Cataracts are a common age-related vision problem. About 22 million Americans age 40 and older have cataracts, and the older a person gets the greater the risk for developing cataracts. Women are more likely to develop cataracts than men, and African-Americans and Hispanic Americans are at particularly high risk.
In addition to age, other factors may increase the risk of cataract development. These include:
- Overexposure to sunlight
- Certain medications, such as steroids
During the early stages, cataracts may have little effect on vision. Symptoms vary due to the location of the cataract in the eye (nuclear, cortical, or posterior subcapsular). Depending on the type and extent of the cataract, patients may experience the following symptoms:
- Cloudy vision
- Double or blurry vision
- Glare and sensitivity to bright lights
- Colors appear faded
- Difficulty reading due to reduced black-white contrast
- Difficulty driving at night
Cataracts never go away on their own, but some stop progressing after a certain point. But if cataracts continue to grow and progress, they can cause blindness if left untreated. Fortunately, cataracts can almost always be successfully treated with surgery. Millions of cataract operations are performed each year in the United States, and there is a very low risk for complications. However, before opting for surgery, patients need to consider on an individual basis how severely a cataract interferes with their quality of life. Cataract surgery is rarely an emergency, so patients have time to consult with their doctors and carefully consider the risks and benefits of surgery.
Cataract Removal Surgery
Surgery involves removing the cataract and replacing the abnormal lens with a permanent implant called an intraocular lens (IOL). The operation takes less than 1 hour and is performed on an outpatient basis. The procedure is generally painless and most patients remain awake, but sedated, during it. If you have cataracts in both eyes, doctors recommend waiting at least 1 month between surgeries.
A cataract is an opacity, or clouding, of the lens of the eye.
The likelihood of developing cataracts increases with age. Cataracts typically occur in the following way:
- The lens is an elliptical structure that sits behind the pupil and is normally transparent. The function of the lens is to focus light rays into images on the retina (the light-sensitive tissue at the back of the eye).
- In young people, the lens is elastic and changes shape easily, allowing the eyes to focus clearly on both near and distant objects.
- As people reach their mid-40s, biochemical changes occur in the proteins within the lens, causing them to harden and lose elasticity. This causes a number of vision problems. For example, loss of elasticity causes presbyopia, or far-sightedness, requiring reading glasses in almost everyone as they age.
- In some people, the proteins in the lens, notably those called alpha crystallins, may clump together, forming cloudy (opaque) areas called cataracts. They usually develop slowly over several years and are related to aging. In some cases, depending on the cause of the cataracts, loss of vision progresses rapidly.
- Depending on how dense they are and where they are located, cataracts can block the passage of light through the lens and interfere with the formation of images on the retina, causing vision to become cloudy.
Cataracts can form in any of three parts of the lens and are named by their location.
- Nuclear cataracts. These form in the nucleus (the inner core) of the lens. This is the most common type of cataract associated with the aging process.
- Cortical cataracts. These form in the cortex (the outer section of the lens).
- Posterior subcapsular cataracts. These form toward the back of a cellophane-like capsule that surrounds the lens. They are more frequent in people with diabetes, those who are overweight, or those taking steroids.
Although older age is the primary risk factor for cataracts, researchers are still not certain about the exact biologic mechanisms that tie cataracts to aging.Oxygen-Free Radicals (Oxidants) and Glutathione
Particles called oxygen-free radicals may be a major factor in the development of cataracts. They cause harm in the following way:
- Oxygen-free radicals (also called oxidants) are molecules produced by natural chemical processes in the body. Toxins, smoking, ultraviolet radiation, infections, and many other factors can create reactions that produce excessive amounts of oxygen-free radicals. When oxidants are overproduced, these chemicals can be very harmful to cells throughout the body.
- Cataract formation is one of many damaging changes that can occur from overproduction of oxidants, possibly in combination with deficiencies of an important protective anti-oxidant called glutathione.
- Glutathione occurs in high levels in the eye and helps fight back against free radicals. One theory is that in the aging eye, barriers develop that prevent glutathione and other protective antioxidants from reaching the nucleus in the lens, thus making it vulnerable to oxidation.
Sunlight and Ultraviolet Radiation. Sunlight consists of ultraviolet (referred to as UVA or UVB) radiation, which penetrates the layers of the skin. Both UVA and UVB have damaging properties that can promote cataracts. The eyes are protected from the sun by eyelids and the structure of the face (overhanging brows, prominent cheekbones, and the nose). Long-term exposure to sunlight, however, can overcome these defenses.
- UVB radiation produces the shorter wavelength, and primarily affects the outer skin layers. It is the main cause of sunburn. It is also the type of UV radiation primarily responsible for cataracts. Long-term exposure to even low levels of UVB radiation can eventually cause changes in the lens, including pigment changes, which contribute to cataract development. (UVB also appears to play a role in macular degeneration, an age-related disorder of the retina.) Some scientists suggest that global warming and ozone depletion may increase people’s exposure to UVB, leading to a greater incidence of cataracts.
- UVA radiation is composed of longer wavelengths. They penetrate more deeply and efficiently into the inner skin layers and are responsible for tanning. The main damaging effect of UVA appears to be the promotion of the release of oxidants.
Radiation Treatments. Cataracts are common side effects of total body radiation treatments, which are administered for certain cancers.
Electromagnetic Waves. Questions have been raised about the hazards of low-level radiation from computer screens. To date, no study has demonstrated an association between cataract development and video display terminals. It is a good idea, in any case, to sit at least a foot away from the front of a screen.Medications
Corticosteroids. Long-term use of oral steroids is a well-known cause of cataracts. Studies have been conflicting, however, over whether inhaled and nasal-spray steroids increase the risk for cataracts. Information on cataract risk from inhaled steroids is important because they are commonly used for treatment of asthma and allergies.
Other Medications Associated with Cataracts.
- Psoralens, a class of drugs used along with light therapy to treat skin disorders, such as psoriasis
- Antipsychotic medications such as chlorpromazine (Thorazine)
- Glaucoma medications
Many others drugs have been weakly associated with cataracts, including allopurinol, tamoxifen, amiodarone, tricyclic antidepressants, potassium-sparing diuretics (but not other diuretics), thyroid hormone, tetracyclines, sulfamidase, and mepacrine. Statin drugs (used for managing cholesterol) may possibly reduce the risk for nuclear cataracts.Causes of Cataracts in Children
Rarely, about 1 in every 10,000 births, a baby is born with cataracts (called congenital cataracts).
- Inherited disorders are often involved in the development of congenital cataracts in children. Such cataracts are most often due to inborn abnormalities in the structure or shape of the lens, including its capsule. Certain types of genetic factors may play a role.
- Infection during pregnancy can lead to cataracts.
- Pregnant women who abuse alcohol or drugs increase the risk for cataracts (along with other more serious birth defects) in their infants.
Aging is the primary risk factor for cataracts, but other factors are also involved.Age
Nearly everyone who lives long enough will develop cataracts to some extent. Some people develop cataracts during their middle-aged years (40s and 50s), but these cataracts tend to be very small. It is after age 60 that cataracts are most likely to affect vision. Nearly half of people age 75 and older have cataracts.Gender
Women face a higher risk than men.Family History
Cataracts tend to run in families.Race and Ethnicity
African-Americans have nearly twice the risk of developing cataracts as Caucasians. This difference may be because African-Americans are also more likely to have diabetes, which is a risk factor for cataracts. African-Americans are much more likely to become blind from cataracts and glaucoma than Caucasians, mostly due to lack of medical care.
Hispanic Americans are also at increased risk for cataracts. In fact, cataracts are the leading cause of visual impairment among Hispanics.Glaucoma and Other Eye Conditions
Glaucoma. Glaucoma and its treatments, including certain drugs (notably miotics) and filtering surgery, pose a high risk for cataracts. The glaucoma drugs that can increase risk for cataracts include demecarium (Humorsol), isoflurophate (Floropryl), and echothiophate (Phospholine).
Myopia. People who are nearsighted (myopic) are at increased risk of developing cataracts.
Uveitis. Uveitis is chronic inflammation in the eye, which is often caused by an autoimmune disease or response. Often the cause is unknown. It is a rare condition that carries a high risk for cataracts.
Other Eye Conditions. Physical injuries to the eye (such as a hard blow, cut, or puncture) or eye inflammation can also increase risk. Previous intraocular eye surgery increases cataract risk.Other Medical Conditions
Diabetes. People with diabetes type 1 or 2 are at very high risk for cataracts and are much more likely to develop them at a younger age. They also have a higher risk for nuclear cataracts than nondiabetics. Cataract development is significantly related to high levels of blood sugar (hyperglycemia). Obesity, which is associated with diabetes type 2, may also be a risk factor for cataracts.
Autoimmune Diseases and Conditions Requiring Steroid Use. Medical conditions requiring long-term use of oral corticosteroids (commonly called steroids) pose a particularly high risk. Many of these medical conditions are autoimmune diseases, including rheumatoid arthritis, psoriasis, multiple sclerosis, systemic lupus erythematosus, Behcet's disease, and others.Overexposure to Sunlight
Exposure to even low-level UVB radiation from sunlight increases the risk for cataracts, especially nuclear cataracts. The risk may be highest among those who have significant sun exposure at a young age. People whose jobs expose them to sunlight for prolonged periods are also at increased risk.Smoking and Alcohol Use
Smoking. Smoking a pack a day of cigarettes doubles the risk of developing cataracts. Smokers are at particular risk for cataracts located in the nuclear portion of the lens, which limit vision more severely than cataracts in other sites.
Alcohol. Chronic heavy drinkers are at high risk for a number of eye disorders, including cataracts.Environmental Factors
Long-term environmental lead exposure may increase the risk of developing cataracts. Gold and copper accumulation may also cause cataracts. Prolonged exposure to ionizing radiation (such as x-rays) can increase cataract risk.
Some cataracts stop progressing after a certain point but they never go away on their own. If extensive and progressive cataracts are left untreated they can cause blindness. In fact, cataracts are the leading cause of blindness among adults age 55 and older.
Fortunately, cataracts can nearly always be successfully removed with surgery. However, surgery is unavailable in certain parts of the world, leaving millions at risk for vision loss. Even in the U.S., where surgery has greatly reduced the risk of blindness, tens of thousands still lose their sight and millions more have poor vision because of cataracts.Effect on Daily Functioning
Some people who have small cataracts can see well enough around the clouded areas to live normally. Extensive cataracts, however, can affect people’s abilities to earn a living, read, drive, or live independently and can interfere greatly with daily activities.
Although cataracts are not completely preventable, their occurrence can be delayed. Quitting smoking, avoiding overexposure to sunlight, avoiding excessive amounts of alcohol, and eating plenty of fresh fruits and vegetables are important protective measures. There is no proof that using eye drops or ointments or performing eye exercises can prevent the onset of cataracts.Avoiding Ultraviolet Radiation
The simplest and most effective way to protect against ultraviolet (UV) radiation is to stay out of the sun. Wear a hat and cover-up outside, especially when the sun is most intense (10 a.m. - 3 p.m.). A wide-brimmed hat can significantly reduce eye exposure to UVB radiation. Because the sun's rays are highly reflective, sitting in the shade or under an umbrella by itself does not guarantee protection.
Note: Moderate sun exposure provides an important source of vitamin D, which is essential for healthy bones and other health factors. Fortunately, people who protect themselves from the ultraviolet radiation in sunlight can get the vitamins they need from supplements.
Sunglasses. Protective sunglasses do not have to be expensive. But it is important to select sunglasses whose product labels state they block at least 99 percent of UVB rays and 95 percent of UVA rays.
Polarized and mirror-coated lenses do not offer any protection against UV radiation. It is not clear if blue light-blocking lenses, which are usually amber in color, provide UV protection.Diet and Nutrition
Scientists are not certain if nutrition plays a significant role in cataract development. Dark colored (green, red, purple, and yellow) fruits and vegetables usually have high levels of important plant chemicals (phytochemicals) and may be associated with a lower risk for cataracts.
In analyzing nutrients, researchers have focused on antioxidants and carotenids. Studies have not demonstrated that antioxidant vitamin supplements (such as vitamins C and E) help prevent cataracts. Still, fruits and vegetables containing these vitamins are important for overall good health.
Lutein and zeaxanthin are the two carotenids that have been most studied for cataract prevention. They are xanthophylis compounds, which are a particular type of carotenid. Lutein and zeaxanthin are found in the lenses of the eyes. Some evidence indicates that xanthophyll-rich foods (such as dark green leafy vegetables) may help slow the aging process in the eye and protect against cataracts. However, there is not enough evidence to suggest that taking supplements that contain these carotenoids lowers the risk for cataract formation.
During the early stages, cataracts have little effect on vision. As the cataract progresses, symptoms may include:
- Cloudy vision, double vision, or both may be the first signs.
- Images may take on a yellowish tint as color vibrancy diminishes.
- Reading may become difficult over time because of a reduced contrast between letters and their background.
- Sensitivity to bright lights may make it difficult or impossible to drive at night because of glare from the headlights of oncoming cars. (People with diffuse cataracts in the rear walls of their lenses are particularly prone to glare sensitivity because bright light tends to scatter in their lenses.)
- In very advanced cases, the pupil, which is normally black, looks milky or yellowish. The patient's vision is reduced to being able only to distinguish light from dark.
Symptoms may vary depending on the part of the lens that is affected.
Nuclear Cataracts. Cataracts of the lens nucleus are most commonly associated with aging. Symptoms include:
- Hazy distance vision and increasing glare.
- Progressive nearsightedness and the need for frequent changes in eyeglass prescriptions. This effect may even temporarily counteract age-related farsightedness and provide a temporary improvement in overall vision in some people. The improvement fades when the cataract advances sufficiently to overwhelm the inherent farsightedness. Eventually, as the cataract grows worse, stronger glasses can no longer correct the patient's vision.
Cortical Cataracts. Cortical cataracts usually start on the outside of the cortex (the outer area of the lens).
- They have very little initial effect on vision.
- Glare can develop as these cataracts increase and approach the center of the lens.
- Problems with distance vision, contrast sensitivity, and clarity may occur as the cataracts progress further.
Posterior Subcapsular Cataracts. Posterior subcapsular cataracts typically start near the center of the back part of the capsule surrounding the lens. These cataracts often advance rapidly. For many patients, major impairment of eyesight, including near-vision problems and glare, develops within several months.
Either an ophthalmologist or an optometrist can examine patients for cataracts, but only ophthalmologists are qualified to treat cataracts.
- An ophthalmologist is a medical doctor (M.D.) who specializes in the medical and surgical care of the eye.
- An optometrist is a doctor of optometry (O.D.) who practices eye care and prescribes corrective lenses but does not perform surgery.
The eye professional can observe cloudy areas on the lenses with a physical examination, even before the cataracts begin to interfere with vision. Cameras can measure the cataract density. Various vision tests are also performed.
Snellen Eye Chart. To determine how clearly a person can actually see, the Snellen eye chart is used, with rows of letters decreasing in size:
- From a specified distance, usually 20 feet, a person reads the letters using one eye at a time.
- If a person can read down to the small letters on the line marked 20 feet, then vision is 20/20 (normal vision).
- If a person can read only down through the line marked 40 feet, vision is 20/40; that is, from 20 feet the patient can read what someone with normal vision can read from 40 feet.
- If the large letters on the line marked 200 feet cannot be read with the better eye, even with glasses, the patient is considered legally blind.
Other Tests. A number of other tests are used to diagnose cataracts or to determine if surgery is needed.
- A chart similar to the Snellen chart, which has the same size letters, but in different contrasts with background, is used to test contrast sensitivity.
- Glare sensitivity is tested by having the patient read a chart twice, with and without bright lights.
- Tests of macular function, which evaluate the eye's acute vision center, can help the ophthalmologist determine the expected improvement from surgery.
- The corneal endothelium, a layer of cells lining the cornea, is sensitive to surgical trauma and should be evaluated before any intraocular operation.
- Patients with other eye disorders may need other pre-operative tests.
Although eye tests help confirm a diagnosis of cataracts, results do not always reflect the quality of life and how effectively people function at home:
- Some people with cataracts perform poorly on the tests yet have no trouble with daily function.
- Others perform well on the tests but find that their eyesight is bad enough to interfere with ordinary activities, such as driving.
Although surgery is the only remedy for cataracts, it is almost never an emergency. Most cataracts cause no problem other than reducing a person's ability to see, so there is no harm in delaying surgery.
The following measures may manage early cataracts:
- Stronger eyeglasses or contact lenses
- Use of a magnifying glass during reading
- Strong lighting
- Medication that dilates the pupil. (This may help some people with capsular cataracts, although glare can be a problem with this treatment.)
Progression of Cataracts. Patients and their families usually have plenty of time to carefully consider options and discuss them with an ophthalmologist. There is no constant rate at which cataracts progress:
- Some cataracts develop to a certain point and then stop.
- Even if a cataract does progress, it may be years before it interferes with vision.
- It is very rare for people