Cataracts: An Overview

What is a cataract?

A cataract is a clouding of the eye’s natural (crystalline) lens. This lens, located behind the iris and the pupil, works a lot like a camera. Light rays focus through your lens onto the retina, a layer of light-sensitive cells at the back of the eye. Similar to photographic film, the retina allows the image to be “seen” by the brain.

Over time, the lens of our eye can become cloudy, preventing light rays from passing clearly through the lens. The loss of transparency may be so mild that vision is barely affected, or it can be so severe that no shapes or movements are seen—only light and dark. When the lens becomes cloudy enough to obstruct vision to any significant degree, it is called a cataract.

What causes a cataract?

Cataracts are often a common part of aging. As the majority of people grow older, their natural lenses begin to cloud over as proteins clump together on the lens. While the exact cause of cataract development is still debated, research points to overexposure to ultraviolet (UV) light, trauma from eye injury, steroids, smoking, and certain diseases such as diabetes as leading causes of cataracts. Very rarely, babies are born with cataracts, known as congenital cataracts.

What are signs and symptoms of a cataract?

Cataracts typically develop slowly and progressively, causing a gradual and painless decrease in vision. Other changes you might experience include blurry vision; glare, particularly at night; frequent changes in your eyeglass prescription; a decrease in color intensity; a yellowing of images; and in rare cases, double vision.