LASIK is the most commonly performed laser eye surgery to treat myopia , hyperopia and astigmatism.

The word "LASIK" is an acronym for "laser-assisted in situ keratomileusis."

Like other types of refractive surgery, the LASIK procedure reshapes the cornea to enable light entering the eye to be properly focused onto the retina for clearer vision.

LASIK surgery is essentially pain-free and takes only about 15 minutes for both eyes. The results improved vision without eyeglasses or contact lenses begin immediately after the procedure and vision usually continues to improve and stabilize over a few days.

If you're not a good LASIK candidate, a number of other vision correction surgeries are available, such as PRK and LASEK laser eye surgery.

PRK (Photorefractive keratectomy) was the first approved laser eye surgery for vision correction, and LASEK (laser-assisted sub-epithelial keratectomy) came later. There are some differences between the two.

* With LASEK eye surgery, the surgeon cuts a thin flap over the cornea to access the treatment area. Once the correction is complete, the shutter is replaced.

*With PRK eye surgery, the surgeon removes the entire outer (epithelial) layer of the cornea to access the treatment area. After surgery, the eye heals naturally and develops a new epithelial layer.

For patients with thinner corneas, PRK is generally the preferred option over LASEK. However, PRK requires a longer healing time than LASEK, which is one of the reasons many patients switch to LASEK.

In addition to faster recovery, LASEK patients generally experience less discomfort than PRK patients. They also have a lower risk of infection and other side effects such as inflammation and blurred vision.

With PRK, the surgeon has access to the full thickness of the stroma compared to what is accessible with the LASEK flap. For patients with thinner corneas or those who have already undergone a LASEK procedure, this additional access may be required for optimal results.

LASEK and PRK treatments provide excellent visual results and the absence of far vision glasses for almost all patients. Prk and Lasek generally provide equivalent visual results. So why would anyone choose lasek over prk? Some patients prefer LASEK for its faster healing, and others prefer PRK for its added safety.

Your ophthalmologist will perform a thorough eye exam to ensure your eyes are healthy enough for the procedure. He or she will evaluate: the shape and thickness of your cornea; pupil size; refractive errors (myopia, hyperopia and astigmatism); as well as any other eye conditions.

The tear film on the surface of your eyes also will be evaluated, and a precautionary treatment may be recommended to reduce your risk of developing dry eyes after LASIK.

Usually, an automated instrument called a corneal topographer is used to measure the curvature of the front surface of your eye and create a "map" of your cornea.

With wavefront technology associated with custom LASIK, you also are likely to undergo a wavefront analysis that sends light waves through the eye to provide an even more precise map of aberrations affecting your vision.

Your eye doctor also will ask you about your general health history and any medications you are taking to determine if you are a suitable candidate for LASIK.

You should stop wearing contact lenses for a period of time advised by your doctor (typically around two weeks) before your eye exam and before the LASIK procedure. This is because contact lens wear can temporarily alter the natural shape of your cornea.

Before your LASIK surgery begins, numbing eye drops are applied to your eye to prevent any discomfort during the procedure. Your doctor may also give you some medication to help you relax.

Your eye will be positioned under the laser, and an instrument called a lid speculum is used to keep your eyelids wide open.

The surgeon uses an ink marker to mark the cornea before creating the flap. A suction ring is applied to the front of your eye to prevent eye movements or loss of contact that could affect flap quality.

After the corneal flap is created, the surgeon then uses a computer to adjust the excimer laser for your particular prescription.

You will be asked to look at a target light for a short time while your surgeon watches your eye through a microscope as the laser sends pulses of light to your cornea.

The laser light pulses painlessly reshape the cornea, although you may feel some pressure on your eye. You'll also hear a steady clicking sound while the laser is operating.

LASIK is performed on each eye separately, with each procedure taking only about five minutes.