This precise focusing of incoming light is how clear vision is achieved.
In patients under 50 years of age, the lens is able to change shape and alter the focus of incoming light. Beyond this age, the ability to change shape is lost.
Cataract is a condition where the lens loses its clarity and becomes cloudy. As a consequence incoming light is scattered, impairing focus of the light, and vision becomes blurred. Surgery involves cataract removal of the cloudy lens and replacement with an artificial lens.