How do the lens expand and contract itself when we see far or near object?

This is all because of the ciliary muscle. This is the type of muscle that you can find in the middle of your eye. This will allow people to view different objects in a more precise manner. Like mentioned, it will be in charge of helping the eyes adjust with the current distance of the items that are seen.

This muscle can either tense or relax in order to make focusing easier for people. The ciliary muscle is also in charge of controlling the amount of light that can enter the eye. It can make the proper adjustments to provide the comfort that they eyes need.