Basic Facts

What are Cataracts?

The lens of the eye is a clear structure that lies behind the iris and the pupil. Normally, light passes through it easily. The lens then focuses the light so that it falls onto the retina at the back of the eye. This allows us to see things clearly both up close and far away.  This process is blocked if we develop a cataract, which is a clouding and darkening of the lens. 

The lens of the eye is made mostly of water and protein that keep the lens clear and allow light to pass through. As long as the lens is clear—as it is when we are young and healthy—the retina receives a sharp image. But as we age, cataracts can develop, and the image gets blurry, dull, or indistinct. It can feel like looking through a thick mist or a foggy window. However, cataracts are not involved in the general loss of visual sharpness (acuity) that all of us experience as we age. 

Cataracts can occur in one eye or in both, but they never spread from one eye to the other.

In the beginning, cataracts are small and don’t block very much light. At this stage, you don’t notice any changes. Unfortunately, cataracts grow. Slowly, as cataracts grow larger and start to block more and more light, your vision worsens. Eventually, you may have trouble reading, driving, telling different colors apart, and carrying out your regular activities. These problems are often worse at night.  

Stronger lighting and eyeglass adjustments can help when cataracts are small. As cataracts grow, many people need surgery. 

How Common Are Cataracts?

Cataracts are a common result of aging and occur frequently in older people. About one in five adults over the age of 65 has a cataract. If you are in your mid-seventies to eighties, you have a 50% chance of developing one. Approximately 1.5 million cataract operations are performed every year in the US. 

The Most Common Types of Cataracts

Cataracts are categorized depending on their location. They may be:

  • Nuclear Cataracts appear in the center of the lens. They may cause double vision or even multiple copies of an image.
  • Cortical Cataracts affect the edges of the lens, and causes problems with glare.
  • Posterior Subcapsular Cataracts occur on the back of the lens. They reduce your ability to read, even in bright light, and may cause glare or halos around lights at night. 

Aging is the most common cause of cataracts. Other kinds of cataracts are grouped according to their causes. They are known as:

  • Secondary cataracts sometimes form because of a chronic illness such as diabetes, after surgery for other eye problems, or from long-term steroid use.
  • Traumatic cataracts result from an eye injury.
  • Congenital cataracts appear in newborn babies or in childhood. They may be caused by a genetic mutation or as a result of an illness in the mother during pregnancy.
  • Radiation cataracts may occur after severe exposure to ionizing radiation.

Last Updated July 2020