The human eye has several parts. The outer layer of the eyeball consists of a transparent dome-shaped cornea and an opaque white sclera, which is a fibrous membrane. The cornea and sclera help protect the eye. The next layer includes the iris, pupil, and ciliary body. The iris is the colored part of the eye; the pupil is the small dark round hole in the middle of the iris. The pupil and iris allow light into the eye. The ciliary body contains muscles that help the eye to focus. The lens lies behind the pupil and iris. It is covered by a cellophane-like capsule. The lens is normally transparent, elliptical in shape, and somewhat elastic. This elasticity allows the lens to focus on both near and far objects. The lens is attached to the ciliary body by fibers (zonules of Zinn). Muscles in the ciliary body act on the zonules, which then change
The lens is made up of approximately 35% protein and 65% water. As people age, the proteins in the lens begin to degenerate. Changes in the proteins, water content, enzymes, and other chemicals are some of the causes of cataract formation.
The major parts of the lens are the nucleus, the cortex, and the capsule. The nucleus is in the center of the lens, the cortex surrounds the nucleus, and the capsule is the outer layer. Opaque areas can develop in any part of the lens. Cataracts, then, can be classified according to location (nuclear, cortical, or posterior subcapular cataracts). The density and location of the cataract determines the extent of vision affected. If the cataract forms in the area of the lens directly behind the pupil, the person's vision may be significantly impaired. A cataract that occurs on the outer edges or side of the lens will cause less severe impairment.
Cataracts in the elderly are so common that they are considered a normal part of the aging process. People between the ages of 52–64 have a 50% chance of developing a cataract, while at least 70% of those 70 and older are affected. Cataracts associated with aging (senile or age-related cataracts) most often occur in both eyes, with each cataract progressing at a different rate. At first, these cataracts may not affect vision. If the cataract remains small or at the periphery of the lens, the visual changes may be minor.
Cataracts that occur in people other than the elderly are much less common. Congenital cataracts occur very rarely in newborns. Genetic defects or an infection or disease in the mother during pregnancy are among the causes of congenital cataracts. There is a condition called blue cataracts, which is inheritance-linked and affects primarily Tibetans and some other Asians. Traumatic cataracts may develop after an injury or foreign body damages the lens or eye. Systemic illnesses like diabetes may result in cataracts. Cataracts can also occur secondary to other eye diseases—for example, an inflammation of the inner layer of the eye (uveitis) or glaucoma. Such cataracts are called complicated cataracts. Toxic cataracts result from chemical toxicity, such as steroid use. Cataracts can also result from exposure to the sun's ultraviolet (UV) rays.
Causes & symptoms
Recent studies have been conducted to determine whether diet or the use of vitamins might have an effect on the formation of cataracts in older people. Although debate continues, several studies reported in late 2001 that a diet rich in certain caretenoids may protect against development of cataracts. Likewise, there has been considerable interest in the use of antioxidant supplements as a protection against cataracts. Such antioxidant vitamins as vitamins A, C, E, and beta-carotene protect body tissues against free radicals, which are byproducts of oxidation. Vitamin C in particular, has shown the strongest impact on lower rates of cataracts. Some vitamins are marketed specifically for the eyes. Patients should speak to their doctors about the use of such vitamins.
Studies also have recently linked changes in lens proteins to cataract formation. Soluble proteins in the lens begin to condense and form clumps, leading to cataracts. Researchers have identified mutations in genes that likely lead to protein changes resulting in juvenile cataracts. The next step is to study a possible genetic relationship to formation of age-related cataracts as well.
Smoking and alcohol intake have been implicated in cataract formation. Some studies have determined that a diet high in fat will increase the likelihood of cataract formation, while eating more foods rich in antioxidants will lower the risk. More research is needed to determine if diet, smoking, alcohol consumption, or vitamins have any connection to the formation of cataracts.
Cataracts may have the following symptoms:
- gradual, painless onset of blurry, filmy, or fuzzy vision
- poor central vision
- frequent changes in eyeglass prescription
- changes in color vision
- increased glare from lights, especially oncoming headlights when driving at night
- "second sight" improvement in near vision (no longer needing reading glasses), but a decrease in distance vision
- spoor vision in sunlight
- the presence of a milky whiteness in the pupil as the cataract progresses
Both ophthalmologists and optometrists may detect and monitor cataract growth and prescribe prescription lenses for visual deficits. Only an ophthalmologist, however, can perform cataract extraction.
Cataracts are easily diagnosed from the reporting of symptoms, a visual acuity examination using an eye chart, and by a physician or optometrist's examination of the eye. Shining a penlight into the pupil may reveal opacities or a color change of the lens even before the patient develops visual symptoms. A slit lamp, which is basically a large microscope, allows the doctor to examine the front of the eye and the lens, and to determine the location of the cataract.
Some other diagnostic tests may be used to determine if cataracts are present or how much improvement the patient may have after surgery. These tests include a glare test, potential vision test, and contrast sensitivity test.
Because free radicals have been implicated as a cause of cataracts, alternative therapies emphasize the importance of a healthful diet, nutritional supplements and/or herbal remedies to prevent and slow down the progression of cataracts.
A naturopathic doctor or a nutritionist may recommend the following dietary changes:
- Reduce consumption of salty or fatty foods. Diabetics should also limit their intake of milk and other dairy products.
- Increase intake of foods that are high in beta-carotene: peaches, apricots, berries, carrots, and leafy green vegetables. Beta-carotene and other antioxidants can protect against or slow down the development of cataracts.
- Stop cigarette smoking and avoid exposure to secondhand smoke.
- Eat a diet rich in fruits and vegetables with high concentrations of vitamin C. Take supplemental vitamin C (1 g three times daily) and vitamin A (25,000 IU per day).
- Take supplemental beta-carotene (25,000–100,000 IU per day) and selenium (400 mcg per day). Low selenium levels may increase the risk of cataracts.
- Increase intake of L-cysteine (400 mg per day), L-glutamine (200 mg per day), and L-glycine (200 mg per day). These three amino acids may be beneficial to some cataract patients.
- Add other supplements: zinc, lutein, riboflavin, and cod liver oil.
There are two herbal remedies that may help protect the eyes against cataracts:
- Bilberries (40–80 mg daily). Early research indicates that eating bilberries may halt cataract progression.
- Hachimijiogan. Hachimijiogan is an ancient Chinese herbal formula. Animal studies suggest that it may protect the eyes against cataracts by increasing the glutathione content of the lens.
Cataracts that cause no symptoms or only minor visual changes may not require any treatment. An ophthalmologist or optometrist should continue to monitor and assess the cataract at scheduled office visits. Stronger prescription eyeglasses or contact lenses may be helpful.
Cataract surgery is the only option for patients whose cataracts interfere with vision to the extent of affecting their daily lives. It is the most frequently performed surgery in the United States. It generally improves vision in over 90% of patients. Some people have heard that a cataract should be "ripe" before being removed. A "ripe" or mature cataract means that the lens is completely opaque. Most cataracts are removed before they reach that stage. Sometimes cataracts need to be removed so that the doctor can examine the back of the eye more carefully. Patients with diseases that may affect the eye may require cataract surgery for this reason. If cataracts are present in both eyes, only one eye at a time should be operated on. Healing occurs in the first eye before the second cataract is removed, sometimes as early as the following week. A final eyeglass prescription is usually given about four to six weeks after surgery. Patients will still need reading glasses. The overall health of the patient needs to be considered in making the decision to operate. Age alone, however, need not preclude
Patients are given antibiotic drops to prevent infection and steroids to reduce inflammation after surgery. An eye shield or glasses during the day will protect the eye from injury while it heals. At night, the patient should wear an eye shield. The patient returns to the doctor the day after surgery for assessment, with several follow-up visits over the next two months to monitor the healing process.
The success rate of cataract extraction is very high, with a good prognosis. Visual acuity of 20/40 or better may be achieved. If an extracapsular cataract extraction was performed, a secondary cataract may develop in the remaining back portion of the capsule one to two years after surgery. YAG capsulotomy is most often used to treat this type of cataract. YAG stands for yttrium aluminum garnet, the name of the laser used for this procedure. The laser beam makes a small opening in the remaining back part of the capsule, allowing light through.
Complications occur in a very small percentage (3–5%) of surgical cataract extractions. Infections, swelling of the cornea (edema), bleeding, retinal detachment, and the onset of glaucoma have been reported. Any haziness, redness, decrease in vision, nausea, or pain should be reported to the surgeon immediately.
Preventive measures emphasize protecting the eyes from UV radiation by wearing glasses with a special coating to protect against UV rays. Dark lenses alone are not sufficient. The lenses must protect against UV light (specifically, UV-A and UV-B). Antioxidants and herbal remedies may also provide some protection by reducing free radicals that can damage lens proteins. A healthful diet rich in sources of antioxidants, including citrus fruits, sweet potatoes, carrots, green leafy vegetables, and/or vitamin supplements may be helpful. When taking certain medications, such as steroids, more frequent eye exams may be necessary. Patients should speak to their doctors to see if medications may affect their eyes.
"Cataract." Medical-Surgical Nursing: Concepts and Clinical Practice, fifth edition. Edited by Wilma J. Phipps et al. St. Louis, MO: Mosby-Year Book, Inc., 1995.
Liberman, Shari, and Nancy Bruning. The Real Vitamin & Mineral Book: Using Supplements for Optimal Health,, 2nd ed. Garden City Park, NY: Avery Publishing Group, 1997.
Murray, Michael, and Joseph Pizzorno. Encyclopedia of Natural Medicine. Revised second ed. Rocklin, CA: Prima Health, 1997.
Friedrich, MJ. "Insight Into Opacity: Clues to Cataract Formation." JAMA, The Journal of the American Medical Association 286 no. 14 (October 10, 2001): 1705.
"Nutrients May Prevent Age-Related Eye Diseases." Health and Medicine Week (November 26,2001): 2.
American Academy of Ophthalmology (National Eyecare Project). P.O. Box 429098. San Francisco, CA 94142-9098. (800) 222-EYES. http://www.eyenet.org.
American Optometric Association. 243 North Lindbergh Blvd. St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.
The Lighthouse. 111 East 59th Street. New York, NY 10022. (800) 334-5497. http://www.lighthouse.org.
Prevent Blindness America. 500 East Remington Road. Schaumburg, IL 60173. (800) 331-2020. http://www.prevent-blindness.org.
Teresa G. Odle