Question

When does the focal distance of eyes increase?

Answer 1

For a skinny lens in air, the focal distance is that the distance from the middle of the lens to the principal foci (or focal points) of the lens. For a convex lens (for example a convex lens), the focal distance is positive and is the distance at which a beam of collimated light is going to be focused to one spot.

Complete step by step solution:
When the muscles are relaxed, the lens becomes thin. Thus, its focal distance increases. it's the ciliary muscles which will modify the curvature of the lens to vary its focal distance . to ascertain a foreign object clearly, the focal distance of the lens should be larger.
The change in curvature of the attention lens changes the focal distance of the eyes. Hence, the change in focal distance of an eye fixed lens is caused by the action of ciliary muscles. For this, the ciliary muscles relax to decrease the curvature and thereby increase the focal distance of the lens.
The eye lens is formed from a fibrous, jelly-like material. Its curvature is often modified to vary its focal distance to some extent by the ciliary muscles. When the muscles are relaxed, the curvature decreases making the lens thin and therefore the focal distance increases.
Note: Once we take a thick lens the sunshine travels an extended path inside the lens compared to a thinner lens. Then when it comes out of the subsequent surface it cuts the principle axis at a shorter distance.