Final answer:
When an object is close, the eye's lens becomes more rounded to increase its converging power for clear vision. The alteration is due to the ciliary muscles making the lens thicker, which is necessary for close-up focus on objects.
Step-by-step explanation:
When viewing an object that is close, the lens in your eye should be more rounded. This is because light rays from a nearby object diverge, and the lens has to be more converging to focus these rays onto the retina, allowing for a clear image.
This adjustment in lens shape is achieved by the contraction of the ciliary muscles, which makes the lens thicker and more convex, enhancing its ability to refract light. This state of eyesight is often termed as accommodated, in contrast to the relaxed state of the eye when viewing distant objects.
Prescription eyeglasses with convex lenses can assist those with presbyopia—a condition where the lens of the eye is unable to focus properly on close objects—by compensating for the reduced ability to change the lens curvature.