A cataract is a clouding of the eye’s natural lens, which lies behind the iris and the pupil. Most cataracts are related to aging but can also occur due to injury or disease. For people who have cataracts, seeing through cloudy lenses is a bit like looking through a frosty or fogged-up window. Cataracts are very common in older people. By age 80, more than half of the population either have a cataract or have had cataract surgery. A cataract can occur in either or both eyes. It cannot spread from one eye to the other. If the cataract develops to the point that it affects your daily activities, surgery may be recommended.