write the defect of vision
Answers
Answer:
In such conditions, the person cannot see the objects distinctly and comfortably. The vision becomes blurred due to the refractive defects of the eye. There are mainly three common refractive defects of vision. These are (i) myopia or near-sightedness, (ii) Hypermetropia or far – sightedness, and (iii) Presbyopia.
Answer:
Defects of vision is the loss of power of accommodation of the human eye. They are mainly of three types:
Myopia/ near-sightedness: The person can see nearby objects clearly but is unable to see objects beyond some distance. For such a person, far point changes to infinity to some finite distance. It is corrected with the help of a concave lens. The power of the lens is set so that its focal length is equal to the far-point of the eye.
Hypermetropia/ far-sightedness: The person can see far objects clearly but is unable to see nearby objects clearly. For such a person, near point increases to a distance greater than 25 cm. It is corrected with the help of a convex lens. The power of the lens is set so that the image of an object kept at 25 cm from the lens is formed at near-point of the eye.
Presbyopia: This defect is common in old-people and is caused by the weakening of ciliary muscles. In this defect, both the near-point and the far-point are affected. It is corrected with the help of a bifocal length which is a combination of convex lens and a concave lens.
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