuity may be diminished due to refractive errors such as nearsightedness, farsightedness or astigmatism.
Is the Human Eye More Precise Than a Camera?
It is difficult to determine whether the human eye is more precise than a camera as there are many aspects of vision and image capturing that can be compared. According to Cambridge in Colour, a learning community for photographers, there are three main differences between the human eye and a camera. The first is the angle of view, the second is detail and resolution and finally sensitivity and dynamic range.
One difference of note is how the eyes perceive detail and how a camera perceives detail. A camera detail is measured in megapixels which essentially describes how clear the image captured is. The human eye doesn't capture an image the same way a camera does as our mind doesn't see an image in megapixels, but rather in what is most memorable whether that is colours, textures or contrast. Cambridge in Colour describes this as the eyes taking a mental image with the detail being an indication of what was most interesting to the person.
What is the Best Vision Possible?
There is no definitive answer to what is the best vision possible although 20/20 vision is measured as normal vision so it can be inferred that a person with better than 20/20 vision has above-average vision. 20/20 is a measurement in feet of a person’s visual acuity which is the sharpness and clarity of their vision. The measurement is determined using a letter chart that is used in an eye test with an optometrist. 20/20 is not the best vision possible as people can have better than this measurement. For example, a person can have 20/15 vision which means they can see an object clearly at 20 feet what a person with 20/20 vision would need to be 15 feet away to see.
How Does Blue Light Affect How the Human Eye Sees?
Blue light does not directly affect how the human eye sees, rather there is some evidence that it may cause damage to the eyes. According to the University of California, extended exposure over time to blue light may cause damage to the eye’s retina cells, which could lead to the development of certain eye conditions such as age-related macular degeneration and cataracts. There is also research conducted by the National Eye Institute that suggests children's eyes absorb more blue light from digital devices, making them more at risk than adults.
Blue light glasses can be worn to potentially mitigate the effect of blue light as the lenses are designed to block a certain degree of blue light emitted from digital screens such as a computer, laptop or smartphone.
Can the Human Eye See Everything Around Us?
No, the human eye cannot see everything around us as there are certain limitations the eyes have. For example, we are unable to see bacteria without the help of a microscope and we cannot see radio waves. However, the human eye can see great distances depending on other factors such as light, the earth’s curvature and the health and visual acuity of a person’s eye.
What can we not See with our Human Eyes?
There are many limitations the human eyes have meaning there are certain things they cannot see. According to the University of Rochester, some of the limitations of the human eye include its light-gathering ability, the eye being unable to store images like a camera. The eyes are also limited in their frequency response meaning they can only see electromagnetic radiation in the visible wavelengths.
Are There Colours the Human Eye Cannot See?
Yes, there are colours that the human eye cannot see. According to the European Space Agency, there is a large amount of the spectrum of light that the human eye cannot see such as infrared and ultraviolet colours. The way the eyes perceive colour, as described by Pantone, is that colours are absorbed or reflected on the surface of objects, meaning objects do not inherently have colour. According to Pantone, it is estimated by researchers that the human eye can see approximately one million different colours.