Explanation

(a) Our eye lens has a power to adjust its focal length to see the nearer and father objects, this process of adjusting focal length is called accommodation. However, if the object is brought too close or bring too far from the eye, the focal length cannot be adjusted to from the image on the retina. Thus, there is minimum or maximum distance for the clever vision of an object. For a normal eye, near point or least distant vision $D$ = 25 cm and far point = $\infty$