The correct option is (c).
Explanation
The human eye functions as a natural optical instrument containing a crystalline lens. It possesses the ability to adjust its focal length to focus on objects at varying distances, a process known as accommodation.- Statement 1 is correct: A normal eye can see both distant and nearby objects clearly. This is achieved by the ciliary muscles, which modify the curvature and focal length of the eye lens. When the muscles are relaxed, the lens becomes thin to focus on distant objects; when they contract, the lens becomes thicker to focus on nearby objects.
- Statement 2 is incorrect: The minimum distance at which objects can be seen most distinctly without strain is called the least distance of distinct vision (or the near point). For a normal human eye, this value is generally 25 cm, not 50 cm. Furthermore, this distance is not constant; it tends to increase with age as the ciliary muscles weaken and the lens loses flexibility (a condition known as presbyopia).
- Statement 3 is correct: In old age, the crystalline lens of the eye may become milky or cloudy. This condition is known as a cataract. It obstructs the passage of light to the retina, causing partial or complete loss of vision, which can often be restored through surgery.
Key Takeaway: The power of accommodation allows the eye to focus at different distances. The standard near point for a normal eye is 25 cm. Cataracts involve the clouding of the eye lens, typically occurring in old age.