Question

Why is a normal eye not able to see clearly the objects placed closer than $25\mathrm{cm}$?

Answer 1

Human eye:

1. In a normal eye, ciliary muscles flex and expand in order to modify the focal length of the eye lens, allowing it to see objects at different distances.
2. When objects are closer than the point of $25\mathrm{cm}$, too much contraction puts a lot of strain on the eye muscles, and the eye is unable to concentrate its image on the retina.

Therefore, a typical eye cannot easily see objects closer than $25\mathrm{cm}$.