Eye Pathologies (Cataracts)

Cataracts

What is a cataract?
A cataract is a cloudy or opaque area in the lens of the eye. The lens is located behind the pupil and iris. It helps focus light onto the retina, the light-sensitive tissue that lines the inside of the back of the eye. Usually, the lens is transparent. But if it becomes clouded, the passage of light is obstructed and vision may be impaired (Figure 1).

Figure 1.

What causes a cataract?
When a cataract forms, there is a change in the chemical composition of the lens, but scientists do not know exactly what causes these chemical changes. The most common form of cataract is related to aging, although this type can occur at age 50 or even earlier. Cataracts also may be associated with diabetes, other systemic diseases, drugs, and eye injuries. Sometimes babies are born with congenital cataracts or develop them during the early years of life.

What are the symptoms of a cataract?
Here are some signs of cataract:
- Cloudy, fuzzy, foggy, or filmy vision.
- Changes in the way you see colors.
- Problems driving at night because headlights seem too bright.
- Problems with glare from lamps or the sun.
- Frequent changes in your eyeglass prescription.
- Double vision.
- Better near vision for awhile only in farsighted people.
These symptoms also can be signs of other eye problems.
See your eye doctor to find out what you have and how it can be treated.

How Is a Cataract Diagnosed?
A regular eye exam is all that is needed to find a cataract. Your eye doctor will ask you to read a letter chart to see how sharp your sight is. You probably will get eye drops to enlarge your pupils (the round black centers of your eyes). This helps the doctor to see the inside of your eyes. The doctor will use a bright light to see whether your lenses are clear and to check for other problems in the back of your eyes.
Other eye tests may also be used occasionally to show how poorly you see with cataract or how well you might see after surgery:
- Glare test.
- Contrast sensitivity test.
- Potential vision test.
- Specular photographic microscopy.
Only a few people need these tests.

When should a cataract be removed?
A cataract should be removed surgically when it has progressed to the point where resulting vision problems interfere with one's daily activities. A second reason for cataract surgery, more urgent but less common than the first, is that the cataract has become completely opaque (mature, Figure 2). It is possible for a mature cataract to swell and even disintegrate inside the eye. Such changes can permanently endanger vision.

Figure 2.

With congenital cataracts, it used to be standard practice to postpone surgery until the child was at least 6 months old. Recently, however, cataracts have been removed from the eyes of newborn infants with good results. Early removal of severe congenital cataract(s) is an important advance because it reduces the risk of visual loss resulting from the disuse of one or both eyes during childhood.

How are cataracts treated?
Treating cataracts really involves two steps. The first is removal of the clouded lens by an ophthalmologist. Surgery is the only method proven effective for removing cataracts. The second is finding an appropriate substitute for the natural lens. The decision about which substitute lens to use is usually made before surgery.
There are two general methods of removing a cataract: intracapsular and extracapsular extraction of the lens. Intracapsular extraction is sometimes used to remove senile cataracts. In this method, the entire lens, including its capsule, is removed.
Extracapsular extraction involves removal of most lens tissue but the back part of the lens capsule is left in place. In infants and young children, whose lenses are relatively soft, the lens tissue may be withdrawn through a hollow needle, a procedure called aspiration. A variety of extracapsular techniques are also used to remove the lens in adults.
One technique is called phacoemulsification. High-frequency sound vibrations (ultrasound) are used to soften and liquefy the lens so it can be aspirated through the needle.
Phacoemulsification should not be confused with another form of eye surgery, photocoagulation, in which laser light--not ultrasound--is used to treat some eye disorders other than cataract. A laser cannot remove a cloudy lens or make it clear again. However, some doctors may use a laser to open the front part of the lens capsule before removing the lens or to help patients who develop "after-cataract."

How safe is cataract surgery?
Cataract surgery is one of the most successful operations done today--more than 90 percent of the people who have this surgery find that they can see better. Complications may occur, but most are treatable. Serious complications that threaten vision are rare. Certain people may not benefit much from cataract surgery. They include people whose cataracts are not advanced enough to impair vision seriously and those whose vision is impaired by another eye disease as well.
In summary, each cataract patient should discuss the possibility of surgery with the doctor who examines his or her eyes to determine whether the potential benefits of cataract surgery outweigh the risks. It is also very important to decide in advance, with the help of the doctor, what form of substitute lens would be most suitable. Patients may want to get a second opinion on the advisability of surgery and on the most appropriate substitute lens to use after surgery.

What are the choices for a substitute lens?
There are three options for replacing the natural lens removed in cataract surgery: eyeglasses, contact lenses, or an intraocular lens implant. Each has advantages and drawbacks.
Eyeglasses. This is a safe and time-proven solution to the problem of seeing without a natural lens. But cataract eyeglasses can have some unpleasant effects. Patients may be bothered by the fact that these glasses magnify objects 20-35 percent, affect depth perception until the person relearns how to judge distances, and limit side vision.
If only one eye requires cataract surgery, eyeglasses may well cause problems because the person is unable to fuse the different-sized images formed by the operated and unoperated eyes. Such patients are often advised before surgery that it would be best to use a contact lens, or have a lens implant.
Contact lenses. These usually provide better vision than eyeglasses and also are quite safe if handled and maintained properly. A contact lens may be especially helpful after cataract extraction in one eye. With a contact lens in the operated eye, the difference in the size of the images seen by the two eyes is much smaller. Soft contact lenses are commonly used for cataract patients.
Another option is the extended-wear contact lens. These lenses can be left in the eye for a longer period of time without being removed, even for sleep. They may be especially useful for people who have trouble inserting and removing a contact lens, because an eye care specialist can remove and clean them periodically. However, extended-wear lenses have some disadvantages: They are very fragile; some serious infections have been reported; their long-term safety is still being assessed; and they do require periodic removal, cleaning, and reinserting.
Intraocular lenses. These devices, sometimes called IOLs, are clear plastic lenses that are implanted in the eye during the cataract operation. Lens implants have certain advantages: They usually eliminate or minimize the problems with image size, side vision, and depth perception noted by people who wear cataract eyeglasses. Also, because lens implants remain in the eye and do not have to be removed, cleaned, and reinserted, they are more convenient than contact lenses. This is particularly true for people who have physical problems that would make it difficult for them to carry out the procedures involved in using contact lenses.
Because of these advantages, lens implants have been used with increasing frequency in recent years. About three-fourths of all people now undergoing cataract surgery have an IOL inserted at the same time, and the vast majority are very pleased with the results. Of course ophthalmologists will continue to study IOLs for many years in an effort to assess the long-term effects of implantation on the eye as well as the short-term complications.

What happens after surgery?
Most people who undergo cataract surgery are treated as outpatients and can go home the same day. For others, a stay in the hospital of 1-3 days may be required. In either case, during the early stages of recovery, patients need to take special care to avoid strenuous physical activity.

Can a Cataract Return?
A cataract cannot return because all or part of the lens has been removed. However, in about half of all people who have extracapsular surgery or phacoemulsification, the lens capsule becomes cloudy. This cloudiness of the lens capsule, if it occurs, usually develops a year or more after surgery. It causes the same vision problems as a cataract does.
The treatment for this condition is a procedure called YAG capsulotomy. The doctor uses a laser (light) beam to make a tiny hole in the capsule to let light pass. This surgery is painless and does not require a hospital stay (Figure 3).
Most people see better after YAG capsulotomy, but, as with cataract surgery, complications can occur. Your doctor will discuss the risks with you. YAG capsulotomy should not be performed as a preventive measure.

Figure 3.

Is Cataract Surgery Right for Me?
Most people who have a cataract recover from surgery with no problems and improved vision. In fact, serious complications are not common with modern cataract surgery. This type of surgery has a success rate of 95 percent in patients with otherwise healthy eyes. But no surgery is risk free. Although serious complications are not common, when they occur they could result in loss of vision.
If you have a cataract in both eyes, experts say it is best to wait until your first eye heals before having surgery on the second eye. If the eye that has a cataract is your only working eye, you and your doctor should weigh very carefully the benefits and risks of cataract surgery.
You will be able to make the right decision for yourself if you know the facts. Ask your doctor to explain anything you do not understand. There is no such thing as a "dumb" question when it comes to your health.
Here are some questions you might ask:
- Do I need surgery right away?
- If not, how long can I wait?
- What are my personal risks?
- What benefits can I expect?
- If I choose surgery, which type is best for me?
- Which lens replacement is best for me?
- What are the chances of developing cloudiness in the lens capsule after cataract surgery?

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