Final answer:
The ciliary muscles control the shape of the lens in the eye, allowing it to adjust and focus light on the retina for clear vision at various distances, a process called accommodation. The lens becomes more convex for close vision and less convex for distant vision.
Step-by-step explanation:
The shape of the lens is controlled by the ciliary muscles. These muscles adjust the lens's shape to focus light properly onto the retina, allowing us to see objects at various distances clearly. This process is known as accommodation. When the lens changes shape to become more convex (thicker), it increases its focusing power, which is essential for viewing objects that are close. On the other hand, for objects far away, the ciliary muscles relax, allowing the lens to become less convex (thinner) and thereby decreasing its focusing power. This fine-tuning of the lens ensures that light rays from both distant and nearby objects can be focused sharply on the retina.
The ability of the eye to accommodate decreases with age, and some people may require corrective lenses to help them focus on nearer objects, such as reading material or a computer screen. This age-related decline in the ability to change the lens shape is mostly due to the loss of elasticity in the lens itself and a weakening of the ciliary muscles.