Defects of Vision MCQs Quiz | Class 10
This quiz is for Class X, Subject Science (Code 086), Unit III: Natural Phenomena, covering essential topics like Myopia, Hypermetropia, and Presbyopia. Test your knowledge on these common defects of vision and their correction methods. After submitting your answers, you can review them and download a detailed PDF of the questions and your responses.
Understanding Defects of Vision
The human eye is a remarkable organ, but like any biological system, it can develop defects that impair vision. These defects, often called refractive errors, prevent light from focusing correctly on the retina, leading to blurred or distorted vision. The most common defects include Myopia, Hypermetropia, and Presbyopia.
1. Myopia (Nearsightedness)
Myopia is a vision defect where a person can see nearby objects clearly but cannot see distant objects distinctly. The image of a distant object is formed in front of the retina, not directly on it.
Causes:
- Excessive curvature of the eye lens: The lens converges light rays too strongly.
- Elongation of the eyeball: The eyeball is too long, so the retina is further from the lens.
Correction:
Myopia is corrected by using a concave lens of appropriate power. A concave lens diverges the incoming light rays before they reach the eye lens, ensuring that the image is formed precisely on the retina.
2. Hypermetropia (Farsightedness)
Hypermetropia is the opposite of myopia. A person with hypermetropia can see distant objects clearly but has difficulty seeing nearby objects distinctly. The image of a nearby object is formed behind the retina.
Causes:
- Focal length of the eye lens is too long: The lens converges light rays too weakly.
- Shortening of the eyeball: The eyeball is too short, so the retina is too close to the lens.
Correction:
Hypermetropia is corrected by using a convex lens of appropriate power. A convex lens converges the incoming light rays, allowing the eye lens to focus them correctly on the retina.
3. Presbyopia
Presbyopia is an age-related vision defect, typically affecting people over 40-50 years. It results in the gradual loss of the eye’s ability to focus on nearby objects.
Causes:
- Weakening of ciliary muscles: With age, the ciliary muscles, which control the shape of the eye lens, become weaker.
- Decreasing flexibility of the eye lens: The eye lens becomes rigid and loses its ability to change its curvature effectively, thus reducing its power of accommodation.
Correction:
Presbyopia is usually corrected by bifocal lenses. The upper part of a bifocal lens is a concave lens (for distant vision, if also myopic), and the lower part is a convex lens (for near vision).
Summary Table of Vision Defects
| Defect | Symptoms | Causes | Correction |
|---|---|---|---|
| Myopia (Nearsightedness) | Distant objects appear blurred. | Elongated eyeball, excessive lens curvature. | Concave lens |
| Hypermetropia (Farsightedness) | Nearby objects appear blurred. | Shortened eyeball, insufficient lens convergence. | Convex lens |
| Presbyopia | Difficulty reading, blurred near vision (age-related). | Weak ciliary muscles, inflexible lens. | Bifocal lenses |
Quick Revision Points
- Myopia: Image in front of retina, use concave lens.
- Hypermetropia: Image behind retina, use convex lens.
- Presbyopia: Loss of accommodation, use bifocal lenses.
- Power of lens is measured in Dioptres (D).
- Concave lens has negative power; Convex lens has positive power.
Practice Questions (Without options or answers)
- Explain why a person with myopia cannot see distant objects clearly.
- Describe the role of the ciliary muscles in the human eye’s ability to focus.
- What optical principle is used to correct hypermetropia?
- How does the length of the eyeball affect vision in myopia and hypermetropia?
- Why do older people often need different spectacle powers for reading and for seeing distant objects?
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