Chapter 10 · Question 2
Explain the term 'power of accommodation' of the human eye and describe how it helps us see objects at different distances.
Q2
Explain the term 'power of accommodation' of the human eye and describe how it helps us see objects at different distances.
Answer Revealed
Direct Answer:
Power of accommodation is the ability of the eye lens to adjust its focal length with the help of ciliary muscles, allowing us to see objects clearly at varying distances.
Simple Explanation
Your eye lens can change shape to focus on things near or far — like a camera autofocus. Ciliary muscles squeeze the lens to make it thicker for nearby objects and flatten it for distant ones. This flexibility is called accommodation.
Exam-Ready Structure
The power of accommodation is the ability of the eye lens to change its focal length so that objects at different distances can be focused clearly on the retina. The mechanism works as follows: 1. The ciliary muscles attached to the eye lens can contract or relax. 2. When viewing a nearby object, the ciliary muscles contract, making the lens thicker and shorter in focal length, allowing the converging rays from a near object to focus on the retina. 3. When viewing a distant object, the ciliary muscles relax, the lens becomes thinner and longer in focal length, allowing the nearly parallel rays from a far object to focus on the retina. 4. The near point (least distance of distinct vision) for a normal young adult eye is about 25 cm. 5. The far point for a normal eye is infinity. 6. This continuous adjustment happens automatically and allows us to switch focus between objects at different distances almost instantly.
Key Points
- Adjustment of eye lens focal length by ciliary muscles
- Lens becomes thicker (shorter focal length) for near objects
- Lens becomes thinner (longer focal length) for distant objects
- Near point of normal eye: about 25 cm
- Far point of normal eye: infinity