Question

When you look at an object very close to your eyes, the:

• A. Ciliary muscles of your eye contract and the eye lens becomes thick.
• B. Ciliary muscles of your eye get relaxed and the eye lens becomes thick.
• C. Ciliary muscles of your eye contract and the eye lens becomes thin.
• D. Ciliary muscles of your eye get relaxed and the eye lens becomes thin.

Hint:

Accommodation:

• \textbf{Near object:} Ciliary muscles contract \(\Rightarrow\) Lens thick \(\Rightarrow\) Focal length decreases
• \textbf{Distant object:} Ciliary muscles relax \(\Rightarrow\) Lens thin \(\Rightarrow\) Focal length increases

This ability decreases with age (presbyopia).

Answer 1

The Correct Option is A

Step 1: Understand the process of accommodation in human eye.
The human eye has the ability to adjust its focal length to see objects at different distances clearly. This ability is called accommodation.
Step 2: Role of ciliary muscles and eye lens.

• The eye lens is a flexible, transparent structure whose curvature can be changed.
• The ciliary muscles are attached to the lens by suspensory ligaments.
• When the ciliary muscles contract or relax, they change the tension on the lens, altering its shape and focal length.

Step 3: Mechanism for viewing nearby objects.
When looking at objects very close to the eye:

• The ciliary muscles contract.
• This reduces the tension on the suspensory ligaments.
• The lens becomes more rounded or thick (increased curvature).
• Increased curvature decreases the focal length, allowing the eye to focus the diverging rays from nearby objects onto the retina.

Step 4: Mechanism for viewing distant objects.
For comparison, when looking at distant objects:

• The ciliary muscles relax.
• This increases tension on the suspensory ligaments.
• The lens becomes thin (flattened, decreased curvature).
• Decreased curvature increases focal length for parallel rays from distant objects.

Step 5: Analysis of options.

• (A) Ciliary muscles contract and lens becomes thick: Correct. This is exactly what happens for near vision.
• (B) Ciliary muscles relax and lens becomes thick: Incorrect. Relaxation makes lens thin.
• (C) Ciliary muscles contract and lens becomes thin: Incorrect. Contraction makes lens thick.
• (D) Ciliary muscles relax and lens becomes thin: Incorrect. This happens for distant vision, not near vision.

Final Answer: (A) Ciliary muscles of your eye contract and the eye lens becomes thick.