Encyclopedia / C / Cataracts


What Are Cataracts?

A cataract is a loss of transparency in the normally clear lens of the eye. At first, the onset of cataracts may only result in the need to get stronger prescription glasses; less often, a small, hazy spot may appear in the field of vision. Gradually (often over a period of years), as the lens grows more opaque, vision becomes blurrier, especially at night or in very bright light. The level of cataract maturity at which a particular patient needs cataract surgery varies from patient to patient. Some people have difficulty functioning visually from a relatively mild cataract; others can have significantly advanced cataracts and yet still not have enough problems to need surgery.  Because even advanced cataracts can be still be successfully treated with surgery, cataract surgery can be postponed until the patient has difficulty with tasks of daily living from cataract-related visual symptoms.

About 75% of Americans over age 60 show some signs of cataracts. Until recently, cataracts were thought to be an inevitable part of growing older: As you age, the lens of your eye becomes cloudier. While this is true to a certain extent, there is hope that, with good health habits, you may be able to postpone the onset of cataracts, and for some patients this may mean not ever having cataract symptoms significant enough to require surgery.

**Who Gets Cataracts? **

In the United States, about 50% of those between the ages 65 and 74, and 70% of those over age 75 have a cataract. Women are affected more frequently than men. African Americans lose their vision from cataracts and glaucoma at twice the rate of Caucasian Americans, primarily due to lack of treatment.

One in every 10,000 babies is born with congenital cataracts. In some cases, it is related to the mother having an infectious disease or engaging in alcohol or drug abuse during pregnancy.


  • Gradual, painless, increasingly blurred or double vision.

  • Halos or blurriness around lights. Vision may actually be better in dim light, since bright light causes the pupil to constrict and increases the passage of light through the part of the lens most affected by a cataract.

  • Increased sensitivity to light and glare.

  • Dulled color perception.

  • Temporary improvement in near vision without glasses (patient may no longer need reading glasses for a brief period of time).

  • Frequent changes in eyeglass or contact lens prescriptions.

  • Difficulty driving at night or in bright light.

  • Yellowish or dingy tint to objects in the vision of an eye with a cataract.

Causes/Risk Factors

  • Aging is the single greatest risk factor for cataracts, as cumulative exposure to the sun’s ultraviolet rays over a lifetime appears to be a primary cause.

  • Exposure to radiation, including x-rays and microwaves, may promote cataracts.

  • Physical injury to or inflammation of the eye (for example, uveitis or iritis) may lead to cataracts.

  • The long-term use of corticosteroid drugs, hereditary factors, and birth defects may be contributing factors.

  • Cataracts may occur at a younger age in people with diabetes mellitus.

  • Smoking may increase the risk for cataract formation, and the risk rises as the cumulative amount of smoking increases.

What If You Do Nothing?

Cataracts will usually worsen gradually, and eventually you may need surgery to correct the problem. But in most cases cataracts develop very slowly, and by avoiding risk factors for cataract formation you may be able to postpone surgery or avoid it altogether. In recent years increasing knowledge about the risk factors for cataracts makes it likely that their rate of progression can be slowed even further.

**Diagnosis **

To detect a cataract, an eye care professional examines the lens using a slit lamp microscope. This microscope has a light attached, which allows the doctor to examine the cornea, iris, and lens under high magnification. Pupil dilation (the pupil is widened after administering eye drops) allows the doctor to see the lens and retina better.

Visual acuity at various distances is determined using the standard eye chart. The examination helps detect vision loss due to a cataract.

The lens consists of three parts: the nucleus (center of the lens), the lens cortex (periphery), and the capsule (membrane that envelops the lens). Cataracts can form in any of these parts, and it is possible for a person to have more than one type of cataract in the same eye.

Nuclear cataracts develop in the nucleus and are the type most commonly found in older patients. They can take years to develop and often give the nucleus a yellow tint. The incidence of nuclear cataracts increases with age and cigarette smoking.

Cortical cataracts form in the lens cortex (peripheral area). They eventually extend like spokes on a wheel into the nucleus of the lens. This type of cataract is related to lifetime exposure to ultraviolet light.

Subcapsular cataracts develop in the envelope of the lens, and often in the center. The onset of this type is rapid and symptoms can develop over months, rather than years. This type of cataract is often the result of prolonged use of corticosteroids (such as prednisone), inflammation, trauma, or diabetes.  This particular type of cataract is also characteristically associated with a higher incidence of difficulty functioning in glare conditions as well as increased difficulty reading.


  • To minimize glare symptoms outdoors, wear a wide-brimmed hat and sunglasses.

  • Indoors, use floor or desk lamps with incandescent bulbs instead of ceiling or fluorescent lights. Avoid pinpoint halogen lights, which cause the pupils to constrict. Installing dimmer controls is advised.

  • When reading, try large-print books and newspapers.

  • Surgery (successful in 95% of cases) is the only cure for cataracts. It can often be postponed indefinitely but is advised when cataracts interfere with normal activities.

Two surgical procedures can be used to remove a cataract: phacoemulsification and extracapsular surgery:

Phacoemulsification is the most commonly used procedure. Small incisions are made on the side of the cornea and a tiny probe is inserted into the eye. This probe emits an ultrasound wave that softens and breaks up the cataract. The debris is then removed by suction.  Since the advent of phacoemulsification, it has become the standard of care in cataract surgery; this is because the incisions in the eye used in phacoemulsification cataract surgery are usually small enough to not require stitches to close and because they heal more quickly, and with fewer complications, than larger incisions from extracapsular cataract surgery.

Extracapsular surgery requires a longer incision in the cornea. The hard center of the lens is removed in one piece and the rest of the lens is suctioned out.  Because a larger incision is made than in phacoemulsification surgery, numerous sutures are required to close the corneal incision.  This can result in a longer healing time and a significant amount of astigmatism generated in the cornea (an asymmetric bend in the cornea that distorts vision if not corrected with glasses).

Replacing the lens. Regardless of the method used to remove the natural lens with the cataract, the lens is then replaced with an intraocular lens (IOL), a clear, artificial lens that becomes a permanent part of the eye. The IOL is usually made of acrylic, silicone, or, less commonly, a plastic called PMMA. The replacement of the natural lens with an artificial lens allows light to be focused on the retina without scattering or discoloring the light, resulting in improved vision. The artificial lens does not require additional care, and the eye looks and feels normal.

Patients who are unable to have an IOL inserted because of eye disease or other complications can use soft contact lenses or glasses with powerful magnification.

Once the eye has healed, patients with an IOL usually update their eyeglass prescription. The most commonly used IOL is a monofocal (single focus lens) implant, meaning that it cannot change shape (accommodate) in order to bring both near and far objects into focus. The IOL power is chosen by the surgeon to reflect the desire of the patient to see most clearly at either distance or near when not wearing glasses after the surgery. Most patients choose to have an IOL with a power that allows them to see as clearly as possible for distance vision without glasses—in which case glasses are usually required for reading and close work.

Another option is to have the IOL power in one lens focused for near vision and the lens in the other eye focused for distance vision, generally avoiding the need for eyeglasses for most visual tasks during the day. This is known as monovision. The drawback to monovision is that it can compromise depth perception. Because of this downside, most patients do not do well with monovision unless they have had a history of functioning with this type of visual arrangement in the past, either naturally or through the use of contact lenses.

A third option is to use a presbyopia-correcting (as in reading glasses) IOL, which generally provides much more freedom from glasses or contact lenses for near, intermediate, and distance vision tasks than a monofocal IOL. Most presbyopia-correcting IOLs are multifocal, which allows for clearer vision at all distances simultaneously, without the need of the IOL to change shape. Because IOLs of this variety can be selected to have similar power between the two eyes, better depth perception and fewer visual compromises are possible with multifocal IOLs compared with monovision lenses.  However, there are common side effects with many multifocal IOLs. These include halos and glare (which usually resolve after several weeks to a few months), as well as the need for a period of time (usually several weeks to a few months) for the brain to learn how to adapt to this different way of focusing (neuro-adaptation).

Following surgery, patients often see a blue tint around objects or they may experience a significantly more vibrant array of colors in their vision. A cataract blocks colors such as the blues and violets at the lower end of the color spectrum, so that when the cataract is removed, these colors once again become vivid.


  • Wear ultraviolet-protective sunglasses. This is the most important step you can take to prevent additional damage to your eyes. Sunglasses with lenses tinted yellow, brown, or amber will absorb blue light, which is the light most readily scattered—and so transformed into glare—by incipient cataracts. Choose sunglasses that indicate they block at least 95% of ultraviolet-B (UVB) rays. When boating or participating in water sports, wearing polarized sunglasses can decrease exposure to significantly stronger ultraviolet rays.
  • If you smoke, quit. While the exact ways in which smoking causes cataract formation are not known, smokers are approximately twice as likely to develop cataracts as nonsmokers.
  • Eat a diet high in carotenoids. Two large studies of healthcare professionals suggest that foods rich in two carotenoids, lutein and zeaxanthin, are associated with a lower risk of cataracts. The best sources for lutein are corn, kale, spinach, and other dark leafy greens, pumpkin, zucchini, yellow squash, red grapes, and green peas; for zeaxanthin, orange bell peppers, oranges, corn, honeydew melon, and mango. (Of course, these are not the only beneficial carotenoids you should eat, but they scored high in this study.)

When To Call Your Doctor

If you notice any symptoms of cataracts, consult your ophthalmologist.

Reviewed by Daniel E. Bustos, M.D., M.S., Private Practice specializing in Comprehensive Ophthalmology in Nashville, TN. Review provided by VeriMed Healthcare Network.