Aging & Health A to Z
Basic Facts & Information
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 in a precise way. This focusing ability of the lens lets us see things clearly both up close and far away. From the retina, the light signals are transmitted along the optic nerve to the brain, where they are interpreted as images. 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 molecules 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.
Cataracts can occur in one eye or in both, but they never spread from one eye to the other.
Cataracts are not involved in the general loss of visual sharpness (acuity) that all of us experience as we age. That comes from changes in the shape of the eye, weaker eye muscles, and smaller pupil size.
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, cataracts block more and more light, and your vision worsens. Eventually, you may have trouble reading, driving, distinguishing certain colors, and carrying out your regular activities, especially at night.
Stronger lighting and eyeglass adjustments can help when cataracts are small. But eventually, you will 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:
These appear in the center of the lens. They may cause double vision or even multiple copies of an image.
This type affects the edges of the lens, and causes problems with glare.
Posterior Subcapsular Cataracts
These occur on the back of the lens. They reduce your ability to read, even in bright light. They may cause glare or halos around lights at night.
Other kinds of cataracts are grouped according to their causes. They are known as:
- secondary cataracts
- traumatic cataracts
- congenital cataracts
- radiation cataracts.
Updated: March 2012
Posted: March 2012