Cataracts

Cataracts are a common age-related vision problem. About 20.5 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:

• Diabetes
• Smoking
• Over-exposure to sunlight

Symptoms

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

Treatment

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 usually always be successfully removed with surgery. Millions of cataract surgeries 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 during it. If you have cataracts in both eyes, doctors recommend waiting at least 1 month between surgeries.

Introduction

A cataract is an opacity, or clouding, of the lens of the eye.

The lens of an eye is normally clear. If the lens becomes cloudy or is opacified, it is called a cataract.

The prevalence of cataracts increases dramatically with age. It typically occurs 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 also 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.

Click the icon to see an image of eye anatomy.

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 variety 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, who are overweight, or those taking steroids.

Causes

Although older age is the primary risk factor for cataracts, experts are still not certain about the exact biologic mechanisms that tie cataracts to aging.

Oxygen-Free Radicals (Oxidants) and Glutathione

Researchers have been focusing on particles called oxygen-free radicals as 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 these oxygen-free radicals.
• Oxidants are missing an electron, so they are unstable and tend to chemically bind with other molecules in the body. When oxidants are overproduced, these chemical reactions can be very harmful to nearly any type of cell in the body. At times these reactions can even affect genetic material in cells.
• Cataract formation is one of many destructive changes that can occur with overproduction of oxidants, possibly in concert with deficiencies of an important protective anti-oxidant called glutathione.
• Glutathione occurs in high levels in the eye and helps clean up these free radicals. One theory posits that in the aging eye, barriers develop that prevent glutathione and other protective antioxidants from reaching the nucleus in the lens, thus making if vulnerable to oxidation.

Radiation and Electromagnetic Waves

Sunlight and Ultraviolet Radiation. Sunlight consists of ultraviolet (referred to as UVA or UVB) radiation, which penetrates the layers of the skin. Both have destructive 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 primary cause of sunburn. It is also the 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 be responsible for macular degeneration, an age-related disorder of the retina.) Some scientists suggest that global warming and ozone depletion may increase peoples 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.