Chapter 11: Human Eye and Colourful World Revision Notes
- The human eye is a magnificent natural gift to the human body. The human eye has a roughly spherical shape with a diameter of 2.5 cm.
Human Eye Components:
- Cornea: The cornea is the eye’s protective and front layer. A translucent membrane is used to create it. The cornea allows light to enter the eye.
- Iris is the name given to a dark and colourful muscular diaphragm. It is in charge of the eye’s colour.
- Iris Pupil: A little circular hole at the iris’s centre. It adjusts the size of the iris to control the quantity of light that enters the eye.
- Ciliary Muscles: These muscles keep the eye lens in place. The size of the eye lens is altered.
- The eye lens is a convex lens formed of a translucent jelly-like substance.
- The retina is the eye’s screen. On the retina, a genuine and inverted picture form.
- Color-sensitive rods and cone-shaped cells are called rods and cones. Rods are in charge of vision in low light, whereas cones are in charge of colour perception.
- The optic nerve turns vision information into an electric signal and transmits it to the brain.
- The blind spot is the area between the optic nerve and the retina where there are no rods and cones cells. It is unaffected by light.
- Near Point: The point closest to the eye where the eye can see well without effort is referred to as the near point. It is 25 centimetres for a typical eye.
- The farthest point beyond which the eye can clearly perceive the object is referred to as the far point. It seems to be infinite to the naked eye.
- The range of vision refers to the distance between the near and distant points of the eye.
The capacity of the eye to perceive both close and far things clearly is referred to as power of accommodation.
- Nearsightedness (myopia) is a condition in which the eye is unable to view far away objects clearly but can see close objects properly.
Reason:As the size of the eyeball grows larger,Because to the cornea’s extreme curvature,
Due to an increase in eye lens power (or a decrease in focus length).
It is remedied by a concave lens of appropriate focal length.
Hypermetropia (farsightedness) is a defect in which the eye is unable to view local items clearly but can see far away objects clearly.
Reason. Due to a reduction in the size of the eyeball. Because the eye lens’s power (or focal length) has decreased.
It is remedied by employing a convex lens with a long enough focal length.
Dispersion of Light: Dispersion is the splitting of white light into seven colours. Consider the development of the Rainbow (VIBGYOR). The violet colour deviates the greatest, while the red colour deviates the least.
One of the most significant and sensitive sense organs is the human eye. It allows us to view the beautiful environment and colours that surround us.
The eyeball has a diameter of around 2.3 cm and is roughly spherical in form.
The outer surface of the cornea is where the majority of the refraction for light rays entering the eye happens.
The crystalline lens only allows for finer focal length adjustments, which is necessary for focusing.
The human eye is made up of the following components:
- Cornea: The spherical translucent membrane that covers the front of the eye.
- The coloured diaphragm between the cornea and the lens is known as the iris.
- Pupil: The iris’s tiny hole.
- It is a transparent lens constructed of a jelly-like substance.
- Ciliary muscles are the muscles that keep the lens in place.
- The rear surface of the eye is known as the retina.
- The place where the optic nerve exits the eye is known as a blind spot. The brain does not receive a picture created at this moment.
- Between the cornea and the lens is a clear liquid area called the aqueous humour.
- Vitreous humour: Another liquid called vitreous humour fills the gap between the eye lens and the retina.
- The picture on the retina of the eye is created by sequential refractions at the cornea, aqueous fluid, lens, and vitreous humour. The optic nerve subsequently transmits electrical impulses to the brain, where they are interpreted. The yellow area is the most sensitive to detail in excellent light, and the picture is immediately created there.
- Accommodation refers to the eye’s capacity to concentrate on both near and far objects by shifting its focal length, or the ability of the ciliary muscles to modify the focal length of the eye lens.
- Eye Defects: Despite being one of the most spectacular organs in the body, the eye can have a variety of defects that can frequently be addressed with eyeglasses, contact lenses, or surgery. I Hypermetropia (long sightedness), (ii) Myopia (shortsightedness), (iii) Astigmatism, and (iv) Presbyopia are the numerous problems that can affect an eye.
- Long sightedness, also known as hypermetropia, is a condition in which a person can see far objects clearly but not adjacent items. The closest point of this flaw is more than 25 cm distant. A convex lens of appropriate power is used to treat hypermetropia (far sightedness, in which the picture of adjacent objects is focused beyond the retina). With ageing, the eye’s ability to accommodate changes diminishes.
- Hypermetropia is caused by one of two factors: either the hyperopic eyeball is too short or the hyperopic eyeball is too long.
- The ciliary muscle is unable to modify the shape of the lens sufficiently to adequately focus the picture, resulting in an increase in the focal length of the eye lens.
- Myopia, often known as short sightedness or close sightedness, is a condition in which a person can see local items clearly but not far distant ones. A concave lens of appropriate power is used to rectify myopia (short sightedness, in which the picture of distant objects is focused before the retina).
- The following factors contribute to this defect: either the eyeball is longer than usual, or the lens’ maximum focal length (due to excessive corneal curvature) is insufficient to generate a well formed picture on the retina.
- A person may also suffer from astigmatism, a condition in which light from a single point generates a line picture on the retina. A person with this condition is unable to see in both directions equally well, i.e., he is unable to perceive both vertical and horizontal lines at the same time. When the cornea, crystalline lens, or both are not exactly spherical, this condition occurs. Astigmatism can be remedied with cylindrical lenses that have distinct curvatures in two mutually perpendicular orientations.
- When a person suffers from both myopia and hypermetropia, bifocal lenses are used in his corrective spectacles. The upper part of the lens is concave for distance vision, while the lower half is convex for reading.
- Presbyopia is a vision problem that makes it difficult for an elderly person to read and write comfortably. Presbyopia is sometimes known as aged sight for this reason.
- An elderly person must use spectacles with a convex lens of appropriate focal length or power to correct Presbyopia, as previously mentioned.
- Hypermetropia is caused by a reduction in the length of the eyeball or an increase in the focal length of the eye lens. Presbyopia, on the other hand, is caused by an increase in the focal length of the eye lens. In Presbyopia, the eyeball is of normal length.
- The eye’s eyesight deteriorates, perhaps to the point of utter blindness. Cataract surgery, or the removal of the eye lens and replacement with a lens of appropriate focal length, solves the problem.
- Because a human has a horizontal field of view of around 150° with one eye and about 180° with two eyes, we require two eyes. As a result, having two eyes gives us a greater horizontal range of view.
- The world seems flat, or two-dimensional, when viewed through one eye. The view is three dimensional with two eyes, i.e., a dimension of depth is added to our vision.
- Because our two eyes are a few millimetres apart, each sees a slightly different image. Our brain blends the two viewpoints into one, allowing us to determine the distance between the objects we perceive.
- One pair of our eyes can provide vision to two corneal blind persons if we donate them after we die. Donors of eyes might be of any gender or age. People with diabetes, hypertension, asthma, and other non-communicable illnesses are eligible to donate their eyes. People who wear spectacles or have had cataract surgery can also donate their eyes.
- The near point of the eye, also known as the least distance of distinct vision, is the shortest distance at which the eye can see objects clearly without exertion. It’s roughly 25 centimetres for a young adult with normal vision.
- The picture of an item remains on the retina for 1/16 second after the thing has been removed. A movie camera’s sequence of still images is displayed on a screen at a rate of roughly 24 images per second or higher. The consecutive pictures on the screen appear to blend easily into one another, giving us the sense of moving images.
- The retina of the eye has a huge number of light sensitive cells of two types: rod shaped cells that respond to light brightness or intensity, and cone shaped cells that respond to light colour. We can discriminate between distinct colours using thus/cone shaped cells.
- When a person’s vision is normal but he can’t distinguish between different colours, he is said to be colour blind. Color blindness is a hereditary disease that is passed down through the generations. There is currently no remedy for colour blindness.
- The far point of the eye is the furthest point beyond which a short-sighted eye can see well. The distant point is infinity for a normal eye.
- The near point of the eye refers to the farthest point to which a long-sighted eye can see well. The near point of an adult’s normal human eye is roughly 25 cm from the eye.
- Least cfistance of distinct vision: The legist distance of distinct vision is the shortest distance at which an eye can see well; it is usually indicated as D. The distance between the eye and its near point is the shortest distance of clear vision. This distance is around 25 cm for a typical human eye.
- The distance between the distant and near points of the eye is referred to as the eye’s range of vision.
- The violet light bends the greatest and the red light bends the least when white light passes through a prism. When white light passes through a glass prism, it splits into its seven constituent colours, which is known as dispersion. The visible spectrum is the band of seven colours acquired in this way.
- Violet, indigo, blue, green, yellow, orange, and red are the seven colours of white light. The abbreviation VIBGYOR is used to recall it.
- The first person to use a prism to get a spectrum of sunlight was Isaac Newton.
- When white light is split by a prism, we get a range of various colours called the spectrum.
- Dispersion is caused by the fact that each colour has its unique wavelength/frequency. In air/vacuum, different colours travel at the same speed. However, their speeds in refracting media like as glass differ. As a result, the refractive index of the medium varies depending on the colour. As a result, various colours pass through the prism with varying deviations. As a result, the prism emits distinct colours in different directions.
- In a vacuum, the speed of light is the same for all wavelengths, however in a solid body, the speed is variable for various wavelengths.
- Red light travels the fastest in any medium other than air/vacuum, whereas violet light travels the slowest.
- The section of the spectrum that the human eye can perceive is the most familiar kind of electromagnetic radiation. The rearranging of electrons in atoms and molecules produces light. Colors ranging from violet (= 4 x 10-7 m) to red (= 7 x 10-7 m) are used to classify visible light wavelengths. The sensitivity of the eye is a function of wavelength, with a maximum sensitivity at a wavelength of roughly 5.6 x 10-7 m. (yellow-green).
- When white light is passed through two ideptical prisms placed side by side with their refracting edges pointing in opposite directions, the first prism disperses the light into seven colours, while the second prism recombines the seven colours into white light. As a result, the light that emerges from the second prism is white.
- The dispersion of light by small droplets of water acting as prisms creates a rainbow.
- Twinkling stars, early sunrises, and late sunsets are all caused by atmospheric refraction.
- The blue colour of the sky and the reddening of the Sun at sunrise and sunset are caused by light scattering.