The focal length of the eye lens is changed by the action of the ciliary muscles.
These muscles control the shape of the lens, which in turn alters its focal length, allowing us to focus on objects at varying distances. This process is called accommodation.
Here's a breakdown:
- Ciliary Muscles and Lens Shape: The ciliary muscles are a ring of muscle tissue located around the lens of the eye.
- Focusing on Distant Objects: When viewing distant objects, the ciliary muscles relax. This causes the suspensory ligaments (fibers connecting the ciliary muscles to the lens) to tighten, which pulls the lens into a flatter, thinner shape. The flatter lens has a longer focal length, enabling the eye to focus on faraway objects.
- Focusing on Near Objects: When viewing close objects, the ciliary muscles contract. This slackens the suspensory ligaments, allowing the lens to become more rounded and thicker due to its own elasticity. The rounded lens has a shorter focal length, enabling the eye to focus on nearby objects.
In summary, the ciliary muscles control the tension on the suspensory ligaments, which in turn affects the shape, and thus the focal length, of the eye lens. This dynamic adjustment allows the eye to focus on objects at different distances.
