Question

Why cant we see an object when it is placed very close to our eyes?

Answer 1

To see an object comfortably and distinctly, the distance of object should be at least 25 cm from the eyes. Due to this, a normal eye is not able to see clearly the objects placed closer than 25 cm. This distance at which objects can be seen is clearly, is called the least distance of distinct vision or the near point of the eye.
Hence we can't see objects when placed close to our eyes

Answer 2

because if object is very close to eyes than the image is formed not on retina of our eyes....
this is because there is a minimum limit for the adjustment of curvature of our eye lens ... so light rays doesnot refract properly....
the minimum distance for seeing changes as our age increses....