Cataract is the word used to describe an area of increasing cloudiness in the lens of the eye — the lens of the eye is located behind the iris -the coloured part of the eye. A cataract may begin as a white spot at the edge of the lens or as a haze at the centre of the lens and gradually worsens until the vision is badly blurred.

Clouded vision can make it more difficult to read, drive a car or see the expression on a friend's face. Cataracts commonly affect distance vision and cause problems with glare. They generally don't cause pain, double vision with both eyes open or abnormal tearing.

Most cataracts develop slowly and don't disturb your eyesight early on. But as the clouding progresses, the cataract eventually interferes with your vision.

In the early stages, stronger lighting and eyeglasses can help you deal with the vision problems. But at some point, if impaired vision jeopardizes your normal lifestyle, you might need surgery. Fortunately, cataract removal is one of the safest, most effective and most common surgical procedures.

What happens during cataract surgery?

Important advances in surgical technique and more sophisticated technology have helped make surgery a safe and effective treatment for cataracts. Two things happen during cataract surgery — the clouded lens is removed, and a clear artificial lens is implanted.

Prior to surgery, your eye doctor measures the size and shape of your eye to determine the proper lens implant power. This measurement is made with a painless ultrasound test. Cataract surgery is typically an outpatient procedure that takes less than an hour. Most people are awake and need only local anesthesia. On rare occasions some people may need general anesthesia.

Surgical methods used to remove cataracts include:

• Phacoemulsification. During this procedure your surgeon removes the cataract but leaves most of the outer layer (lens capsule) in place. The capsule helps support the lens implant when it's inserted.

• During phacoemulsification, phaco for short, your surgeon makes a small incision, about 1/8 inch, which is about 3 millimeters (mm), where the cornea meets the conjunctiva and inserts a needle-thin probe. The surgeon then uses the probe, which vibrates with ultrasound waves, to break up (emulsify) the cataract and suction out the fragments. The lens capsule is left in place to provide support for the lens implant.

• Extracapsular cataract extraction. If your cataract has advanced beyond the point where phacoemulsification can effectively break up the clouded lens, your surgeon may do an extracapsular cataract extraction. This procedure requires a larger incision, about 3/8 of an inch (10 mm), where the cornea and sclera meet. Through this incision your surgeon opens the lens capsule, removes the nucleus in one piece and vacuums out the softer lens cortex, leaving the capsule in place.

Once the cataract has been removed through phacoemulsification or the extracapsular method, a clear artificial lens is implanted into the empty lens capsule to replace the original clouded lens. This lens implant, also known as an intraocular lens (IOL), is made of plastic, acrylic or silicone. It requires no care and becomes a permanent part of your eye. Whether or not you wear glasses, after surgery you'll likely need reading glasses.

Some IOLs are rigid plastic and implanted through an incision that requires several stitches (sutures) to close. However, many IOLs are flexible, allowing a smaller incision that requires no stitches. The surgeon can fold this type of lens and insert it into the empty capsule where the natural lens used to be. Once in place the lens unfolds to about 1/4 inch (6 mm).

With phacoemulsification and foldable lens implants, surgical incisions are very small, and no sutures are required. If all goes well, you'll heal fast and your vision will start to improve within a few days. If your surgery requires a larger incision and sutures, full healing will take longer.

Normally you can go home on the same day as surgery, but you won't be able to drive, so make sure to arrange for a ride home. It's also a good idea to make sure you have extra help because your doctor may limit activities like bending and lifting for a few days. You'll typically see your eye doctor the next day, the following week and then again after a month so that he or she can check the healing progress.

It's normal to feel mild discomfort for a couple of days after surgery. Avoid rubbing or pressing on your eye. Clean your eyelids with tissue or cotton balls to remove any crusty discharge. You may wear an eye patch or protective shield the day of surgery. Your doctor may prescribe medications to prevent infection and control eye pressure. After a couple of days, all discomfort should disappear.

Contact your doctor immediately if you experience any of the following signs or symptoms after cataract surgery:

• Vision loss

• Pain that persists despite the use of over-the-counter pain medications

• A definite increase in eye redness

• Light flashes or multiple spots (floaters) in front of your eye

• Nausea, vomiting or excessive coughing

• Astigmatism

• Nausea

• vomiting

Most people need to wear glasses after cataract surgery. Astigmatism — a focusing problem that occurs when your cornea isn't curved evenly in all directions — is common but is less of a problem when the surgery involves a small incision. Your doctor will let you know when your eyes have healed enough for you to get a final prescription for eyeglasses.

Complications after cataract surgery are relatively rare, and most can be treated. They include inflammation, infection, bleeding, swelling, retinal detachment and glaucoma. The risks are greater for people who have other eye diseases or serious medical problems. Occasionally cataract surgery fails to improve vision because of conditions such as glaucoma or macular degeneration. It is important to evaluate and treat these other eye problems, if possible, before making the decision to proceed with cataract surgery.

If you have cataracts in both eyes, your doctor will treat one eye at a time, and it's usually a month or two before you can schedule surgery for the other eye.

You may have heard of a second cataract, or after cataract. This condition occurs when the back of the lens capsule — the part of the lens that wasn't removed during surgery and that now supports the lens implant — eventually becomes cloudy and blurs your vision. Another term for this condition is posterior capsule opacification (PCO). PCO can develop months or years after cataract surgery. It happens about 25 percent of the time. The gradual clouding is the result of cell growth on the back of the capsule.

Treatment for PCO is simple and quick. It involves a technique called YAG laser capsulotomy, in which a laser beam is used to make a small opening in the clouded capsule to let light pass through. Capsulotomy means "cutting into the capsule," and YAG is an abbreviation of yttrium-aluminum-garnet, the type of laser used for the procedure.

Laser capsulotomy is a quick, painless outpatient procedure that usually takes less than five minutes. Afterward, you typically stay in the doctor's office for about an hour to make sure your eye pressure isn't elevated. In some people, particularly those who have glaucoma or are extremely nearsighted, YAG laser surgery can raise eye pressure. Other complications are rare but can include swelling of the macula and a detached retina.