The Human Eye

Myopia is a condition where a person can see nearby objects clearly but cannot see distant objects clearly. Hence, it is also known as near sightedness. Hypermetropia is a condition where a person can see distant objects clearly but has difficulty in seeing nearby objects. Hence, it is also called far sightedness.

The correct option is (C): Both (a) and (b) are true

The retina contains photoreceptor cells (rods and cones) that detect light and convert it into electrical signals. These signals are then transmitted to the brain for processing. The structure responsible for carrying these signals from the retina to the brain is the optic nerve. The optic nerve is a bundle of nerve fibers that exits the eye at the optic disc and connects to the visual cortex in the brain, enabling the perception of vision.

Other options can be ruled out as follows:

• Ciliary muscle: This controls the shape of the lens to help focus light onto the retina but does not transmit visual signals.
• Cornea: This is the transparent outer layer of the eye that helps refract light but does not carry signals to the brain.
• Iris: This regulates the amount of light entering the eye by adjusting the pupil size and is not involved in signal transmission.

Final Answer: The correct answer is , which corresponds to option .

The maximum focal length of the eye-lens for a person with myopia is less than 2.5 cm because myopia causes the far point of the eye to shift closer, reducing the lens's ability to focus on distant objects.

Final Answer: The maximum focal length of the eye-lens is , which corresponds to option .

The defect described here is myopia (nearsightedness), where a person cannot see objects placed beyond a certain distance (the far point) clearly, and typically objects placed between the near point and the point of least distance of distinct vision appear blurry.

Correction:

The defect of myopia can be corrected using a concave lens (also called a diverging lens). This lens helps diverge the light rays before they enter the eye, shifting the focal point to the retina.

Correct Answer:

The defect can be corrected by using a bi-concave lens.

So, the correct option is:

bi-concave lens

Correct answer: 2.5 to 25 cm

Explanation:
The accommodation of the eye lens refers to its ability to adjust its focal length to focus on objects at different distances.

For a healthy human eye: - The least distance of distinct vision is about 25 cm. - The eye can normally focus on objects as close as 25 cm and as far as infinity. - The accommodation range (in terms of focal length change) corresponds roughly to the range of 2.5 cm to 25 cm when considering how the eye adjusts focus for near and far objects.

Hence, the correct answer is: 2.5 to 25 cm.

Correct answer: myopia

Explanation:
Myopia, also known as nearsightedness, is a vision defect where a person cannot see distant objects clearly, but can see nearby objects without difficulty.

This happens because the image of a distant object is formed in front of the retina instead of on it. It is usually caused by: - An elongated eyeball, or - A too curved eye lens.

Correction: Myopia is corrected using a concave lens, which diverges light rays before they enter the eye.

Other options:
- Hypermetropia: Farsightedness – difficulty seeing nearby objects.
- Presbyopia: Age-related condition affecting both near and far vision.
- Angle of vision: Not a defect of vision.

Hence, the correct answer is: myopia.

Correct answer: vision

Explanation:
The human eye functions based on the principle of the sensation of vision, which involves the detection of light and its conversion into electrical signals by the retina. These signals are then interpreted by the brain to form images.

The eye is sensitive to visible light, and vision is made possible due to the focusing of light rays onto the retina through the cornea and lens.

Hence, the correct answer is: vision.

The ciliary muscles are responsible for adjusting the focal length of the eye lens. When the ciliary muscles contract, they change the shape of the lens, making it thicker for near vision and thinner for distant vision. This process is known as accommodation. Thus, the ciliary muscle helps the eye lens to change its focal length.

The correct option is (B): ciliary muscle

Step 1: Understand the cause of myopia.
Myopia (nearsightedness) occurs when the image of distant objects is formed in front of the retina.
Step 2: Determine the type of lens needed for correction.
A concave lens diverges the incoming light rays, causing the image to be formed farther back on the retina, thus correcting myopia.
Step 3: Recall the function of other lenses.
Convex lens: Converges light rays (used for hypermetropia).
Bifocal lens: Has both converging and diverging sections (used for presbyopia).
Plano-convex lens: A type of converging lens.