Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

A normal eye sees objects with the help of converging eye lens. The ciliary muscles contact and expand thereby changing the converging power of the lens. The near point of our eyes is 25 cm i.e. our eyes can see clearly with minimum distance of 25 cm. But, when the distance between the object and our eyes is less than 25 cm, the ciliary muscles are unable to focus sharply. Thus, we cannot see with naked eye and need the support of any external device to see the object with distance less than 25 cm