¶¶ the change in focal length of an eye lens is caused by the action of ciliary muscles.

¶¶ Hence option A is correct.

The correct answer is option 'A', the change in the focal length of an eye lens is caused by the action of the ciliary muscles.

The eye lens is a flexible and transparent structure located behind the iris. It plays a crucial role in focusing light onto the retina, which is responsible for forming clear images. The focal length of the lens determines the point at which the light converges, and it can be adjusted to focus on objects at varying distances.

The ciliary muscles are a ring of smooth muscles that surround the lens. They are attached to the lens by a series of fibers called suspensory ligaments. When the ciliary muscles contract or relax, they cause changes in the shape and curvature of the lens, leading to a change in its focal length.

Explanation of how the ciliary muscles work:
1. Contracted ciliary muscles: When the eye is focusing on a nearby object, the ciliary muscles contract. This action releases tension on the suspensory ligaments, allowing the lens to become more rounded and thicker. As a result, the focal length of the lens decreases, allowing it to focus the light rays from the nearby object onto the retina.

2. Relaxed ciliary muscles: Conversely, when the eye is focusing on a distant object, the ciliary muscles relax. This relaxation creates tension on the suspensory ligaments, causing the lens to become flatter and thinner. This change in shape increases the focal length of the lens, allowing it to focus the light rays from the distant object onto the retina.

Importance of ciliary muscles in maintaining clear vision:
The ability of the ciliary muscles to adjust the focal length of the lens is crucial for maintaining clear vision at different distances. Without the action of the ciliary muscles, the lens would remain in a fixed position, making it difficult to focus on objects at varying distances. This ability to accommodate for different distances is known as accommodation, and it is an essential function of the eye for clear vision.

In summary, the ciliary muscles play a vital role in adjusting the focal length of the eye lens. By contracting or relaxing, these muscles change the shape and curvature of the lens, allowing it to focus on objects at different distances. Without the action of the ciliary muscles, the eye would not be able to accommodate for different distances and maintain clear vision.