Like the lens of a camera, the eye's lens focuses to keep the images of both close and distant objects clear. Over time, the lens becomes less transparent; studies suggest accumulated exposure to ultraviolet light causes the natural lens to cloud. Most often, this clouding takes place slowly as proteins within the lens degenerate.
Cataracts do NOT generally cause pain, discomfort, redness, discharge, or sudden, alarming vision changes that would lead you to seek immediate help. The changes caused by cataracts generally develop so slowly that you don't notice them until they are serious enough to affect normal lifestyles.
Note: Even if you think you do not have cataracts, you should seek medical attention if you are having troublesome eye symptoms.