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Cataracts

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.

What is the lens?

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.

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.

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.

Are there other types of cataract?

Yes. Although most cataracts are related to aging, there are other types of cataracts:

  • Secondary cataract. Cataracts can form after surgery for other eye problems, such as glaucoma. Cataracts also can develop in people who have other health problems, such as diabetes. Cataracts are sometimes linked to steroid use.


  • Traumatic cataract. Cataracts can develop after an eye injury, sometimes years later.


  • Congenital cataract. Some babies are born with cataracts or develop them in childhood, often in both eyes. These cataracts may be so small that they do not affect vision. If they do, the lenses may need to be removed.


  • Radiation cataract. Cataracts can develop after exposure to some types of radiation.


Eyeball Illustration - Cataracts


Next: What are the causes and risk factors for cataracts? »

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Cataracts

What is the retina?

The retina is an extremely thin tissue that lines the inside of the back of the eye. When we look around, light from the objects we are trying to see enters the eye. The light image is focused onto the retina by the cornea and the lens. This light striking the retina causes a complex biochemical change within layers of the retina and this, in turn, stimulates an electrical response in other layers of the retina. Nerve endings within the retina transmit these signals to the brain through the optic nerve. Within specific areas of the brain, this electrical energy is processed to allow us both to see and to understand what we are seeing. The retina has been compared to the film of a camera. However, film, once used, has a permanent image on it. The retina continually renews itself chemically and electrically, allowing us to see millions of different images every day without them being superimposed.

The retina is about the size of a pos...

Read the Retinal Detachment article »










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