What are the risks?

LASIK corrects myopia by reshaping the cornea in a relatively safe procedure that usually lasts no more than 20 minutes.

During the operation, a thin flap is cut through the top layer of the cornea using either laser or a precise blade. The flap is folded out of the way and a laser is used to remove parts of the corneal tissue. Then the flap is replaced and left to heal naturally without stitches.

But as with all surgeries, it comes with risks and complications, although it should be noted that these are often treatable.

Here is a guide to the more common ones.

DRY EYES

Caused by: The severance of corneal nerves that are connected to the brain when the surface of the cornea is cut to create the flap. These nerves normally instruct the brain to lubricate the eye when it is dry by tearing.

Affects: At first, almost every patient who undergoes Lasik. But six months after the procedure, more than 90 per cent of patients will have recovered.

Treatment: Frequent application of lubricating eye drops until the problem is resolved. Less than 5 per cent of patients will suffer from permanent dry eyes - severity is usually mild to moderate - and they will need to apply eye drops daily.

HALOS AND GLARES

Caused by: The pupil expanding beyond the lasered area of the cornea or laser ablation zone. When that happens, light will pass through both treated and untreated areas of the cornea before reaching the pupil, which leads to optical interference effects, causing glare and haloes at night. It also affects those with a higher degree of astigmatism, as their astigmatism might not be fully corrected.

Affects: About 5 to 20 per cent of patients, especially those with greater degrees of myopia and astigmatism. It also affects those whose pupils are large under dim light conditions.

Treatment: None necessary. In most cases, the halo and glare effects will go away after six months. For the minority who are affected for life, they may have to wear glasses or apply special eye drops to reduce the glare at night.

OVERCORRECTION AND UNDERCORRECTION

Caused by: The different healing speeds of the cornea after the surgery. Those who heal too quickly will have undercorrection and still be short-sighted, while those who heal too slowly will be overcorrected and be long-sighted. But usually this is confined to within 100 degrees either way.

Affects: About 2 to 5 per cent of patients, especially those with myopia of more than 600 degrees.

Treatment: An enhancement - a second surgery - can be done if the patient wishes and has enough corneal tissue for another procedure. If not, the patient may have to go back to wearing glasses. They may also wear contact lenses, except for those with very flat corneas or who had myopia of more than 600 degrees before the surgery. This is because the cornea would be a lot flatter after the procedure and the lenses may not fit well.

EYE INFLAMMATION (DIFFUSE LAMELLAR KERATITIS)

Caused by: The eyes' antibodies reacting to foreign cells that are introduced between the flap and the cornea during the operation.

Affects: Between 0.5 and 3 per cent of patients.

Treatment: Steroid eye drops to curb the inflammation for mild cases. For more serious cases, the patient has to return to the operating room to have the corneal flap lifted so that the debris underneath can be flushed out, using a balanced salt solution. In almost all cases, this will be resolved without further treatment needed.

CORNEAL FLAP PROBLEMS

Caused by: A microkeratome machine - the machine that cuts the corneal flap - that did not function well, or a patient that has a cornea that is either too flat or steep, making it harder to make a good cut to create the flap. This results in a hole being cut in the cornea, an incomplete flap being cut, or a flap that is completely detached from the cornea.

Affects: About 0.2 to 0.5 per cent of patients.

Treatment: In most cases, the improperly cut cornea flap can be replaced immediately to wait for it to heal by itself, before a repeat procedure is carried out at least three months later.

LOSS OF VISION

Caused by: Infection of the eye by bacteria, which can lead to corneal scarring and blindness.

Affects: About 0.01 per cent of patients or less.

Treatment: Antibiotic eye drops to kill the bacteria, then steroid eye drops to reduce inflammation. But if the infection has affected the cornea and resulted in bad scarring, a cornea transplant may be needed.

Information provided by Dr Gerard Chuah, a consultant ophthalmologist at Total EyeCare Center at Mount Elizabeth Medical Centre.