Jasmine Grover Content Strategy Manager
Content Strategy Manager
Human eye is the most valuable and sensitive organ of the human body. It allows us to see the beautiful environment and colors that surround us. We can identify items to some extent by their scent, taste, sound, or touch when we close our eyes. Closed eyes, on the other hand, make it impossible to detect colors. As a result, the human eye is the most important of all sense organs because it allows us to perceive the wonderful, colorful world around us. The human eye functions similarly to a camera. Its lens system creates an image on the retina, a light-sensitive screen. The cornea is a thin membrane that allows light to enter the eye. The translucent protrusion on the front surface of the eyeball is formed by it. The eyeball has a diameter of around 2.3 cm and is roughly spherical in shape. The outer surface of the cornea is where the majority of the refraction of light rays entering the eye occurs. The crystalline lens merely allows for finer focal length adjustments to concentrate objects at various distances on the retina. Behind the cornea is a structure called the iris. Iris is a black muscular diaphragm that regulates pupil size.
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Read Also: Light-Reflection and Refraction Revision Notes
Parts of the human eye
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Cornea: The white portion of the eye that permits light to pass through. It acts as a portal to the outside world.
Iris: It is a portion of the eye that is colored. It keeps the pupil open and adjusts the size of the pupil in response to light intensity.
Pupil: It has a dark tint and absorbs all light rays that strike it. When the light intensity is great, it becomes restricted. When the intensity of light is low, it expands.
Retina: The image is created on the retina of the eye.
The retina is made up of two cells of different types-
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Color-responsive cells are known as cone cells.
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Rod cells are the cells that respond to light intensity.
Yellow spot: It is a point on the retina where the image formation is the clearest.
Suspensory ligament: The suspensory ligament supports the ciliary muscle and lens.
Suspensory ligaments are elastic-like structures that serve to hold the lens in place in the eye.
The ciliary muscles are attached to the other end of the suspensory ligament.
Ciliary Muscles: Ciliary muscles surround the lens and determine its shape. By contracting or relaxing, they assist in altering the focal length of the lens.
The bulk of the eye is made up of vitreous humor, which is located behind the lens.
It's a viscous, transparent, jelly-like fluid that helps keep the eye's form while also refracting light onto the retina.
The video below explains this:
Human Eye One Shot Detailed Video Explanation:
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| The Human Eye and The Colourful World Revision Notes | The Human Eye and The Colourful World Important Questions |
Working of the eye
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The human eye functions similar to a camera. The light reflects off the objects and enters the eyeball through the cornea, a transport layer of tissue in the eye. The cornea bends light rays as they pass through the pupil, which is the black opening in the middle of the colored part of the eye. The light is adjusted and goes through the natural crystalline lens of the eye. The resulting image is actual, tiny, and reversed because the eye lens is convex in nature. The retina creates this image. These rays are converted into electrical signals by the retina, which is then sent to the brain via the optic nerve. The brain interprets the information it receives, allowing us to see.
Role of Iris and Pupil
The amount of light required to expose the film in the camera's back determines whether the shutter closes or opens. The eye, like the shutter on a camera, works in the same way. The iris and pupil regulate the amount of light that enters the rear of the eye. The iris has muscles that allow the pupil to expand and contract. The iris controls the amount of light that enters the eye by altering the pupil opening size. The iris contracts, reducing the size of the pupil, when the number of light rays reaching the eye is high. As a result, the intensity of light will be reduced (just a tiny amount of light will pass through the pupil), protecting our eyes from injury. If the intensity of the incident light is low, the iris widens and the pupil dilates or expands to allow enough light to enter the eye, allowing us to see the image clearly. The iris keeps track of the amount of light that enters our eyes by adjusting the pupil size.
Power of Accommodation
The eye lens, which is made up of a fibrous jelly-like substance, plays a vital function; also, the curvature of the eye lens affects the focal length. The lens shrinks and thins when the muscles relax; as a result, its focal length increases in this posture, allowing us to view distant objects clearly. When you look at an item that is closer to your eye, however, the ciliary muscles contract, causing the curvature of the eye lens to increase and the eye lens to thicken. The focus length of the eye lens shortens in this situation, allowing us to see nearby objects clearly. Accommodation refers to the eye’s ability to change its focal length. Furthermore, the eye lens's focal length cannot be reduced below a specified minimum. This is why we can't read a book that's too close to our eyes; instead, we must keep a specific distance. The object must be kept at a distance of around 25 cm from the eyes to see it comfortably and clearly. The farthest point, on the other hand, has no limit; the human eye can see infinity, including the moon, stars, and other celestial bodies.
Defects of Vision
- Myopia or near-sightedness: Myopia is also referred to as near-sightedness. Myopia affects a person's ability to see adjacent objects clearly but not distant items. The image of a distant object is created in front of the retina rather than at the retina in a myopic eye. Myopia may arise because of elongation of the eyeball or excessive curvature of the eye lens. A concave lens of suitable power can be used to correct this vision defect.
- Hypermetropia or farsightedness: Far-sightedness is another name for hypermetropia. Hypermetropia is a condition in which a person can see distant items clearly but not nearer items. The near point is further away from the standard near the point of 25cm in this scenario. Hypermetropia can occur when the focal length of the eye lens is too long, or when the eyeball is too small. A convex lens of suitable power can be used to correct this vision defect.
- Presbyopia: Presbyopia is a vision issue caused as the ciliary muscles gradually weaken and the eye lens becomes less flexible. Some persons have both myopia and hypermetropia; this type of vision problem is remedied using bifocal lenses. Concave and convex lenses are two types of bifocal lenses that are commonly used.
Read More The Human Eye and The Colourful World Important Questions
Frequently Asked Questions (FAQs)
Ques. What exactly does the term "accommodation power" imply?(1 mark)
Ans. The ability of the eye's lens to change its focal length to clearly concentrate rays from far away as well as close objects on the retina is known as the eye's capability of accommodation.
Ques. A person with a myopic eye is unable to distinguish items beyond 1.2 meters. What form of the corrective lens should be used to restore proper vision?(1 mark)
Ans. To restore adequate vision, a person with a myopic eye should use a concave lens with a focal length of 1.2 m.
Ques. What is the far point and near point of the human eye with normal vision?(1 mark)
Ans. The near point of the eye is the shortest distance between an object and the eye at which it may be viewed clearly without strain. This distance is 25 cm for a regular person's eye.
The far point of the eye refers to the distance at which the eye can clearly see objects. Infinity is the distant point of a regular person's eye.
Ques. What will be the color of the sky, when it is observed from a place in the absence of any atmosphere? Why?(1 mark)
Ans. The color of the sky, when it is observed from a place in the absence of any atmosphere, will be black. The reason for that is as there is no atmosphere there will be no scattering of light.
Ques. Explain why the planets do not twinkle?(1 mark)
Ans. Planets, unlike stars, do not twinkle. Stars are so far away that they appear in the night sky as pinpoints of light, even when viewed through a telescope. Because all of the light comes from a single source, its path is extremely vulnerable to atmospheric interference (i.e., their light is easily diffracted).
Ques. Why does the Sun appear to be reddish early in the morning during sunrise or during sunset?(1 mark)
Ans. Before reaching the observer, white light from the sun must travel a greater distance through the atmosphere. During this time, all other colored lights scatter, leaving just the red-colored light to reach the viewer. As a result, during sunrise and sunset, the sun appears reddish.
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