Human Eye
The eye is the most important optical instrument that detects light and sends signals along the optic nerve to the brain.
It is an essential organ that gives us the ability to see. It allows light sensing, vision and differentiating among different colors. It is far more delicate than even the finest photographic camera designed so far. One of the remarkable qualities of the eye is the ability to observe distinctly the objects situated at widely different distances from the eye. This attribute of the eye is called the accommodation of the eye.
Human Eye Diagram
The figure systematically shows the components of the eye.
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Parts of the Human Eye
The human eye has a nearly spherical shape of diameter about an inch having various parts in such a small sphere are described below:
Cornea
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The front portion of the eye is more sharply curved and is covered by a transparent protective membrane called the cornea. It is this portion that is visible from outside.
Limbus: The limbus is the border of the cornea.
Sclera: The outer white part of the eye.
Aqueous Humor
There is a space filled with a transparent watery fluid similar to plasma behind the cornea called the aqueous humor.Crystalline Lens
The crystalline lens is held in the ciliary muscles and located behind the cornea. It is the name given to the natural lens that humans are born with.Ciliary Muscles
Ciliary muscles are the small muscles that are attached to the crystalline lens that can make the lens change shape that allow the eyes to focus on near or far objects.Iris
There is a muscular diaphragm in between the aqueous humor and the lens, called the iris. The iris is the colored part of the eye that we can see.Pupil
A small hole in an iris eye with a circular aperture is called the pupil. The pupil appears black as the light goes inside it has no chance of reflecting or coming back outside.Retina
The light entering the eye forms an image on the retina that covers the inside of the near part of the eyeball.Vitreous Humor
The space between the lens and the retina is filled with a liquid called vitreous humor.Optic Nerve
The optic nerve is a part of the human eye that is located behind the eye. It is the second cranial nerve that helps in carrying the vision of the eye and reflects it to the human brain. It transfers the electric impulses from the retina and projects them in the cortex of the human brain. It reaches the brain through the optic disk and that particular point is called the blind spot.Optic Axis
The line joining the center of the cornea to the center of the lens is called the optic axis.
Functions of All Parts of the Eye
Ciliary Muscles
The shape i.e. the curvature and the focal length of the crystalline lens can be modified by the ciliary muscles.Crystalline Lens
The image of an external object is formed by the crystalline lens on the retina.
The main function of a lens is to maintain the accommodation of the eye, maintain its own clarity, and refract the light.Retina
The retina contains about 125 million receptors called the rods and cones that can sense the light intensity and color respectively and about one million optic-nerve fiber which transmits the information to the brain. The least sensitive part of the retina is called the blind spot.Iris
The function of an iris is to adjust and allow a suitable quantity of light to the eye.Cornea
The front transparent hard outer part of the eye protects the inner delicate parts of the eye.
Myopia and Hypermetropia
Myopia is a condition of damage to vision. This condition is caused when the image of the object we see forms behind the retina as the curvature of the retina increases and it is difficult to see distant objects. This condition is also known as short-sightedness and can be rectified by using diverging lenses recommended by an optician.
Hypermetropia is also known as long-sightedness is also caused when the vision of our eye is affected. In this condition, the image of the object we see forms in front of the retina, and this is caused when the structure of the eye is affected. One can not see objects placed closer to the eye in this condition as the focal length increases for such people. Some of the structural defects which might lead to this case are small eyeball size, non-circular lenses, weak ciliary muscles, defective blood vessels in the retina, change in the refractive index of the eye when the position of the lens is affected.
What is the Function of Ciliary Muscles?
Case 1: When the eye is focused on the distant object
The ciliary muscles loosen up so that the focal length of the eye-lens has its maximum value which is equal to its distance from the retina.
Case 2: When the eye is focused on the closer object
The ciliary muscles become tense and the lens cannot curve enough to focus the image on the retina. The focal length of the lens decreases. Therefore, the image becomes blurred. However, the ciliary muscles adjust the focal length in such a way that the image is again formed on the retina and we see the image clearly. Such a process of adjusting the focal length to make an image visible clearly is called the accommodation.
Do you know?
The least distance of vision (d) for a normal eye is 25 cm (range of vision).
The human eye can distinguish about 10 million different colors approximately.
The human eye blinks at a mean of 4,200,000 times a year.
The eye is made of 10 million working parts and it weighs just 0.25-ounces.
The eyes remain the same size throughout life.
Eyes can process about 36,000 pieces of information in an hour.
Know the functions of the human eye better by logging into Vedantu’s official website. Learn what the experts have to say about this topic. Develop your conceptual foundation regarding the different parts of the human eye and their specific functions to answer questions aptly.
FAQs on Human Eye Function
1. What is the main function of the human eye?
The primary function of the human eye is to act as an optical instrument that detects light from the environment and converts it into electrochemical impulses. These impulses are then sent to the brain via the optic nerve, allowing us to perceive images, differentiate colours, and gauge distances, which we interpret as vision.
2. What are the specific functions of the cornea, iris, and lens?
Each part of the eye plays a crucial role in the process of vision. Here are the functions of three key components:
- Cornea: This is the transparent, outermost layer at the front of the eye. Its main function is to refract, or bend, most of the light that enters the eye, providing the majority of the eye's focusing power. It also serves as a protective barrier.
- Iris: This is the coloured part of the eye. Its function is to control the size of the pupil, thereby regulating the amount of light that reaches the retina. In bright light, the iris constricts the pupil, and in dim light, it dilates it.
- Crystalline Lens: Located behind the iris, the lens fine-tunes the focus of light onto the retina. By changing its shape, a process called accommodation, it allows the eye to focus on objects at various distances.
3. How does the human eye's power of accommodation work?
The power of accommodation is the eye's ability to adjust its focal length to see both near and distant objects clearly. This is achieved by the ciliary muscles, which are attached to the crystalline lens. When looking at a distant object, the ciliary muscles relax, making the lens thinner and increasing its focal length. To focus on a nearby object, the ciliary muscles contract, causing the lens to become thicker and rounder, which decreases its focal length.
4. How do the retina and optic nerve work together to create vision?
The retina and optic nerve are essential for converting light into a signal the brain can understand. The retina, located at the back of the eye, contains millions of light-sensitive cells called rods and cones. When light is focused onto the retina, these cells generate electrical signals. The optic nerve then acts as a data cable, collecting these signals from the retina and transmitting them to the brain. The brain processes these signals to interpret them as a visual image.
5. What is the main difference between Myopia and Hypermetropia?
Myopia (short-sightedness) and Hypermetropia (long-sightedness) are common refractive errors that affect how images are focused in the eye. The key difference lies in where the image is formed relative to the retina:
- In Myopia, the eye focuses the image of a distant object in front of the retina, either because the eyeball is too long or the cornea/lens has too much focusing power. This makes distant objects appear blurry.
- In Hypermetropia, the eye focuses the image of a nearby object behind the retina, often because the eyeball is too short or the lens has too little focusing power. This causes nearby objects to seem blurry.
6. Why do we have two eyes, and what visual advantage does this provide?
Having two eyes, known as binocular vision, provides two significant advantages over having just one. Firstly, it gives us a wider field of view, allowing us to see more of our surroundings at once. Secondly, and more importantly, it enables stereoscopic vision or depth perception. Each eye captures a slightly different image, and the brain fuses these two images into a single three-dimensional one, which allows us to judge distances and perceive depth much more accurately.
7. Why does a 'blind spot' exist in our vision, and why are we usually unaware of it?
A blind spot exists in each eye at the point where the optic nerve exits the back of the eye to connect to the brain. This specific area, called the optic disc, lacks photoreceptor cells (rods and cones), so it cannot detect light. We are typically unaware of this blind spot for two reasons: firstly, the visual field of our other eye covers the blind spot, and secondly, our brain cleverly 'fills in' the missing information based on the surrounding image.
8. What are some examples of practical ways to care for our eyes?
Maintaining good eye health is crucial for preserving vision. Some practical examples include:
- Eating a balanced diet rich in vitamins A, C, and E, and nutrients like omega-3 fatty acids, found in green leafy vegetables, carrots, and fish.
- Taking regular breaks from screens using the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds.
- Ensuring adequate sleep, as it allows the eyes to rest and repair.
- Wearing sunglasses to protect your eyes from harmful UV radiation.
