Corrections of Vision MCQs Quiz | Class 10

This quiz on Class X Science (Code 086), Unit III: Natural Phenomena, focuses on ‘Corrections of Vision MCQs Quiz | Class 10’. It covers essential concepts related to corrective lenses and their various applications. Test your understanding, then submit to see your score and download a detailed answer PDF.

Understanding Corrections of Vision

Our eyes are remarkable organs, but like any intricate system, they can sometimes develop defects that hinder clear vision. These refractive defects occur when the eye fails to focus light precisely on the retina. Fortunately, most common vision defects can be corrected using appropriate corrective lenses, which are specific types of spectacles or contact lenses.

Common Vision Defects and Their Corrections:

There are three primary refractive defects of vision:

  1. Myopia (Near-sightedness): A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.
  2. Hypermetropia (Far-sightedness): A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.
  3. Presbyopia: This defect arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens with age, making it difficult to see nearby objects comfortably and clearly.

Corrective Lenses and Their Applications:

The type of corrective lens used depends on the specific defect:

  • Myopia Correction:

    Myopia is caused because the eye lens converges light rays too strongly, or the eyeball is too long. The image of a distant object is formed in front of the retina. This defect can be corrected by using a concave lens of appropriate power. A concave lens diverges the incoming light rays sufficiently so that the image is formed on the retina.

  • Hypermetropia Correction:

    Hypermetropia is caused because the eye lens converges light rays too weakly, or the eyeball is too short. The image of a nearby object is formed behind the retina. This defect can be corrected by using a convex lens of appropriate power. A convex lens converges the incoming light rays sufficiently so that the image is formed on the retina.

  • Presbyopia Correction:

    Presbyopia usually requires a convex lens to correct the near vision. Often, people with presbyopia may also have myopia or hypermetropia, necessitating bifocal lenses. Bifocal lenses consist of both concave and convex lenses: the upper portion is a concave lens (for distant vision) and the lower portion is a convex lens (for near vision).

  • Astigmatism:

    This is another common refractive error where the eye does not focus light evenly on the retina, often due to an irregularly shaped cornea or lens. It causes blurred or distorted vision at all distances. Astigmatism is corrected using cylindrical lenses.

Summary Table of Vision Defects and Corrections:

Vision Defect Cause Correction (Lens Type) Symptoms
Myopia (Nearsightedness) Elongated eyeball or excessive curvature of eye lens Concave lens Clear near vision, blurred distant vision
Hypermetropia (Farsightedness) Shortened eyeball or insufficient curvature of eye lens Convex lens Clear distant vision, blurred near vision
Presbyopia Weakening ciliary muscles, less flexible lens (age-related) Convex lens (bifocal if combined with other defects) Difficulty focusing on near objects
Astigmatism Irregularly shaped cornea or lens Cylindrical lens Blurred or distorted vision at all distances

Quick Revision Points:

  • Myopia means light focuses in front of the retina.
  • Hypermetropia means light focuses behind the retina.
  • Concave lenses diverge light and are used for myopia.
  • Convex lenses converge light and are used for hypermetropia and presbyopia.
  • Power of lens (P) = 1/f (where f is focal length in meters). Unit is Dioptre (D).
  • A negative power indicates a concave lens, and a positive power indicates a convex lens.
  • Bifocal lenses combine concave and convex powers for both distant and near vision.

Additional Practice Questions:

  1. Why is it important for a myopic person to wear glasses with a concave lens?
  2. Describe the symptoms a person with hypermetropia experiences when trying to read a book.
  3. Explain why the power of a corrective lens is measured in Dioptres.
  4. What is the function of the ciliary muscles in the human eye, and how does their weakening contribute to presbyopia?
  5. Differentiate between the focal length of a convex lens used to correct hypermetropia and a concave lens used to correct myopia.