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Human Eye

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Light may be reasonable energy referred to as nonparticulate radiation. This way of energy is additionally employed in x-ray machines, microwave ovens, and radios. The nonparticulate radiation that we can see is termed actinic rays. Completely different sources turn out different styles of light-weight. The light-weight is sometimes thought of to be the visible part of the spectrum. However, in physics, light-weight may be outlined as all parts of the magnetism scale, together with invisible forms like infrared, ultraviolet, X-rays, radio waves, and more. At the rear of our eye may be a sensitive sheet of nerves referred to as the membrane. These nerves will notice light weight once it strikes the membrane. Our eye forms a picture on the membrane. This image is sort of a tiny image of what you’re staring at. The human eye and brain translate light-weight into color. Light-weight receptors intervals the attention transmit messages to the brain, which produces the acquainted sensations of color. By varying, the quantity of red, inexperienced, and blue light-weight, all the colors within the color spectrum may be created. Light-weight is nonparticulate radiation that has the properties of waves. The spectrum may be divided into many bands that supported the wavelength. As we’ve got mentioned before, actinic ray represents a slim cluster of wavelengths between concerning 380 nm and 730 nm. As we know the world is largely known through senses and the sense of sight is one of the most important senses. It is only that we see it when the light from an object enters our eyes. The light might have been either reflected by the object or emitted by it. 

The light energy enables us to see. Such as the Sunlight is emitted from a source. The word generally refers to visible light, which is observable to the human eye and is accountable for the sense of vision.

What happens when light falls on a mirror?

We know that light is a form of energy that is responsible for the sense of sight in the human eyes. Light can be called radiation that is emitted, reflected, or absorbed by different objects. A mirror is a glass with a shiny surface. It is reflected when light falls on a mirror. Hence, a mirror alters the way of light that falls upon it.

The human eye may be a spherically formed sense organ (diameter concerning 2.3 cm) that offers the sense of sight and helps North American countries understand colors and depth.

  • Eyes area unit sensory organs that enable North American countries to visualize things gift within the surroundings.
  • The eyes absorb the sunshine rays and kind a visible image and rework this data of the image to the brain.
  • The eye encompasses a spherical structure that is named the eyeballs. The eyeballs area unit is hooked up to the attention socket and the varied muscles area unit connected to them is known as the attention muscles. These area unit muscles that enable the movement of the eyeballs.
  • The eyes area unit is protected with eyelids. They stop associate degrees far more than lightweight and mud to enter the eyes and so save the eyes from any outer objects.

Define Human Eye:

The human eye is the most significant organ of our body that is an associate device that is our organ of signs. The human eye is sort of a camera. The Eyeball of the human eye is spherical. The diameter of the eyeball is 2.3 cm. Though there’s a marginal distinction in size in some individuals. It consists of a troublesome fibrous membrane known as a sclerotic coat that protects the interior components of the eye.

The eye encompasses a spherical structure that’s named the eyeballs. The eyeballs unit is attached to the eye socket and the varied muscles unit connected to them is called the eye muscles. These unit muscles change the movement of the eyeballs. The eyes unit is protected with eyelids. They stop associating way more than light and dust to enter the eyes and then save the eyes from any outer objects.

Function of the Human Eye

The eye may be a sensory organ. The eyes absorb the light rays and type an obvious image and makeover this information of the image to the brain. It collects light from the noticeable world around us and changes it into nerve impulses. The optic tract transmits these signals to the brain, which forms a picture therefore thereby providing sight.

Different Parts of the eye:

Cornea- It’s a clear covering gift on the outer facet of the eyes. It consists of six layers. Tear fluid covers the tissue layer and protects the attention.

Iris- It’s a dark-colored musculature gift within the center of the tissue layer. The Iris consists of a little gap decision Pupil through that the sunshine enters into the attention. The Iris has vibrant pigments like gray, blue, black, green, brown, etc. the number of sunshine that enters the attention is controlled by the Iris. In alternative words, Iris controls the Pupil.

Lens- It’s sort of a sphere of the liquid gift within the attention. The attention lens is found behind the Pupil which helps in the formation of a picture within the eye.

Membrane- Retina may be a layer settled behind the lens at the rear of the attention. The attention lens focuses the sunshine that enters the attention over the membrane. The membrane consists of various Nerve cells that perform different tasks. There are unit sensory cells that discover lightweight. They then rework that data into associate degree electrical impulse. These electrical impulses are units sent to the brain via the optic tract. Two sorts of vision cells within the membrane are:

  • Rods or chopsticks- They get activated in darkly or dim-light and are also liable for light-dark vision. They secrete a protein called rhodopsin which helps in light-dark vision.
  • Cones- They are photoreceptor cells in the retina and the protein iodopsin present in it helps in bright-light vision.

Vitreous Chamber- The inner area of the eyeball known as the clear vitreous chamber consists of a gel-like substance. This substance maintains the proper pressure within the eye and maintains the steadiness of the eyeball.

Blindspot- There’s a degree within the eye settled at the junction of the membrane and also the optic tract wherever no sensory cells area unit gift. This spot is thus known as the blind spot because it doesn’t support any vision.

Persistence of image on the membrane:

  • The image that’s shaped on the membrane persists for 1/16th of a second.
  • Therefore, if one tries to maneuver sixteen still pictures per second of a moving object ahead of our eye it seems as if the thing is moving. This is often however animation films and films work. They are a set of separate photos that are enraptured during a sequence.
  • However, this movement is thus quick, around twenty-four photos during a second, that’s why it seems as if they’re moving.

Range of vision of a standard human eye

The human eye, is an incredible instrument in humans. The human eye reacts with lightweight and permits us to examine the earth. The primary step within the formation of a picture in our eyes is passing lightweight through the tissue layer. The pupil of the attention permits the sunshine to enter the attention and therefore the iris controls the quantity of sunshine allowed to enter by the pupil of the attention. The sunshine then passes through the lens of the attention so the sunshine hits the tissue layer of our eyes. Within the human eye, the image is created on the tissue layer, and therefore the image formed is inverted. The inverted image is corrected by our brain by exploiting electrical signals from the tissue layer to the brain.

For a standard human eye, the variance of vision describes the variance of distance that human eyes will see the associate object clearly. For someone to visualize an associate object with a transparent vision, the image of that object should fall accurately on the tissue layer. This suggests that the space of the image should be similar to that of lens-to tissue layer distance. However, the lens-to-retina distance remains fastened, so the image distance is usually similar for all objects in the least distances. By adjusting the ability of their lenses our eyes manage to try and do this. The procedure of adjustment is acknowledged as accommodation and by varying the form of the lens of our eyes it’s completed.

To form a clear image of an associate entity, the nearest point that it’s placed is called the close to the point of the attention. For an associate object to be lensvisible from the way distance the farthest point at that it must be placed and therefore the point is termed because of the far point of the eye. For the conventional human eye, the variance of vision is between infinity and 25 cm. this can be the space between the way and close to the point of the human eye.

Defects in Eyes

Defect in Eye



Presbyopia Solidification of lens fluid To correct this defect, someone is prescribed a central lens that has each style of lens convex and concave.
Cataract Protein structures of lens clubbed together Cataract surgery involves removing the clouded lens and substituting it with a transparent artificial lens. The unreal lens, known as the associate in the nursing lens, is positioned within the same place as your natural lens. It remains a permanent part of your eye.
Glaucoma Abnormal pressure inside the eye Glaucoma is treated by lowering your eye pressure (intraocular pressure). Betting on your state of affairs, your choices could embody prescription eye drops, oral medications, optical device treatment, surgery, or a mix of any of those.
Myopia Due to a strong refractive index of the eye Shortsightedness is corrected by employing a biconcave (curved inwards) lens that is placed ahead of a myopic eye, moving the image back to the tissue layer and creating it clearer. Hyperopia is corrected by employing a convex (outward facing) lens.
Hyperopia Due to a weak refractive index of the eye Hyperopia will simply be corrected by sporting glasses with connection lenses or contact lenses. Notwithstanding that the degree of ametropia is tiny, correction remains recommended to forestall secondary issues like headaches or eye irritation
Astigmatism Non-uniform curvature of the cornea Astigmatism correction nowadays relies on the employment of special toric contact lenses. Astigmatism can even be corrected by reshaping the membrane through LASIK (laser in place keratomileusis) or PRK (photorefractive keratectomy). PRK removes tissue from the superficial and inner layers of the membrane. LASIK removes tissue solely from the inner layer of the membrane.

Visual defects:

  • Visual defects embrace the shortcoming to ascertain close to objects, or the shortcoming to ascertain so many objects.
  • In recent individuals the lens becomes cloudy, a condition referred to as cataract that impairs vision.
  • Through the eyes normally a person can see distant and nearby objects.
  • At a distance of 25cm, a person with normal eyes can read most comfortably. However, this distance can decrease with age.
  • Also, sometimes people can see far objects clearly but not the nearby objects (farsightedness or hypermetropia).
  • Similarly, some people can see nearby objects clearly but not far objects (nearsightedness or myopia).
  • Sometimes, the lens of the eye can become cloudy or foggy with old age. This condition is called a cataract with results in loss of vision.
  • However, by removing the old lens from the eye and inserting an artificial lens at that place this defect can be rectified.

Care of the eyes:

  1. One has to be compelled to prefer an Associate in Nursing everyday eye check-up.
  2. Wear spectacles if the modality is found weak.
  3. Invariably study or watch TV in good light-weight. Excess or low light can end in problems. Low light can cause strain and winds up in a very severe headache.
  4. Do not examine the sharp provider of sunshine a bit like the sun directly. Excess light-weight can injury the eyes.
  5. If mud enters into the eye one should not rub them and rather wash them right away.
  6. Maintain a regular distance whereas reading or observation TV.
  7. Take a diet to form certain that you simply get the right nutrients.

Power of a lens

If a lens contains a shorter focal distance it’s aforementioned to be a lot of power. The power of a lens is outlined because of the reciprocal distance. Lens power is measured in dioptres (D).

Power of a lens (D) = 1/focal length(m)

P= \frac{1}{f}

Converging (convex) lenses have positive focal lengths, in order that they even have positive power values.

Diverging (concave) lenses have negative focal lengths, in order that they even have negative power values.

Power of the correcting convex lens:

The Lens formula, \frac{1}{v} - \frac{1}{u} = \frac{1}{f}      may be won’t calculate the focal distance and therefore, the facility of the myopia correcting lens.

In this case,

Object distance, u = \infty

Image distance, v = Person’s far point Focal length, f =?

Hence, lens formula becomes

\frac{1}{farpoint} - \frac{1}{\infty} = \frac{1}{focallength}

\frac{1}{farpoint} - 0 = \frac{1}{focallength}

In the case of a lens system, the image is created before the lens i.e., on an equivalent aspect of the item.

Focal length = – Far point

Now, power of the required lens (P) = \frac{1}{f(inm)}

Power of the correcting convex lens:

Lens formula \frac{1}{v} - \frac{1}{u} = \frac{1}{f}      can be accustomed to calculate focal distance f and therefore, power P of the correcting convex lens, where,

Object distance, u = -25 cm, normal near point

Image distance, v = defective near point

Hence, the lens formula is reduced to

\frac{1}{v} + \frac{1}{25} = \frac{1}{f}

What is Night Blindness?

Night blindness conjointly referred to as visual disorder could be a defect within the vision within which individuals cannot read things properly in dim lightweight or at midnight. It mainly happens because of the lack of vitamin A in our body. Thus, always take foods that area unit made in vitamin A like broccoli, inexperienced vegetables, carrot, milk, eggs, curd, papaya, mango, etc.

How will visually impaired individuals browse and write?

  • Visual impairment is additionally called vision loss.
  • A person with vision loss cannot see in the least.
  • This loss of vision is up to a degree that can’t be corrected. Treatment usually suggests glasses or lenses.
  • The folks that haven’t had any visual sense in the least develop the opposite senses of listening and touching sharply that permits them to try to do their day-to-day activities.
  • However, sure resources are developed to assist such people

Sans Eyes:

Braille system:

  • Braille could be a system to browse and write for visually impaired individuals.
  • Consists of sixty-three dot patterns or characters.
  • These patterns are unit brocaded in braille sheets which will be recognized on a bit.
  • The dots are raised so as to form it easier to the touch.

Non-Optical Aids:

  • Visual Aids: They’re used to enlarge words making certain applicable intensity of sunshine fall upon the eyes in order that the person will acknowledge the word.
  • Tactual Aids (using the sense of touch): They embody Braille author Slate and Stylus which permit an individual to browse and write.
  • Auditory Aids (using the sense of listening): They embody devices like audio tapes, talking books, etc.
  • Electronic Aids: They embody talking calculators and computers, electric circuit televisions, and audio CDs, which will facilitate near-blind individuals in listening and writing.
  • Optical Aids: Bifocal Lenses, Contact Lenses, Tinted Lenses, Magnifiers: all of them are units to rectify the restrictions of the eyes.
  • Telescopic Aids: They’re used to read the flat solid and sophistication demonstrations.

Sample Questions

Question 1: A person cannot see objects beyond 1.4 m directly with a myopic eye. What type of corrective lens should be used? What would be its power?


To correct, an object at infinity has to be brought as an image to 140 cm.

\therefore \frac{1}{f} = \frac{1}{-140} - \frac{1}{\infty} = \frac{1}{-140}

f = -140 cm

P = \frac{100}{-140} = \frac{-5}{7}D

  = -0.71 D

Question 2: Magnification is 0.25 when the object distance is 20 cm. Find the power of the concave lens.


m = \frac{v}{u}      = 0.25

\frac{v}{20}     = 0.25

v = 5 cm

Now using:

\frac{1}{v} - \frac{1}{u} = \frac{1}{f}

\frac{1}{-5} - \frac{1}{-20} = \frac{1}{f}

f = -10 cm

P = \frac{100}{-10}     D

  = -10D

Question 3: What is its focal length in the Cartesian system, if the numerical value of the power of this lens 20 D?


P = \frac{1}{f}      (in meters)

P = 10D (given)

10 = \frac{1}{f}

f = \frac{1}{20}

f = 0.2 m

Therefore, the focal length of the lens is 0.2 m as the lens is concave in nature.

Question 4: An object of height 14 cm is placed at a distance of 30 cm from a concave lens. Its focal length is 5 cm. Find the position and size of the image.


Object distance, u = +30 cm (real object)

Focal length, f = -5 cm (concave lens)

Using \frac{1}{u} + \frac{1}{v} = \frac{1}{f}     , we have,

\frac{1}{v} = \frac{1}{f} - \frac{1}{u}

                    = - \frac{1}{5} - \frac{1}{30}

                    = - \frac{7}{30}

Therefore, v = -4.3 cm

m = \frac{v}{u}

   = \frac{\frac{30}{7}}{30}

   = \frac{1}{7}

Height of the image, hi = ho x m

                                     = 14 \times \frac{1}{7}

                                     = 2 cm

The image is virtual, at a distance of 4.3 cm from the lens on the same side as the object and has a height of 2 cm.

Question 5: What is the way purpose and close to the purpose of the human eye with traditional vision?


In optics, the way these associated highest purposes at that an object is brought into focus by the attention square measure known as far purpose and close to the purpose of the attention severally. The way purpose of the human eye with traditional vision is eternity. The close to purpose of the human eye with traditional vision is 25cm.

Question 6: Explain the development of dispersion of sunshine.


Dispersion is outlined because the development of cacophonic of white light-weight into completely different colors on passing through a clear medium like prism. Once white light-weight is well-versed a prism, it splits into seven colors. It’s determined that the colors square measure within the following order:

Violet (V), Indigo (I), Blue (B), Green (G), Yellow (Y), Orange (O) and Red (R).

The order of colors is remembered by the signifier VIBGYOR. This colored band is named spectrum of white light-weight.

Question 7: Explain some common eye defects in human.


Some eye diseases are:

(i) Cataract: A cataract could be a vaporisation of the lens within the eye resulting in a decrease in vision. It will have an effect on one or each eyes. Typically it develops slowly. Symptoms could embody pale colors, indistinct vision, halos around light-weight, hassle with bright lights, and hassle seeing at the hours of darkness. this could lead to hassle driving, reading, or recognising faces. Cataracts square measure the reason for half visual impairment and thirty third of vision defect worldwide. Cataract is treated by exchange the opaque lens with a brand new artificial lens.

(ii) Myopia: Near-sightedness or ametropia, is that the commonest refractive error of the attention. ametropia happens once the eyeball is simply too long, relative to the focusing power of the membrane and lens of the attention. This causes light-weight rays to focus at a degree ahead of the tissue layer, instead of directly on its surface. It is corrected exploitation spectacles fabricated from lens.

(iii) Hypermetropia: Hypermetropia or long-sightedness happens once eyeball is simply too short or the membrane or organ doesn’t refract the sunshine enough. This cause formation of the image of a close-by object behind the tissue layer. A hyperopic person could have blurred vision once staring at objects near to them, and clearer vision once staring at objects within the distance. By inserting a convexo-convex (plus powered) lens ahead of a hyperopic eye, the image is affected forward and focuses properly on the tissue layer.

(iv)Astigmatism: it’s a defect within the eye or during a lens caused by a deviation from spherical curvature, which ends up in distorted pictures, as light-weight rays square measure prevented from meeting at a typical focus. It can be corrected by using a convex lens or concave lens or both.

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Last Updated : 17 Oct, 2022
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