defect of vision and their correction pdf

Defect of vision and their correction pdf

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Human Eye and Colourful World

Human Eye: working of human eye, Persistence of vision, Power of accommodation of human eye, Defects of vision. The Human Eye: It is a natural optical instrument which is used to see the objects by human beings.

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Question 1 What is myopia? State the two causes of myopia? Question 5 What are the two common defects of vision? Question 6 What type of spectacles should be worn by a person having the defects of myopia and hypermetropia? Question 7 What is presbyopia? Write two causes of this defects? Question 8 What is cataract? How is the vision of a person having cataract restored? Question 9 What are the advantages of having two eyes instead of just one?

Question 10 What precautions should be taken while donating eyes? The ability to see is called vision. It is also called eyesight. There are three common defects of vision or defects of eye. These lenses are usually used in the form of eye- glasses or spectacles. The defect of eye called myopia or short-sightedness is caused. The far point of eye having myopia or short-sightedness is at point F which is less than infinity. The parallel rays of light coming from the distant object O at infinity are converged to form an image I in front of the retina due to which the eye cannot see the distant objects clearly.

The image is formed in front of the retina either due to high converging power of eye-lens or due to eye-ball being too long. The far point of eye having myopia is at point F which is less than infinity.

If the distant object can be made to appear as if it were at the far point F of this eye, then the eye can see it clearly. This is done by putting a concave lens in front of the eye. Myopia is corrected by using spectacles containing concave lenses. When a concave lens L of suitable power is placed in front of the myopic eye. Then the parallel rays of light coming from the distant object are first diverged by the concave lens. The focal length of concave lens needed to correct myopia or short-sightedness in a person is calculated by using the lens formula:.

The defect of eye called hypermetropia or long- sightedness is caused. The image is formed behind the retina either due to low converging power of eye- lens or because of eye-ball being too short. Because of this an old person cannot see the nearby objects clearly. Cataract decreases the vision of the eye gradually. Advantages of having two eyes are:.

All the predators like tiger, lion, etc. Some of the important points to be noted about the donation of eyes are the following:. University and has many years of experience in teaching. Thanks , it really of great help. I found it simpler to understand. My pre medical physics will has really be so easier now in relation to the eyes defects and correction. I will be grateful if you help me on the function and structure of the eye. Thanks a lot for you educational support through this website.

By reading with comprehensive method I was strong enough to do my assignment. Ah this is really great. God will continue to bless and strengthen you. Your email address will not be published. Contents 1 Defects of vision and their correction 2 Myopia Short-sightedness or Near-sightedness 3 1 Due to high converging power of eye-lens because of its short focal length 4 2 Due to eye-ball being too long 5 Myopia short-sightedness or near-sightedness is corrected by using spectacles containing concave lenses.

Comments Tq so much it is very useful and also easy to under stand. It has been of help to me. Leave a Reply Cancel reply Your email address will not be published.

Defects of vision and their correction pdf creator

Below are given the nature of the defect, its causes and corrective measures Nearsightedness , also called myopia is a common name for impaired vision in which a person sees near objects clearly while distant objects appear blurred. In such a defective eye, the image of a distant object is formed in front of the retina and not at the retina itself. Consequently, a nearsighted person cannot focus clearly on an object farther away than the far point for the defective eye. This may arise due to either. This defect can be corrected by using a concave diverging lens.


There are mainly three common refractive defects of vision. These are. (i) myopia or near-sightedness. (ii) Hypermetropia or far – sightedness. (iii) Presbyopia.


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It is an optical instrument just like a photographic camera. It forms the real image of the object on retina of the eye. For normal eye, the range of vision is from 25 cm to infinity. Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea.

The day aims to focus attention worldwide on blindness and vision impairment. The Human eye works on the refraction of light through a natural convex lens made up of transparent living material and enables us to see things around us. And the ability to see is called vision, eyesight, or drishti. The human eye consists of the cornea, iris, pupil, ciliary muscles, eye lens, retina, and optical nerve.

The Human Eye: Anatomy, Structure, Working, Function and Defects

Refractive error , also known as refraction error , is a problem with focusing light accurately on the retina due to the shape of the eye. Near-sightedness is due to the length of the eyeball being too long, far-sightedness the eyeball too short, astigmatism the cornea being the wrong shape, and presbyopia aging of the lens of the eye such that it cannot change shape sufficiently.

Human Eye and Colourful World

JavaScript seems to be disabled in your browser. You must have JavaScript enabled in your browser to utilize the functionality of this website. Myopia occurs when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface If you're nearsighted, the first number "sphere" on your eyeglasses prescription will be preceded by a minus sign —. The higher the number, the more nearsighted you are.

There are many eye related problems and defects of the eye, the main few are briefly discussed below:. Defects of the eye:. Myopia: nearsightedness This is a defect of vision in which far objects appear blurred but near objects are seen clearly. Hyperopia: farsightedness This is a defect of vision in which there is difficulty with near vision but far objects can be seen easily.

Question 1 What is myopia?

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