A cataract is a clouding (opacity) of the lens of the eye that causes a progressive, painless loss of vision.
Cataracts are the leading cause of blindness worldwide. Cataracts are common in the United States, where they affect mostly older adults. Almost one in five people between the ages of 65 and 74 develops cataracts severe enough to reduce vision, and almost one in two people older than 75 has them. Fortunately, people in the United States can often have their cataracts treated before they cause blindness.
Cataracts usually occur with aging or develop without any apparent cause. However, other factors include the following:
People who have had a cataract in one eye are more likely to develop one later in the other eye. Sometimes cataracts can develop in both eyes at the same time. Babies can be born with them (congenital cataracts—see see Other Birth Defects), and children can also develop cataracts, usually as a result of injury or illness.
Because all light entering the eye passes through the lens, clouding of the lens can block and scatter light and cause poor vision. The first symptom of a cataract may be blurred vision. Sometimes, the first symptom is seeing halos and starbursts around lights (glare). Less commonly, double vision (also called ghost images) is an early symptom. A person may also notice that colors seem more yellow and less vibrant. Reading may become more difficult because of a worsening ability to distinguish the contrast between the light and dark of printed letters on a page.
How much vision is changed by a cataract depends on the intensity of light entering the eye and on the location of the cataract.
With a cataract near the back of the lens (posterior subcapsular cataract), sharpness of vision (visual acuity) is worse when the pupil constricts (for example, in bright light or during reading). Posterior subcapsular cataracts are also more likely to cause loss of contrast, as well as halos and starbursts (glare) from bright lights or car headlights while driving at night. People with cataracts who take drugs that constrict their pupils (certain glaucoma eye drops, for example) may also have greater vision loss.
With a cataract in the center (inside) of the lens (nuclear cataract), distance vision worsens. However, near vision may at first improve because the cataract acts as a stronger lens, thus refocusing light. Older people who have needed eyeglasses to see things that are close since their mid-40s may discover that they can once again see things that are close without eyeglasses, a phenomenon often described as gaining second sight. Unfortunately, a nuclear cataract eventually blocks and blurs light entering the eye and impairs vision.
Although cataracts almost never cause pain, they very rarely swell and increase the pressure in the eye (glaucoma), which can be painful.
A doctor can usually detect a cataract while examining the eye with an ophthalmoscope (a hand-held light with a magnifying lens that can shine into the back of the eye). A doctor can identify the exact location of the cataract and the extent to which it blocks light by using an instrument called a slit lamp (an instrument that enables a doctor to examine the eye under high magnification). The slit lamp allows examination of the lens and other parts of the eye in more detail.
There are several things people can do to try to prevent cataracts. Consistent use of eyeglasses or sunglasses with a coating to filter ultraviolet (UV) light protects the eyes from bright sunlight and may help. Not smoking and reducing consumption of alcohol are useful and have other health advantages. People with diabetes should work with their doctor to be sure the level of sugar in their blood is well controlled. A diet high in vitamin C, vitamin A, and substances known as carotenoids (contained in vegetables such as spinach and kale) may protect against cataracts. Estrogen use by women after menopause may also be protective, but estrogen should not be used solely for this purpose. Finally, people who are taking corticosteroids for extended periods might discuss with their doctor the possibility of using a different drug.
Until vision is significantly impaired, eyeglasses and contact lenses may improve a person's vision. Wearing sunglasses in bright light and using lamps that provide over-the-shoulder lighting may decrease glare and aid vision. Occasionally, drops that keep the pupil dilated may be used to help vision if the cataract is small and located in the back of the lens.
The only treatment that provides a cure for cataracts is surgery. There are no eye drops or drugs that will make cataracts go away. Very rarely, cataracts cause changes (such as swelling of the cataract or glaucoma) that lead doctors to recommend the cataract be removed quickly. However, most times people should have surgery only when their vision is so impaired by cataracts that they feel unsafe, uncomfortable, or unable to perform daily tasks. There is no advantage to having cataracts removed before then.
Cataract surgery can be done on a person of any age and is generally safe even for people with illnesses such as heart disease and diabetes. Usually, the doctor makes a small incision in the eye and removes the cataract by breaking it up with ultrasound and taking the pieces out of the lens capsule (phacoemulsification). When all the cataract pieces have been removed, the surgeon usually places a plastic or silicone lens (intraocular lens) in the lens capsule. However, the intraocular lens cannot always be safely placed. When lens placement is not possible, people must wear thick eyeglasses or contact lenses after the cataract has been removed.
Surgery to remove cataracts is almost always done using a local anesthetic (an injection or eye drops) to numb the eye surface. People usually receive a sedative also. Rarely, children or adults who cannot hold still during surgery require general anesthesia. The procedure normally takes about 30 minutes, and the person can go home the same day. No sutures are usually needed because the incision into the eye is small and seals itself.
People should make arrangements in advance to get extra help at home for a few days after surgery because activity may be restricted (for example, bending over and heavy lifting may be prohibited), and vision changes, such as blurred vision and discomfort with bright light, may occur for a short time after surgery. For a few weeks after surgery, corticosteroid eye drops and antibiotic eye drops are used to prevent infection, reduce inflammation, and promote healing. People are given eyeglasses or a plastic shield to wear while sleeping to protect the eye from injury until healing is complete, usually a few weeks. Rubbing the eye is avoided. People visit the doctor the day after surgery and then typically one week and one month later. If a person has cataracts in both eyes, many doctors wait several months after the first eye has healed to remove a cataract from the other eye.
Many people notice improved distance vision within a few weeks after cataract surgery. Almost everyone will need eyeglasses for reading, and some people will need eyeglasses to obtain the best possible distance vision as well. Newer intraocular lenses with multiple focusing powers (multi-focal lenses) may allow a person to have good near and distance vision without needing glasses, although some people may lose contrast and experience starbursts and halos at night with these lenses. The doctor makes calculations before the surgery to decide how powerful the artificial lens should be. Thus, it is possible to go from wearing very thick eyeglasses before the surgery to wearing much thinner eyeglasses after it. Some people no longer need eyeglasses or need them for only certain things, such as driving at night, reading in dim light, or for mid-range vision, such as viewing a computer monitor.
Complications after cataract surgery are rare. A person may develop an infection or serious bleeding in the eye, which can lead to a loss of vision. Eye pressure may become too high, which if left untreated, leads to glaucoma, or the implant can become displaced. The back of the eye (retina) can become swollen or detached (see see Detachment of the Retina). Rarely, people with retinal disorders, such as diabetic retinopathy, may notice their vision worsen after the operation. Proper follow-up with the doctor can lead to early detection and treatment of these unusual complications.
In some people, the tissue (capsule) left behind in the eye after the original lens was removed becomes clouded, impairing vision. This problem, called a secondary cataract, occurs in about one in four people who have had cataract surgery, months or even years after an artificial lens is implanted. Typically, it is treated by using a laser to make a small opening in the hazy capsule to let light through.
Last full review/revision September 2012 by Kathryn Colby, MD, PhD