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What Are Cataracts?

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Updated April 28, 2014

Cataract illustration

Lens with cataract

ADAM
A cataract is a clouding of the eye's lens. Cataracts are the leading cause of blindness among people older than 55. Most older people have some degree of lens clouding, which is a normal part of aging.

If you wonder what it is like to have a cataract, think about looking through a fogged-up, cloudy window. Cataracts make your visual field appear fuzzy or blurry.

Causes:

A cataract affects the lens of the eye. The lens is located behind the iris. It is responsible for focusing light on the retina, and for producing clear, sharp images. The lens has the ability to change shape, known as accommodation. As the eyes age, however, the lens hardens and loses its ability to accommodate.

The entire lens is contained within a lens capsule. As the eyes age, dead cells accumulate in the lens capsule, causing the lens to gradually become cloudy. Light that would normally be focused by the lens is scattered around because of the cloudiness, so vision is no longer clear and sharp.

Symptoms:

Cataracts are generally painless. They usually start out as a small, opaque spot and slowly grow larger. Vision is not usually affected until a large area of the lens becomes cloudy. The following symptoms may occur with cataracts:

  • Blurred vision
  • Light sensitivity
  • Halos around lights
  • Impaired night vision
  • Yellowing or fading of color vision
  • Double vision
  • Changes in eyewear prescription

Types:

The lens consists of three layers: the outer layer (capsule), the middle layer (cortex) and the inner layer (nucleus). There are three different types of cataracts, distinguished by the part of the lens affected.

Nuclear: This cataract forms in the center of the lens. It occurs because of natural aging, and is usually visible.

Cortical: A cortical cataract forms in the cortex of the lens, beginning with whitish streaks that extend to the front of the lens. These cataracts are commonly seen in diabetic patients.

Subcapsular: These cataracts form in the back of the lens, and usually affect one eye worse than the other.

Risk Factors:

The biggest risk factor for developing cataracts is aging. Clouding of the eye's lens is natural as the eye becomes older. Other risk factors for developing cataracts include:

  • Diabetes
  • Eye surgery
  • Family history of cataracts
  • Smoking
  • Certain medications
  • UV exposure
  • Eye trauma

Additionally, some cataracts are congenital, meaning they formed at birth or during early childhood.

Diagnosis:

These tests help detect cataracts:

Visual acuity test: The eye doctor will measure the sharpness of your vision by having you read letters on a chart from a distance.

Retinal exam: After dilating your eyes, the doctor will use a magnifying lens to carefully examine the inside of the eyes. The lenses will be studied for signs of cataracts.

Tonometry test: Helps determine if there an increase in the eye pressure that could be caused by cataracts.

Additional procedures may be performed to diagnose cataracts including tests to measure glare and contrast sensitivity, night vision, color vision and peripheral vision.

Treatment:

Some cataracts never need treatment, as they remain small and only slightly impair vision. Some people find improvement by wearing stronger glasses, using artificial tears, tinting lenses to reduce glare, and wearing sunglasses. However, patients with significant vision loss due to large cataracts may opt to undergo cataract surgery.

Surgery is the only cure for cataracts. Cataract surgery involves removing the clouded lens and replacing it with a lens implant. Your doctor will decide if only the lens should be removed (extracapsular surgery) or if the entire lens capsule should be replaced (intracapsular surgery).

What You Should Know:

If you have blurry vision, it is important to schedule a comprehensive eye examination to determine the cause. Cataracts may be causing your visual problems, but other eye diseases may result in clouded vision as well. Your eye doctor will perform several diagnostic tests to check the overall health of your eyes. Many eye problems can be prevented or corrected if detected early.

Source: Eyecare America, American Academy of Ophthalmology. Cataracts, May 2007.

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