Cataract is a clouding of the eye's lens. When we look at something, light rays travel into our eye through the pupil and are focused through the lens onto the retina, a layer of light-sensitive cells at the back of the eye. The lens must be clear in order to focus light properly onto the retina. If the lens has become cloudy, this is called a cataract.
As a cataract slowly begins to develop, you may not notice any changes in your vision at first. But as the cataract progresses, you may begin to find that it interferes with your daily activities. Performing a complete eye exam, your ophthalmologist (Eye M.D.) can tell you whether cataract or another problem is the cause of your vision loss.