A cataract is a clouding of the lens of the eye. This is an area that is normally clear. As this clouding happens, it keeps light rays from passing through the lens and focusing on the retina. The retina is a tissue lining that is sensitive to light. It is located in the back of the eye. This cloudiness happens when some of the protein which makes up the lens of the eye begins to change its structure. It then gets in the way of your eyesight.