Overview of Cataracts
A cataract is the clouding or opacity that develops in the eye's lens. The crystalline lens is comprised primarily of protein and water. Normally, the protein is bonded in a way that allows light to pass through it. A cataract forms when bonding changes and protein molecules clump together. Eventually, these clumps cloud the lens and block light. If left untreated, cataracts may eventually cause blindness.
Incidence & Prevalence of Cataracts
In the United States, about 50 percent of people between the ages 65 and 74, and 70 percent 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.
Types of Cataracts
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.
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.
Cortical cataracts form in the lens cortex (peripheral area). They eventually extend like spokes on a wheel into the nucleus of the lens.
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.
Causes & Risk Factors for Cataracts
Aging is the primary risk factor for cataracts. Other factors determine overall risk for and severity of the condition. When cataracts occur in younger patients, they are usually caused by a chronic medical condition, eye trauma, or prescription drug.
Medical conditions such as diabetes, myotonic dystrophy, or Wilson's disease increase the risk for cataracts, regardless of age. Slowly progressing cortical cataracts are common in diabetics. Diabetic patients or those who take high doses of steroids are more at risk for subcapsular cataracts.
Certain drugs can stimulate cataract development. These include the following:
- Amiodarone (Cordarone), heart medication
- Chlorpromazine (Largactil), sedative
- Corticosteroids (e.g., prednisone), used to treat inflammation in many acute and chronic illnesses
- Lovastatin (Mevacor), cholesterol-lowering drug
- Phenytoin (Dilantin), antiseizure drug used to treat epilepsy
Fetal exposure to infection, radiation, steroids, alcohol, and other substances of abuse during pregnancy are risk factors for congenital cataracts.
Smoking and alcohol abuse increase the risk for cataracts. Individuals who smoke 20 or more cigarettes a day have twice the risk of nonsmokers for developing cataracts. Long-term alcohol abuse leads to vitamin deficiencies that may lead to development of the condition.
Deficiencies in vitamins C and E, selenium, beta carotene, and lycopene may be linked to cataract development. These antioxidants protect the body from free radicals that cause damage to cell walls and other cell structures, as well as the genetic material within cells.
African Americans may be at higher risk for cataracts, possibly because of this group's higher risk for some chronic conditions (e.g., diabetes) that increase the risk for cataracts.
Prolonged exposure to sunlight, specifically ultraviolet B (UVB), is a risk factor for cataracts. The longer the exposure, the greater the risk. However, even a low level of exposure increases risk.
An eye injury may increase the risk for a cataract.
Eye disease (e.g., uveitis) or infection can lead to cataracts. A tumor can also cause changes that may lead to the development of cataracts.
Signs & Symptoms of Cataracts
Symptoms depend on the cataract's location in the lens and the amount of clouding. Cataracts are painless and often progress slowly, so many years may pass before a patient experiences symptoms. If only one eye develops a cataract, the patient may never experience symptoms, as long as sight in the other eye remains stable.
Common symptoms of cataracts include:
- Blurry vision
- Colors appear faded
- Frequent changes in prescription eyeglasses or contacts
- Poor night vision
- Seeing a halo around lights
- Sensitivity to bright sunlight or headlight glare at night
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.