Alternative names
Lens opacity

A cataract is a cloudy or opaque area in the lens of the eye.

Causes, incidence, and risk factors

The lens of an eye is normally clear. If the lens becomes cloudy, the condition is known as a cataract. Rarely, cataracts may be present at or shortly after birth. These are called congenital cataracts.

Adult cataracts usually develop with advancing age and may run in families. Cataracts are accelerated by environmental factors, such as smoking or exposure to other toxic substances, or they may develop at any time after an eye injury. Metabolic diseases such as diabetes also greatly increase the risk for cataracts. Certain medications, such as cortisone, can also accelerate cataract formation.

Congenital cataracts may be inherited. The gene for such cataracts is dominant (autosomal dominant inheritance), which means that the defective gene will cause the condition even if only one parent passes it along. Approximately 50% of children in such families will be affected.

Congenital cataracts can also be caused by infections of the mother during pregnancy such as rubella, or associated with metabolic disorders such as galactosemia. Risk factors include inherited metabolic diseases, a family history of cataracts, and maternal viral infection.

Adult cataracts are generally associated with aging. They develop slowly and painlessly with a gradual onset of difficulty with vision.

Visual problems may include the following changes:

  • Difficulty seeing at night  
  • Seeing halos around lights  
  • Being sensitive to glare

Vision problems associated with cataracts generally progress to decreased visual acuity, even in daylight.

Adult cataracts are classified as immature, mature, and hypermature. A lens that has some remaining clear areas is referred to as an immature cataract. A mature cataract is completely opaque. A hypermature cataract has a liquefied surface that leaks through the capsule and may cause inflammation of other structures in the eye.

Most people develop some clouding of the lens after the age of 60. About 50% of people aged 65-74 and about 70% of those 75 and older have visually significant cataracts.

Most people with cataracts have similar changes in both eyes, although one eye may be worse than the other. Many people with this condition have only minimal visual changes and are not aware of their cataracts.

Factors that may contribute to cataract development are low serum calcium levels, diabetes, long-term use of corticosteroids, and various inflammatory and metabolic disorders. Environmental causes include trauma, radiation exposure, and excessive exposure to ultraviolet light (sunlight).

In many cases, the cause of cataract is unknown.


  • Cloudy, fuzzy, foggy, or filmy vision  
  • Loss of color intensity  
  • Frequent changes in eyeglass prescription  
  • Impaired vision at night, especially while driving, caused by glare from bright lights  
  • Problems with glare from lamps or the sun  
  • Halos around lights  
  • Double vision in one eye  
  • Decreased contrast sensitivity

Signs and tests

  • Standard ophthalmic exam, including slit lamp examination  
  • Ultrasonography of the eye in preparation for cataract surgery

Other tests that may be done (rarely) include:

  • Glare test  
  • Contrast sensitivity test  
  • Potential vision test  
  • Specular microscopy of the cornea in preparation for cataract surgery


The only treatment for cataract is surgical removal. This is done when a person cannot see well enough with glasses to perform normal activities. For some people, changing glasses, getting stronger bifocals, or using a magnifying lens is helpful enough. Others choose to have cataract surgery.

If a cataract is not bothersome, then surgery is usually not necessary. Sometimes there is an additional eye problem that cannot be treated without first proceeding with cataract surgery.

Cataract surgery consists of removing the lens of the eye and replacing it with an artificial lens. A cataract surgeon will discuss the options with the patient, and together they will decide which type of removal and lens replacement is best.


There are 2 types of surgery that can be used to remove lenses that have a cataract.

Extracapsular surgery consists of surgically removing the lens, but leaving the back half of the capsule (the outer covering of the lens) intact. High-frequency sound waves (phacoemulsification) may be used to soften the lens to facilitate removal through a smaller incision.

Intracapsular surgery involves surgically removing the entire lens, including the capsule. Today this procedure is done very rarely.


People who have cataract surgery are usually fitted with an artificial lens at the same time. The artificial lens is a synthetic disc called an intraocular lens. It is usually placed in the lens capsule inside the eye.

Other options include contact lenses and cataract glasses.

Surgery can be done in an outpatient center or hospital. Most people do not need to stay overnight in a hospital. The patient will need a friend or family member to assist with travel and home care after outpatient surgery. Follow-up care by the surgeon is important.

Expectations (prognosis)
For most people, cataract surgery has a low risk of complications. With implanted artificial lenses, most people no longer need corrective lenses for distance vision. Glasses are usually necessary for reading.


Vision may not improve to 20/20 after cataract surgery if other eye diseases such as macular degeneration are present. Ophthalmologists can usually, but not always, determine this in advance.

In infants, amblyopia and decreased visual development may occur as a result of cataracts. Early diagnosis and treatment is essential.

Calling your health care provider

Call for an appointment with your health care provider if you have symptoms such as progressive deterioration of vision, decreased night vision, or problems with glare.

Also call if you have a family history of congenital cataracts or if your child has symptoms or signs suggestive of a cataract.


The primary prevention involves controlling associated diseases and avoiding exposure to factors known to promote cataract formation.

Wearing sunglasses when you are outside during the day can reduce the amount of UV light your eyes are exposed to. Some sunglasses do not filter out the harmful UV. An optician should be able to tell you which sunglasses filter out the most UV. For patients who smoke cigarettes, quitting will decrease the risk of cataracts.

Johns Hopkins patient information

Last revised: December 2, 2012
by Arthur A. Poghosian, M.D.

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