Anatomy of the eye

What is a cataract?

A cataract is a progressive clouding of the normally clear lens of the eye. This clouding can weaken vision. The amount and pattern of cloudiness in the lens, as well as the rate at which it develops, can vary.

What causes a cataract?

The eye functions much like a camera. Light rays enter through the front of the eye, passing through the cornea, the pupil and the aqueous humor (transparent fluid in the front of the eye) onto the lens. The lens then bends light rays to focus objects onto the retina in the back of the eye. From there, the retina, the optic nerve, and the brain process the images and form vision.

Chemical and structural changes occur within the lens over time. These changes make the lens cloudy and prevents light from passing through, which causes some loss of vision. This is a normal part of the aging process.

Cataracts can also progress more rapidly due to:

  • Genetic (inherited) disorders.
  • Medical problems such as diabetes.
  • Certain medications.
  • Injury to the eye.
  • Ultraviolet light and radiation exposure.

Other factors that increase the risk of developing cataracts include cigarette smoke, air pollution and heavy alcohol use.

What are the symptoms of a cataract?

Cataracts are a normal aging change of the eye. Cataracts often form slowly and cause few symptoms. When symptoms are present, they can include:

  • Vision that is cloudy, blurry, foggy or filmy.
  • Glare or light sensitivity (especially when driving at night with oncoming headlights).
  • Prescription changes in glasses (sudden nearsightedness).
  • Double vision in one eye.
  • Need for brighter light to read.
  • Poor night vision.
  • Changes in the way you see color.

Last reviewed by a Cleveland Clinic medical professional on 07/03/2018.


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