Final answer:
The adjustment of the lens for clear vision at different distances, known as c) accommodation, involves changing the lens curvature to adjust its optical power, helping to focus light precisely on the retina.
Step-by-step explanation:
The adjustment of the lens so that you can see objects both near and far is called accommodation. This process allows the eye to change its focal length to focus on objects at different distances effectively. The lens of the eye achieves this by varying its curvature, becoming more curved for close objects to increase its optical power and flatter for distant objects to decrease its optical power. Myopia (nearsightedness) and hyperopia (farsightedness) are visual conditions that are corrected using lenses that adjust the optical power of the eye, helping to form clear images at various distances. Nearsightedness is addressed with a diverging lens, while farsightedness is corrected with a converging lens. For clear vision, the image must be focused directly on the retina, which is achieved through the process of accommodation. Figure 26.4 demonstrates that when we look at distant objects, the light rays entering the eye are almost parallel and require less refraction to focus on the retina, requiring the lens to be less powerful and more relaxed. In contrast, light from close objects diverges more and necessitates a more powerful, thicker lens to focus the light on the retina, showing the eye in a fully accommodated state.