In the normal human eye, light rays travel into the eye through the pupil and are focused through the clear lens onto the retina, a layer of light-sensitive cells at the back of the eye.
The lens is made mostly of water and protein. As we age, the lens continues to grow layers on its surface and hardens. Protein in the lens may clump together and become cloudy in some areas, preventing light from passing clearly through the eye. This cloudiness of the lens is what we call a cataract.
If the clouding is mild or only involves a small part of the lens, your vision may be only slightly affected. If there is more clouding and it affects the entire lens, your vision will become severely limited and cataract surgery becomes necessary.
Less common types of cataracts, not related to normal aging, include the following.
Congenital or developmental cataracts
This type of cataract can occur in infants or children. They may be hereditary or they can be associated with some birth defects. Some occur without any obvious cause.
Non-age related cataracts from other disease or medication
These cataracts are caused by other eye diseases or previous eye surgery. Chronic disease, such as diabetes, or excessive use of steroid medications can spur development of this type of cataract.
These cataracts are related directly to an eye injury. Traumatic cataracts may appear immediately following injury, or they can develop several months or even years later.