A cataract is a clouding of the lens in the eye that affects vision. Cataracts are common in older people. A cataract can occur in either or both eyes. It cannot spread from one eye to the other.
As we age, some of the proteins in our eyes may clump together and start to cloud a small area of the lens. This is a cataract. Over time, the cataract can grow larger and cloud more of the lens, making it harder to see.
Researchers suspect that there are several causes of cataract, such as smoking and diabetes. Or, it may be that the protein in the lens just changes clumps from the wear and tear it takes over the years.