A cataract is a cloudiness or opacity in the normally transparent crystallinelens of the eye. Changes in the proteins, water content, enzymes, andother chemicals of the eye and lens are some of the reasons for the formation of a cataract. This cloudiness can cause a decrease in vision and may leadto eventual blindness.
Cataracts in the elderly are so common that they are thought to be a normal part of the aging process. Between the ages of 52-64, there is a 50% chance ofhaving 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. Initially, cataracts may not affect vision. If the cataract remains small or at theperiphery 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. Traumatic cataracts may develop after a foreign body or trauma injures the lens or eye. Systemic illnesses, such as diabetes, may resultin cataracts. Cataracts can also occur with other eye diseases--for example,an inflammation of the inner layer of the eye or glaucoma. Such cataracts arecalled 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.
Both ophthalmologists and optometrists may detect and monitor cataract growthand prescribe prescription lenses for visual deficits. However, only an ophthalmologist can perform cataract extraction. Cataracts are easily diagnosed from the reporting of symptoms, a visual acuity exam using an eye chart, and by examination of the eye itself. Shining a penlight into the pupil may revealopacities or a color change of the lens even before visual symptoms have developed. An instrument called a slit lamp is basically a large microscope. This lets the doctor examine the front of the eye and the lens. The slit lamp helps the doctor determine the location of the cataract. Other diagnostic testsinclude a glare test, potential vision test, and contrast sensitivity test.
For cataracts that cause no symptoms or only minor visual changes, no treatment may be necessary. Continued monitoring and assessment of the cataract is needed by an ophthalmologist or optometrist at scheduled office visits. Increased strength in prescription eyeglasses or contact lenses may be helpful. This may be all that is required if the cataract does not reduce the patient's quality of life.
Cataract surgery--the only option for patients whose cataracts interfere withvision to the extent of affecting their daily lives--is the most frequentlyperformed surgery in the United States. There are two types of cataract surgery: intracapsular and extracapsular. Intracapsular surgery is the removal ofboth the lens and the thin capsule that surround them. This type of surgery was common before 1980, but has since been displaced by extracapsular surgery.Removal of the capsule requires a large incision and doesn't allow comfortable intraocular lens implantation. Thus, people who undergo intracapsular cataract surgery have long recovery periods and have to wear very thick glasses.
Extracapsular cataract surgery is the removal of the lens where the capsule is left in place. Each year in the United States, over a million cataracts areremoved this way. Phacoemulsification, a type of extracapsular extraction that uses ultrasonic vibration to break the cataract up into very small pieceswhich are suctioned out of the eye, needs a very small incision, resulting infaster healing.
A replacement lens is usually inserted at the time of the surgery. A plasticartificial lens called an intraocular lens (IOL) is placed in the remaining posterior lens capsule of the eye. When the intracapsular extraction method isused, an IOL may be clipped onto the iris. Contact lenses and cataract glasses (aphakic lenses) are prescribed if an IOL was not inserted.
Cataract surgery itself is quite safe; over 90% of the time, there are no complications. The success rate of cataract extraction is very high, with a goodprognosis. Ordinarily, patients experience improved visual acuity and improved perception of the vividness of colors, leading to increased abilities in many activities, including reading, needlework, driving, golf, and tennis, forexample. In addition, sometimes implanted corrective lenses eliminate the need for eyeglasses or contact lenses. A visual acuity of 20/40 or better may be achieved.
Glasses with a special coating to protect against ultraviolet (UV) rays may help to prevent cataracts. Antioxidants may also provide some protection by reducing the free radicals that can damage lens proteins. A healthy diet rich in sources of antioxidants, including citrus fruits, sweet potatoes, carrots,green leafy vegetables, and/or vitamin supplements may be helpful.