Why is the normal eye unable to focus on an object placed within 10 cm from the eye?
For a normal eye, the near point (i.e., the minium focus distance) of the eye lens is 25cm. The curvature of the eye lens becomes the maximum (and hence, the focal length becomes the minimum) when an object is placed exactly 25 cm from the eye lens. If an object is placed at a distance of 10 cm (i.e., within the 25 cm distance from the eye lens), then the curvature of the eye lens cannot increase further. Therefore, the focal length of the eye lens does not get adjusted to focus the light rays coming from the object onto the retina. As a result, a blurry image of the object is formed on the retina.