A cataract is a cloudy area in the normally clear lens inside the eye. The cloudy area worsens as protein ﬁbers in the lens clump together, preventing light rays from passing through the lens and focusing on the retina, the light-sensitive membrane that lines the back of the eye. Cataracts usually develop very gradu- ally, and early changes in the lens of the eye may go unnoticed. As the cataract continues to develop, symptoms begin to appear. The person may have blurred vision in one eye. Bothersome glare caused by bright sunlight or vehicle head- lights is common. The person also may have poor night vision. Colors appear to be less bright. The person may experience increased nearsightedness that requires frequent changes in his or her eyeglass prescription. The person also may ﬁnd it more difﬁcult to see well enough to read and perform other daily tasks.
Cataracts in adults can be classiﬁed into three general types, depending on their location in the lens. The most common type is called a nuclear cataract or an age-related cataract and occurs in the center of the lens. The term “age- related” is somewhat misleading because people can have this type of cataract in their 40s and 50s. During middle age, most cataracts are mild and do not affect
vision. After age 60, however, cataracts more commonly begin to interfere with vision. The second type of cataract is a cortical cataract, which starts as a wedge- shaped spoke at the outer layer of the lens. The spoke descends from the outer layer into the center, where it obstructs the transmission of light. This type of cataract can develop in people who have diabetes. The third type of cataract is called a subcapsular cataract. It starts as a small clouding at the back of the lens and develops slowly.
The exact cause of cataracts is unknown, although doctors have identiﬁed cer- tain factors that may be involved in their development. Research has shown that people who live at high altitudes or who spend much time in the sun develop cataracts earlier than other people. Many ophthalmologists now advise people to wear sunglasses that protect against both ultraviolet A and B (UV-A and UV-B) rays and to wear a wide-brimmed hat to protect the eyes against sun expo- sure whenever they go outdoors. People who have diabetes also seem to have an increased risk of developing cataracts, as do those who take certain medications, such as corticosteroids. If you have any of these risk factors, talk to your doctor about your chances of developing cataracts.
To diagnose cataracts, an ophthalmologist will perform a thorough eye exam- ination. He or she will dilate your pupils with eyedrops and will examine the inside of your eyes with a slit lamp microscope (a viewing instrument with a bright light and magnifying lenses) to detect any clouding of the lens. If a cataract is present, the doctor will determine the type, size, and location of the cataract.
At present there are no eyedrops or other medications that will eliminate cataracts. At ﬁrst, your vision may be improved with prescription eyeglasses, bifocals, a magnifying glass for reading, or better lighting at home or at work. Once your vision becomes so poor that it affects your ability to function inde- pendently, you will probably need to undergo surgery to have the cataracts removed. However, you may not need surgery for many years; some people with cataracts never need surgery.
During cataract surgery the surgeon removes the clouded lens and usually replaces it with an artiﬁcial lens. Cataract surgery is one of the most common operations performed in the United States and also is one of the most successful. Good vision is restored in more than 90 percent of people who have cataract sur- gery. After surgery you will probably have to use eyedrops or wear protective eyeglasses for a time. Your vision may not become fully restored until a few weeks or months after surgery. Most people with a lens implant will need to wear bifocals.
In some cases the posterior capsule (the membrane at the back of the lens) may become cloudy months or even years after cataract surgery, causing blurred vision. This condition can be corrected with a surgical procedure that uses a laser (a highly concentrated, powerful beam of light). The procedure is
brief and painless and can be performed in the doctor’s ofﬁce or in an outpatient facility.
If you are over age 60, the best way to protect your vision and to check for cataracts is to have your eyes examined by an ophthalmologist at least every 2 years. The examination should include dilation of the pupil so the doctor can see the lens and the back of the eyes. If a cataract is detected, your ophthalmologist will work with you to decide on the best course of treatment and will explain the risks and the beneﬁts of cataract surgery.
Diabetic retinopathy is an eye disorder caused by diabetes (see page 365), a chronic disease that can damage blood vessels, including those in the eye. A leading cause of blindness in adults in the United States, diabetic retinopathy is caused by changes in the blood vessels of the retina, the light-sensitive mem- brane that lines the back of the eye. In some people, the blood vessels leak ﬂuid. In others, abnormal new blood vessels grow on the surface of the retina. These abnormal blood vessels can bleed and leak into the vitreous humor (the jellylike substance that ﬁlls the center of the eye), preventing light from passing through to the retina. The abnormal blood vessels and bleeding also can produce scar tis- sue that pulls the retina away from the back of the eye, causing a detached retina. Anyone with diabetes can develop diabetic retinopathy, and the longer a person has diabetes, the more likely he or she is to develop this disorder. Nearly half of all people with diabetes will develop diabetic retinopathy.
There may be no obvious symptoms in the early stages of the disease, but some people with diabetic retinopathy experience blurred vision when the macula (the part of the retina that provides sharp central vision) swells because of the leaking ﬂuid. Abnormal blood vessels that have grown on the surface of the retina can cause symptoms such as blurred vision, seeing spots, vision that alternates between being normal and diminished, pain in the eyes, and sudden loss of vision. If you experience any of these symptoms, contact your ophthal- mologist immediately. In some cases, vision may not become impaired until the disease is severe. That is why regular (at least yearly, or more often if recom- mended by your physician) eye examinations performed by an ophthalmologist are so important for people with diabetes.
During the eye examination, the ophthalmologist will dilate your pupils with eyedrops and then examine your retina using an ophthalmoscope (a handheld viewing instrument that projects a very bright light onto the back of the eye). He or she will look for leaking ﬂuid, abnormal bleeding, or new blood vessel growth on the retina. Early detection and treatment of diabetic retinopathy go a long way toward preventing vision loss and blindness and minimizing potential vision problems.
The best way to prevent diabetic retinopathy and to slow its progression is to consistently control the level of glucose in your blood (see page 368) through diet, exercise, medication, and insulin, if necessary. It also is important to keep your blood pressure within the normal range (see page 219). In some cases the ophthalmologist may recommend laser surgery in which a highly concentrated beam of light is directed onto the retina either to shrink abnormal blood vessels or to seal leaking blood vessels. This procedure can be performed in the doctor’s ofﬁce or in an outpatient facility. Laser surgery can reduce the risk of severe vision loss from diabetic retinopathy, but it may not restore vision that has already been lost.
A type of microsurgery (delicate surgery performed under a microscope) called vitrectomy may be used for advanced cases of diabetic retinopathy, in which the vitreous humor has become ﬁlled with blood. In this procedure the vitreous humor is removed and replaced with a clear solution. Vitrectomy may take several hours to complete and is performed in an operating room using either local or general anesthesia. The procedure can cause discomfort. Recovery time varies, depending on the extent of the problem.
Surgery to reattach the retina may be needed if scar tissue causes the retina to become detached from the back of the eye. The procedure is performed using either local or general anesthesia and may be combined with laser surgery or vitrectomy. Surgery may take several hours to complete and is performed in an operating room. The procedure can cause discomfort.
People who have diabetes are also at risk for other eye diseases. They are twice as likely to develop a cataract (see page 390) as people without diabetes, and the cataracts tend to develop at an earlier age. Glaucoma (see page 388) also occurs in people with diabetes twice as often as in other adults. The longer you have diabetes, the higher your risk of developing glaucoma.
The part of the retina (the light-sensitive membrane that lines the back of the eye) that provides sharp sight in the center of the ﬁeld of vision is called the macula. You need this sharp central vision to see ﬁne details. It is essential for driving, reading, and recognizing faces. As you age, the tissue of the macula can become damaged, leading to a loss of central vision. Age-related macular degen- eration is the leading cause of blindness in the United States.
There are two general types of macular degeneration: dry and wet. The dry form accounts for about 90 percent of all cases of the disorder. In this form, the macula slowly thins until vision becomes dimmed. Although only about 10 per- cent of all people with macular degeneration have the wet form, they are at much higher risk of losing their sharp central vision than are those with the dry form. New blood vessels grow under the retina in the wet form of the disease. These
blood vessels bleed and leak ﬂuid, creating a large blind spot in the center of the ﬁeld of vision.
The greatest risk factor for macular degeneration is age. Although symptoms can appear when a person is in his or her 40s or 50s, they usually occur in peo- ple over age 60. Women tend to be at greater risk than men, and whites have a higher risk than people of other races. Smoking also appears to increase the like- lihood of developing macular degeneration.
Neither form of macular degeneration causes pain. The most common early symptom is blurred vision. As fewer cells in the macula are able to function, affected people are less able to see details—for example, in faces or on printed pages. The blurred vision may lessen in more brightly lit areas, but once the light-sensing cells degenerate, a small but growing blind spot appears in the mid- dle of the ﬁeld of vision. Another symptom is that objects in straight lines, such as telephone poles or sentences on a page, appear crooked. This phenomenon can occur because ﬂuid from the leaking blood vessels collects and lifts the mac- ula, distorting vision.
To diagnose macular degeneration, an ophthalmologist will use eyedrops to dilate your pupils and an ophthalmoscope (a handheld viewing instrument that projects a very bright light onto the back of the eye) to view the retina. The doc- tor also may ask you to look at a pattern called an Amsler grid, which looks like a checkerboard. If your central vision is affected, the lines of the grid will appear wavy or distorted.
Currently there is no proven treatment for dry macular degeneration. Some doctors believe that taking antioxidant vitamins (see page 9), zinc supplements, or lutein (an antioxidant found in plants such as spinach, kale, and collard greens) may be helpful in slowing the progression of the disease. A number of low-vision aids, such as magnifying glasses or bright lights, can help affected people continue to participate in activities they enjoy and to lead independent lives.
Some cases of wet macular degeneration can be treated with laser surgery, in which a highly concentrated beam of light is used to destroy the new blood ves- sels under the retina. Laser surgery is less successful when the abnormal blood vessels have grown beneath the center of the macula. Laser surgery is usually performed in a doctor’s ofﬁce or in an outpatient facility, and the person is allowed to go home the same day.
Color Vision Deficiency
Color vision deﬁciency (color blindness) refers to abnormal color vision that causes a person to see colors differently than others see them or that causes prob- lems distinguishing certain colors. The deﬁciency may range from difﬁculty telling the difference between shades of the same color to total inability to see
any colors at all. Most people with this problem have a mild deﬁciency and have difﬁculty distinguishing shades of red and green.
Color vision deﬁciency is usually an inherited disorder. It is predominant in men, and about 8 percent of all males are affected, although women can carry the gene for defective color vision and pass it to their children. In people with color vision deﬁciency, receptor cells for color in the retina (the light-sensitive mem- brane that lines the back of the eye) malfunction, sending incorrect information about color to the brain. The severity of the disorder varies from person to per- son. Color vision deﬁciency is diagnosed according to the person’s symptoms and the results of color vision testing.
Some people have defective color vision that is not inherited. Aging can cause the lens of the eye to darken, affecting a person’s ability to differentiate colors. Certain drugs and eye diseases also can disturb normal color vision.
There is no cure for inherited color vision deﬁciency, but affected people can take steps to counteract the problem. Some people learn to compensate by devel- oping their own methods of distinguishing different colors—for example, by brightness or location. Tinted prescription eyeglasses may help some people who have red-green color vision deﬁciency.
If you have a family history of color vision deﬁciency and work in an occupa- tion that requires distinguishing colors, or if you are having trouble identifying colors, see an ophthalmologist to be tested for color vision deﬁciency. He or she can recommend steps you can take to compensate for the problem.