The term cataract refers to the clouding of the normally transparent crystalline lens within the eye. The word cataract comes from the Greek word for waterfall. Historically it was believed until the mid 1700s that a cataract was formed by opaque material flowing (like a waterfall) into the eye. 

Statistics

Cataract blindness is a major public health problem afflicting 50 million persons worldwide. Cataract develops earlier in life in populations with low income and inferior education. Cataract blindness is a major public health problem in developing countries. 

Between the ages of 52 and 64 one has a 50% chance of having a cataract, there will not be any visual problems until about 65. By 75, most people have a cataract and by age 75 about 50% have some vision loss as a result of cataract. 

Over 1.2 million plastic intraocular lenses are implanted each year during cataract surgery in the United States. The annual cost for cataract surgery in the U.S. (including physician visits) is over $ 3.2 billion and consumes the largest portion of the Medicare budget. It is estimated that the need for cataract extractions would be diminished by half if onset of cataract could be delayed by 10 years.

Etiology

Cataract refers to any opacity of the crystalline lens regardless of whether this opacity interferes with vision. The etiology remains obscure, however, cataracts may be secondary to any condition that interferes with lens metabolism such as trauma, medications, diabetes mellitus, inflammation, chemicals, radiation, heat or cold. The lens is located behind the pupil and its position is maintained by thousands of miniscule chemical strands called zonules. . As the lens opacity or clouding thickens it prevents light rays from passing through the lens and focusing on the retina. Early lens changes may not effect vision, but as the opacity increases changes in vision will occur. These are blurred vision; sensitivity to light and glare; increased nearsightedness; or distorted images

Types of Cataracts

There are three types of cataracts that are characterized by their location on the lens.

Nuclear cataract, the most common type of cataract (the one associated with aging) occurs in the center of the lens. Common symptoms include blurring or dimming of vision, glare and visual distortion and can include myopia (or nearsightedness); temporary improvement of reading vision which disappears as the cataract worsens.

Cortical cataract develops as wedge-shaped spokes in the cortex of the lens. The spokes extend from the outside of the lens to the center. Upon reaching the center of the lens the spokes cause glare and loss of contrast. Many people with diabetes mellitus develop this type of cataract.

Subscapsular cataract starts as a small opacity under the capsule of the lens at the back of the lens. This type of cataract develops slowly and symptoms may not appear until the cataract is well developed. Symptoms include glare and blur. These cataracts are often found in people with diabetes mellitus, high myopia, retinitis pigmentosa and in people taking steroids.

Cataract Symptoms

Cloudy, fuzzy, foggy or filmy vision.

Changes in the way you see colors.

Problems with glare from lamps or the sun.

Frequent changes in your eyeglass prescription.

Double vision.

Better near vision for awhile only in farsighted people.

Cataract Prevention

It is not known exactly why the eye lens changes as we age. Factors that may facilitate the development of cataracts may include:

Ultraviolet radiation or UV light or a lot of time spent in the sun increases the risk of cataract development. In fact, any radiation including beta radiation can exacerbate cataract development. Ophthalmologists now recommend wearing sunglasses and wide-brimmed hats to lessen exposure to ultra-violet light.

Use of steroids, diuretics and tranquilizers are thought to be risk factors for cataract development. However, more studies are needed to differentiate the effect of the disease from the effect of the drugs.

Diabetes mellitus is another risk factor for cataracts.

Cholesterol-inhibiting drugs may be linked to cataracts. The drugs Mevacor, Zocor and Pravachol lower elevated blood cholesterol by inhibiting an early enzyme of cholesterol biosynthesis. Eye lens membrane contains the highest cholesterol content of any known membrane. Because the lens continues to grow throughout life and requires cholesterol, younger patients (especially those less than 40 years) on cholesterol-inhibiting drugs should be monitored for cataract development.

Recent research data indicate that consuming elevated levels of antioxidants such as ascorbate (vitamin-C), carotenoids, and tocopherol (an alcohol that has the properties of vitamin-E) is associated with delayed development of various forms of cataract.

Treatment

The ophthalmologist may prescribe stronger glasses, medication or surgery depending on the symptoms, complications and patient age.

There are three types of surgery to remove lenses that have a cataract:

Extracapsular surgery. The surgeon removes the lens in tact through a 10-12mm incision leaving behind the back half of the capsule (the outer covering of the lens).

Phacoemulsification. The surgeon softens the lens with sound waves and removes it through a needle leaving the back half of the lens behind.

Intracapsular surgery. The surgeon removes the entire lens, including the capsule. This method is rarely used.

In 50% of all cases of extracapsular surgery or Phacoemulsification, the lens capsule becomes cloudy. This cloudiness of the lens capsule usually occurs about one year after surgery and causes vision problems similar to cataract. However, this condition can be treated by a YAG capsulotomy in which the surgeon uses a laser (light) beam to make a tiny hole in the capsule to let light pass. This surgery is painless and can be done on an outpatient basis. Most patients see better after YAG capsulotomy.

Cataract surgery is most often performed under local anesthesia on an outpatient basis. A person who has cataract surgery usually has an artificial plastic intraocular lens implanted in the capsule inside the eye at the same time. Recent surgical improvements are no-stitch surgery, topical anesthesia, surgical correction of astigmatism and new lens designs. It usually takes a few months for the eye to completely heal, but the patient is able to return to normal activity soon after surgery.

Today, approximately 98% of cataract surgery is successful. As a result, millions of Americans have had their quality of life improved in such areas as independence through improved vision, and the ability to work, drive, watch TV and walk safely.

References

Scientific American Medicine, July 1997, 8:IX Common Clinical Disorders in Geriatric Patients (CD-ROM)

Isselbacher K, Braunwald E, Wilson J, Martin J, Fauchi A, Kasper D, Eds. Harrison’s Principles of Internal Medicine, 13^th Edition, McGraw-Hill, New York, 1994, (CD-ROM)

Vaughan D, Asbury T, Tabbara K, General Opthalmology, 12^th Edition, Appleton & Lange, Norwalk, Connecticut/San Mateo, California, 1989

U.S. Department of Health and Human Services, Public Health Service, Agency for Health Care Policy and Research (AHCPR), Cataract in Adults: A Patient’s Guide, February 1993

Taylor A: Cataract: relationship between nutrition and oxidation, Journal of American College of Nutrition, 1993 April, 12:2, 138-46

Taylor A: Associations between nutrition and cataract, Nutrition Review, 1989 August, 47:8, 225-34

Wynn M, Wynn A: Can improved diet contribute to the prevention of cataract?, Nutrition Health, 1996, 11:2, 87-104

Liesegang, TJ: Cataracts and cataract operations (1), Mayo Clinic Proceedings, 1984 August, 59:8, 556-67

Ellwein LB; Kupfer C: Strategic issues in preventing cataract blindness in developing countries., Bulletin of the World Health Organization, 1995, 73:5, 681-90

National Library of Medicine: Cataracts Clinical Guidelines 4 (4), at Internet site:

http://isis.nlm.nih.gov/ahcpr/cat/www/catc4.html

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