Cataract Explained

by National Institute on Aging

What is a Cataract?

A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.

A cataract can occur in either or both eyes. It cannot spread from one eye to the other.

Eye diagram

The lens is a clear part of the eye that helps to focus light, or an image, on the retina. The retina is the light-sensitive tissue at the back of the eye.

Normal vision

In a normal eye, light passes through the transparent lens to the retina. Once it reaches the retina, light is changed into nerve signals that are sent to the brain.

Blurry image

The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image you see will be blurred.

Quiz

1. Most cataracts are related to aging.

TRUE is the correct answer. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.

2. A cataract can spread from one eye to the other.

FALSE is the correct answer. A cataract can occur in either or both eyes. It cannot spread from one eye to the other.

3. The retina is a clear part of the eye that helps to focus light.

FALSE is the correct answer. The lens is the clear part of the eye that helps to focus light, or an image, on the retina. The retina is the light-sensitive tissue at the back of the eye.

4. Blurred images occur when a lens becomes cloudy from a cataract.

TRUE is the correct answer. The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image you see will be blurred.

Development and Risk Factors

Age-related cataracts develop in two ways.

• Clumps of protein reduce the sharpness of the image reaching the retina.
• The clear lens slowly changes to a yellowish/brownish color, adding a brownish tint to vision.

The lens consists mostly of water and protein. When the protein clumps up, it clouds the lens and reduces the light that reaches the retina. The clouding may become severe enough to cause blurred vision. Most age-related cataracts develop from protein clumpings.

When a cataract is small, the cloudiness affects only a small part of the lens. You may not notice any changes in your vision. Cataracts tend to grow slowly, so vision gets worse gradually.

Over time, the cloudy area in the lens may get larger, and the cataract may increase in size. Seeing may become more difficult. Your vision may get duller or blurrier.

Cataracts cause the lens to change to a yellowish/brownish color. As the clear lens slowly colors with age, your vision gradually may acquire a brownish shade. At first, the amount of tinting may be small and may not cause a vision problem.

Over time, increased tinting may make it more difficult to read and perform other routine activities. This gradual change in the amount of tinting does not affect the sharpness of the image transmitted to the retina.

If you have advanced lens discoloration, you may not be able to identify blues and purples. You may be wearing what you believe to be a pair of black socks, only to find out from friends that you are wearing purple socks.

The risk of cataract increases as you get older. Other risk factors for cataract include

• certain diseases like diabetes
• personal behavior like smoking or alcohol use
• environmental factors such as prolonged exposure to ultraviolet sunlight.

Quiz

1. The lens is a clear part of the eye that helps to focus light. It is made up of

A. water
B. protein
C. both of the above

C is the correct answer. The lens consists mostly of water and protein. When the protein clumps up, it clouds the lens and reduces the light that reaches the retina.

2. As the clear lens slowly colors with age, your vision gradually may acquire what type of shade?

A. brown
B. green
C. red

A is the correct answer. As the clear lens slowly colors with age, your vision gradually may acquire a brownish shade. At first, the amount of tinting may be small and may not cause a vision problem.

3. If you have advanced lens discoloration, you may not be able to identify which two colors?

A. gray and black
B. orange and red
C. blue and purple

C is the correct answer. If you have advanced lens discoloration, you may not be able to identify blues, and purples. You may be wearing what you believe to be a pair of black socks, only to find out from friends that you are wearing purple socks.

4. The risk of cataract increases as you get older. Other risk factors for cataract include

A. certain diseases
B. personal behavior
C. the environment
D. all of the above

D is the correct answer. The risk of cataract increases as you get older. Other risk factors for cataract include certain diseases such as diabetes, personal behavior such as smoking or alcohol use, and environmental factors such as prolonged exposure to ultraviolet sunlight.

About the Author

www.nia.nih.gov
NIA, one of the 27 Institutes and Centers of NIH, leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life. In 1974, Congress granted authority to form NIA to provide leadership in aging research, training, health information dissemination, and other programs relevant to aging and older people.