Purpose

• When humans see, it is because their eyes are processing the light reflecting off of objects. The purpose of the lens is to focus these light rays entering the eye. The lens is responsible for approximately 20 percent of the optical power of the eye, according to the Georgia State University's website on eye anatomy.
  
  

Size

• The Georgia State University eye anatomy site reports that the lens is about 9 mm in diameter and 4 mm thick. The lens is flexible and changes shape depending on how far an object is. When the eye focuses on a far away object, the lens becomes thinner. It becomes more rounded and thicker when focusing on closer objects.
  
  

Conditions

• Misshapen or damaged lens can cause vision problems. The lens, which is normally clear, sometimes becomes darkened or cloudy. This is known as a cataract, which can be removed by surgical procedure. Normal lens are shaped like spheres; humans with lens more cylinder-shaped can have an astigmatism. Astigmatisms cause vision impairment because there is no specific focus point for the eye.