Long-sightedness is caused due to

Options

A. eye ball being too short.
B. eye ball being too long.
C. the blind spot on the retina.
D. None of the above.

Explanation

**Step-by-Step Solution:**

1. **Understanding Long-Sightedness**: Long-sightedness, also known as hypermetropia, is a condition where a person can see distant objects clearly but has difficulty focusing on nearby objects.

2. **Analyzing the Eye Structure**: In a normal eye, light rays from an object should converge on the retina to form a clear image. The eye consists of the eyeball, lens, and ciliary muscles that help in focusing.

3. **Identifying the Problem**: In long-sightedness, the image of nearby objects is formed behind the retina instead of directly on it. This results in a blurry image for close objects.

4. **Considering the Options**:
- **Option 1: Eyeball being too short**: This is the correct option. If the eyeball is shorter than normal, the light rays converge behind the retina, leading to difficulty in seeing close objects.
- **Option 2: Eyeball being too long**: This would cause the image to form in front of the retina, which is not the case for long-sightedness.
- **Option 3: Blind spot on the retina**: A blind spot would not allow any image to form, which is not the reason for long-sightedness.
- **Option 4: None of these**: This option is incorrect since we have identified a valid cause.

5. **Conclusion**: The cause of long-sightedness (hypermetropia) is primarily due to the eyeball being too short, which causes the image of nearby objects to form behind the retina.

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