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

Who can see nearer objects clearly ?

A person suffering from defective vision can see objects clearly only beyond 100 cm from the eye. Find the power of lens required so that he can see clearly the object placed at a distance of distinct vision (D = 25cm)

(A) A normal human eye can cleary see all the objects at the different distance. ( R) The human eye has the capacity to suitably adjust the focal length of its lens to a certain extent.

If focal length of the concave mirror is 20 cm, we get virtual image if the object placed at a distance……..than 20 cm

Are we able to see all objects in front of our eye clearly?

Uma cannot able to see the nearer objects clearly, but can see the far objects which lens is very useful to correct his vision defect ?

Kavya can see distant objects clearly but cannot see objects at near distance. With what eye defect is she suffering ? Draw the diagrams showing the defected eye and its correction ?