What Causes Cataracts?

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, most elderly 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.
Image of the eye

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.
The eye functions much like a camera. Light rays enter the eye, passing through the cornea, the aqueous humor -- transparent fluid in the front of the eye -- and then the pupil and into the lens. The lens bends the light rays to focus objects onto the retina lining the back of the eye. From there, the image passes through the retinal cells, into the optic nerve, and finally to the back of the brain which process the images.  Cataracts occur when there is a buildup of protein in the lens that makes it cloudy. This prevents light from passing clearly through the lens, causing some loss of vision. Since new lens cells form on the outside of the lens, all the older cells are compacted into the center of the lens resulting in the cataract.
Types of cataracts include:
  • Age-related cataracts. As the name suggests, this type of cataract develops as a result of aging.
  • Congenital cataracts. Babies are sometimes born with cataracts as a result of an infection, injury, or poor development before they were born, or they may develop during childhood.
  • Secondary cataracts. These develop as a result of other medical conditions, like diabetes, or exposure to toxic substances, certain drugs (such as corticosteroids or diuretics), ultraviolet light, or radiation.
  • Traumatic cataracts. These form after injury to the eye.
Other factors that can increase a person's risk of developing cataracts include cigarette smoke, air pollution, and heavy alcohol consumption
Cataracts Eyes

What causes cataracts?

The lens lies behind the iris and the pupil. It works much like a camera lens. It focuses light onto the retina at the back of the eye, where an image is recorded. The lens also adjusts the eye’s focus, letting us see things clearly both up close and far away. The lens is made of mostly water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it.
But as we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract. Over time, the cataract may grow larger and cloud more of the lens, making it harder to see.
Researchers suspect that there are several causes of cataract, such as smoking and diabetes. Or, it may be that the protein in the lens just changes from the wear and tear it takes over the years.

How can cataracts affect my vision?

Age-related cataracts can affect your vision in two ways:
  1. Clumps of protein reduce the sharpness of the image reaching the retina. 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.
  2. The clear lens slowly changes to a yellowish/brownish color, adding a brownish tint to vision. 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.

What Are the Symptoms of Cataracts?

Cataracts usually form slowly and cause few symptoms until they noticeably block light. When symptoms are present, they can include:
  • Vision that is cloudy, blurry, foggy, or filmy
  • Progressive nearsightedness in older people often called "second sight" because they may no longer need reading glasses.
  • Changes in the way you see color because the discolored lens acts as a filter.
  • Problems driving at night such as glare from oncoming headlights.
  • Problems with glare during the day.
  • Double vision (like a superimposed image).
  • Sudden changes in glasses prescription.
    • How Are Cataracts Diagnosed?


      An eye exam will be given to test how well you can see (remember to bring your glasses or wear your contacts to the appointment). Your doctor will also dilate your pupil in order to examine the condition of the lens and other parts of the eye.

      How Are Cataracts Treated?

      If your vision can be corrected to an acceptable level with a change in prescription, eyeglasses, including bifocals or contacts, may be prescribed, eliminating the need for surgery at that time.
      If your vision loss cannot be corrected with new glasses and cataracts interfere with your daily life, you may be a candidate for cataract surgery, which involves removing the clouded lens and replacing it with a clear, artificial one.
      Cataract surgery is usually conducted on an outpatient basis and is very successful in restoring vision. It is the most frequently performed surgery in the U.S., with more than 1.5 million cataract surgeries done each year. Better than nine out of 10 people who have cataract surgery have improvement in vision.
      Talk to your doctor to see which treatment is right for you.

      Can Cataracts Be Prevented?

      Because the exact cause of cataracts is uncertain, there is no proven method of preventing them. Because cataracts and other conditions such as glaucoma are common in older adults, it's important to have your eyes examined on a regular basis.
      This is particularly important if you have risk factors or a family history of eye problems. Adults should see an eye doctor at least every two years and annually after age 50.
      People with a history of eye problems or other medical conditions that increase the risk of eye disease -- such as diabetes -- may need eye exams more frequently.
      Be sure to ask your doctor if you have any risk factors or indications that cataracts or other conditions may affect your vision.
       

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