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Normally, the lens of your eye is clear. But if you have a cataract, it means you have a cloudy spot in your lens.

As the cataract grows, your sight gets blurry or misty.^{1 2} You might feel as if you're looking through glasses that are dirty or scratched. It's just like a camera lens that's gotten scratched. The marks would show up on the pictures.

Cataracts are common. They can happen at any age, but most form as people get older.

If you have a cataract, you shouldn't worry. It might not bother you at first. And when it does, you can have an operation to take it out. You should be able to see much better afterward.

• One-third of people over the age of 65 have cataracts. And about half of people have them by the age of 75.
• Most cataracts are caused by aging.
• Your chances of getting cataracts as you get older can be higher because of the way you live. For example, your chances are higher if you smoke or you go out in the sun a lot.
• But cataracts can be caused by other things. You can be born with them or get them because of health problems such as diabetes.
• Surgery is the only treatment for cataracts that we know works.
• You should be able to see much better and enjoy life more after surgery. But there are risks, and your eyesight probably won't be perfect.

The front of your eye has a thin film over it. This film is called the cornea. The cornea helps to stop your eye from getting damaged.

The hole in the center of your eye is the pupil. It lets light in.

The part of your eye that focuses light is the lens. It helps you see things clearly.^{1 2} Normally, your lens is clear.

The lens sits behind the colored part of your eye, called the iris. The lens is held in place by tissue known as the capsule.

The back of your eye is called the retina. It has nerve cells that pick up light.

This is what happens when you look at something.

• Light comes into your eye through the hole in the center (your pupil).
• The light goes through your lens.
• The lens focuses the light onto the back of your eye (your retina), making a picture.
• The nerve cells there pick up the picture and send signals to your brain.
• Your brain tells you what you are seeing.

Your lens must be clear for your retina to get a sharp picture.

If you have a cataract, the lens in your eye has turned cloudy.^{1 2} This makes the picture on the back of your eye blurry. It's like looking through a dirty windshield or frosted glass.

The cataract is the cloudy part of your lens. It is not a layer of skin that grows over your eye and can be peeled off, as some people think.

Most cataracts are caused by aging. Doctors sometimes call these senile cataracts or age-related cataracts.

As you get older, your lens can change in two ways:²

• Your lens might get clumps in it. Your lens is made up mostly of water and protein. As you get older, the protein can clump up and cloud your lens. Then less light reaches the back of your eye. Your vision might get blurry.
• Your lens might change color. When you are younger, your lens doesn't have any color. But as you get older, it slowly turns yellow-brown. You might find it harder to see some colors, such as blues and purples. But this change doesn't make your vision blurry.

Different parts of your lens can get cloudy, so you can get different types of cataract. To decide which type of cataract you have, your doctor will check where in your lens your cataract has started. Your symptoms will depend on the type of cataract you have.^{3 4}

• Some cataracts begin around the edges of your lens and grow in a pattern like the spokes of a wheel. Doctors call these cortical cataracts. When you look at bright lights, you get a lot of glare or see a ring around the light. Or you might have these symptoms when the sun is low in the sky. If you drive, you might find that headlights coming at you bother you more than before.
• Other cataracts happen when the middle of your lens turns yellow-brown and gets harder. Doctors call these nuclear cataracts. Your vision might get blurry.
• Some cataracts happen when grainy cells get between the back of your lens and the capsule. This can cause bad glare from lights. Doctors call these posterior subcapsular cataracts. They can develop when you are younger.

You can have a combination of any of these three kinds of cataracts. This is known as a mixed cataract. Almost one-third of eyes with cataracts have a mixture of types.^{3 4}

You can get a cataract in just one eye, although most people get them in both eyes. But cataracts don't spread from one eye to the other. You don't catch them like an infection.

Most cataracts are caused by aging. But other things can cause them.² To read more, see Other causes of cataracts.

We don't know exactly why some people get cataracts as they age and others don't. And we don't know why some people's cataracts get worse faster. There are probably many reasons.

We do know there are some things that make it more likely that you will get cataracts as you age. Doctors call these risk factors. Risk factors for cataracts include:

• Smoking a lot
• Having cataracts run in your family
• Getting very dehydrated at some point in your life (for example, having severe diarrhea can make you dehydrated)
• Taking drugs called steroids for a long time
• Being in the sun a lot
• Having high blood pressure or heart disease.

To read more, see Risk factors for cataracts.