[Physics Class Notes] on The Human Eye Pdf for Exam

The human eye is an essential organ, which interacts with light and is necessary for the sense of sight or vision. There are two kinds of cells in the eye i.e. rods and cones.

 

Conscious light perception, colour differentiation and perception of depth are done by these cells. The human eye can differentiate between about 10 million colors, and it can also detect a single photo. The human eye is a part of the sensory nervous system.

The eyes of all mammals have a non-image-forming photosensitive ganglion in the retina which receives light, adjusts the size of the pupil, regulates the supply of melatonin hormones, and also entertains the body clock.

We can be aware and see beautiful things around our environment, thanks to our vision. We learn 80% of what we know through our senses of sight. The way your eyes work is similar to how a camera does. They focus on the light that’s reflected in their eyes.

The cornea, iris, pupil, and lens make up the front of the eye, which focuses the image onto the retina. The light-sensitive membrane that covers the back of the eye is known as the retina. This membrane is made up of millions of nerve cells that clump together behind the eye to form the optic nerve, a huge nerve.

The Human Eye

The eye is one of the most significant and sophisticated sense organs that we have as humans. It aids in object visualization as well as the perception of light, colour, and depth. Furthermore, these sense organs are comparable to cameras in that they assist humans in seeing objects when light from the outside enters them. That so, learning about the structure and operation of the human eye is fascinating. It also assists us in comprehending the operation of a camera.

Six muscles are in the eye. They are responsible for controlling the movement of the eye. The most common kinds of muscles that are in the eye are the lateral rectus, medial rectus, inferior oblique, or superior rectus.

Parts of the Human Eye

• Pupil: The pupil is a small opening in the iris. The iris controls the size of the pupil. The pupil’s function is to adjust the amount of light entering the eye.

• Sclera: The outer covering of the eye is called the sclera. It is a protective tough white layer (white part of the eye).

• Cornea: The transparent part in front of the sclera is called the cornea. Light enters the eye through the cornea.

• Iris: It is a dark, muscular tissue and ring-like structure present behind the cornea. The colour of the eye is due to the colour of the iris. The iris regulates the amount and intensity of light entering the eyes by adjusting the size of the iris.

• Retina: It is the light-sensitive layer that consists of nerve cells. Its function is to convert the images formed by the lens into electrical impulses. These electrical impulses are then transmitted through optic nerves to the brain.

• Lens: The transparent portion situated behind the pupil is called the lens. The lens alters the shape to focus light on the retina, with the help of ciliary muscles. It becomes small to focus on objects at a distance and becomes big to focus on nearby objects.

• Optic Nerves:  You can find two types of optic nerves, which are cones and rods.

1. Cones: Cones are the nerve cells that are more sensitive to bright light. Cones help in central and colour vision.

2. Rods: Rods are the nerve cells that are more sensitive to dim lights. Rodes help in peripheral vision.

There are no sensory nerve cells at the junction of the optic nerve and retina. Therefore, no vision is possible at this point, and it’s called the blind spot.

Working of the Human Eye

The human eye operates similar to a digital camera in several ways:

• Light focuses mainly on the cornea, which acts like a camera lens.

• The iris controls the light that reaches the eye by adjusting the size of the pupil, and thus it functions like the diaphragm of a camera.

• The lens of the eye is located behind the pupil, and it focuses light. This lens helps the eye to automatically focus on near and distant objects, and also the approaching objects, like an autofocus camera lens.

• The cornea and lens focus light to reach the retina, which is a light-sensitive zone present on the inner lining of the back of the eye.

• The retina converts optical illusion images into electronic signals, and thus it acts as an electronic image sensor of a digital camera. These electric signals are then transmitted by the optic nerve to the visual cortex, which is responsible for the sense of sight.

The Function of the Human Eye

Human eyes are a specialized sense organ that is capable of receiving visual images, thereby producing the sense of sight in us. The eye receives direct oxygen through the aqueous humor. The aqueous humor nourishes the cornea, lens, and iris, by carrying nutrients, removing wastes materials excreted by the lens, and maintaining the shape of the eye. The aqueous humor is responsible for providing shape to the eye. It must be clear to function properly.

The Lens of the eye

The crystalline lens, also known as the lens of the eye, is a crucial component of the eye’s structure that allows the eye to concentrate on objects at various distances. It is situated in front of the vitreous body, behind the iris.

The lens seems to be an extended spherical — known as an ellipsoid — that resembles a deflated ball in its natural form. Adult lenses are roughly 10 mm across and 4 mm from front to rear in size.

Proteins make up virtually entirely of the lens. Proteins make up almost 60% of the lens of the eye, which is more than any other physiological tissue in terms of protein concentration. Because the tissue is translucent, light can easily enter the eye. It’s also bendable, allowing it to change shape and bend light to appropriately focus on the retina.

What is the Work of the Lens in the Human Eye?

The lens is a transparent flexible tissue located directly behind the iris and the pupil. The lens’ main job is to bend and concentrate light in order to create a sharp image. When concentrating on distant objects, the lens uses ciliary muscles to extend and thin out, and when focusing on close objects, the lens shrinks and thickens. The function of the lens is to focus light and images on the retina. The cornea and the lens are responsible for focusing the ima
ge in the retina.

Due to the elastic & flexible nature of the lens, it can change its curved shape to focus on nearby or distant objects depending on the need. The lens provides around 25-35 % of the total focusing power of the eye. The lens is attached to the ciliary muscles, which contracts and releases in order to change the shape of the lens and also its curvature.

The lens becomes oval-shaped to focus on near objects. The lens becomes elongated (or stretched) to focus on objects located at a far distance. When light enters the eye, the lens bends and focuses the light directly on the retina, producing the sharpest image possible.

On the retina, the crystalline lens projects a focused image. However, the projected image appears inverted at first (either upside down or reversed). The brain will flip the image back to normal when the image is given to it via the optic nerve.

The ciliary body is necessary for the lens to work properly. While the ciliary muscles allow the lens to change shape in order to focus, the lens is held in place by zonular fibres, or zonules, which are attached to the ciliary body. Aqueous humour is produced by the ciliary body, which keeps the lens healthy and functional.

Rather than nerves or blood flow, the lens gets its energy and is washed from the aqueous fluid. The aqueous humour is a transparent fluid that passes through the eye and subsequently drains through the trabecular meshwork.

 

Do You Know?

The human eye is blind for about 40 minutes every day. This is because of Saccadic masking; it is a way of the body to reduce motion blur while the object and eyes move. 20/20 is a normal vision and it’s not a perfect vision.

 

It means if a normal person can see an object at a distance of 20 feet, the test subject can also see the object at 20 feet. Hence the article covers all the necessary information related to the human eye. It discusses parts of the human eye and its function and working etc. It will be helpful for the students to understand the functioning of the human eye.