What is the power of accommodation? How do the ciliary muscles achieve this ?
 

The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called the accommodation of the eye.

Power of Accommodation

The ability of the eye to focus objects lying at different distances is called the power of accommodation of the eye.

How Does an Eye Focus Objects at Varying Distances?
To focus on distant objects the ciliary muscles relax making the eye lens thin.
As a result the focal length of the eye lens increases and we see the distant objects.
But to focus on nearby objects the ciliary muscles contract making the eye lens thick. As a result the focal length of the eye lens decreases and we see the nearby objects.
In short it is the adjustment of the focal length of the eye lens which enables us to focus on objects situated at different distances.

Near point or Least Distance of Distinct Vision

Near point or least distance of distinct vision is the point nearest to the eye at which an object is visible distinctly.
For a normal eye the least distance of distinct vision is about 25 centimetres.
However, it varies with age of the person. For example, for infants it is only 5 to 8 cm.

Far Point
Far point of the eye is the maximum distance up to which the normal eye can see things clearly. It is infinity for a normal eye.

Range of Vision

The distance between the near point and the far point is called the range of vision.