Refractive problems that may be encountered include too much correction, too little correction, a prescription imbalance between eyes, aggravation of muscle imbalance problems or a loss of effect from regression. LASIK and PRK may result in overcorrections and undercorrections due to the variability in patient healing patterns and other surgical variables, leaving patients nearsighted, farsighted, or with astigmatism. This may or may not require patients to wear spectacles, contact lenses or undergo further surgery.

Incidence of significant overcorrection: one in 100

Incidence of significant undercorrection: varies with prescription

This is probably the greatest risk during the first 48 to 72 hours following the procedure. You will receive antibiotic drops, both before and after the procedure, to help prevent an infection. Most minor infections are treated and quickly eliminated.

Incidence of serious infection: one in 5000 for LASIK, one in 1000 for PRK

Healing haze is the term for the collagen protein that develops on the surface of your eye following the procedure. Almost everyone develops trace degrees of haze.

It is invisible to the naked eye and very rarely affects your vision. Most patients are not even aware that they have haze. Although treatable in most cases, haze usually clears gradually over many months following the procedure.

Incidence of serious haze: one in 1000 for LASIK, one in 100 for PRK

Regression refers to the tendency of the eye to bounce back somewhat towards your original prescription following laser vision correction. If your vision regresses, you may require an enhancement procedure or a thin pair of glasses. In most cases, the regression experienced is minimal and is accounted for when planning your procedure. In some cases, glasses for night driving may be all that is required by a patient who experiences regression.

Even before having laser vision correction, many people experience poor night vision or night glare (haloes, starbursting) when wearing glasses or contact lenses. Night glare is common immediately following the procedure and will typically last for three or four months. By the time both your eyes are treated or six months have passed, your night glare tends to decrease and you should be back to where you began. However, you may still require glasses for driving at night.

Incidence of significant glare: one in 50

You will not have any pain or discomfort during the laser procedure itself. With new techniques, a relatively small number of patients experience discomfort following the procedure, which can usually be easily treated with medication. Most patients experience some irritation, sensitivity to light, and watering or swelling of their eyes for a few days following the procedure.

Incidence: one in 50 for LASIK, one in 10 for PRK

A small number of patients experience a slight loss of visual sharpness or crispness following laser vision correction (compared to when they were wearing glasses before the procedure). If this occurs, you will lose the ability to read the bottom one to three lines of the eye chart. In some cases, the sharpness returns over a period of six to 12 months. This means that after the procedure, even with glasses or contact lenses, you may not be able to see as clearly as you did prior to the procedure.

Incidence: one in 100

In a few instances, patients will actually gain sharpness of vision, meaning that their vision following the procedure is better than their best-corrected vision before the procedure.

While only about 1 percent of patients have complications with their LASIK procedure, even fewer experience a serious flap-related complication. This may result in loss of best-corrected vision.

Incidence: one in 500

The primary benefits of LASIK are related to the creation of the protective corneal flap. The corneal flap must be of clinically adequate quality, thickness and size to proceed with laser treatment. Corneal flap complications range in severity from those that simply require the procedure to be postponed by three to six months, to those that create permanent corneal irregularities resulting in blurred vision. The most severe LASIK complication is that of corneal perforation, which has been reported several dozen times worldwide. Corneal flap complications that occur after the LASIK procedure during the recovery period include displacement and wrinkling of the corneal flap and epithelial in-growth.

Corneal flap problems include but are not limited to:

Corneal flaps of inadequate size, typically too short, preventing laser treatment, and requiring the LASIK procedure to be repeated in three to six months. Typically no serious visual disturbance although glare and shadowing may occasionally be produced.

Corneal flaps of inadequate thickness, may or may not be adequate for laser treatment, and may result in the procedure being stopped and repeated after three to six months. A thin corneal flap may result in a slow visual recovery over weeks to months and possibly permanently blurred vision with or without laser treatment.

Corneal flaps of inadequate quality or smoothness include a variety of corneal flap problems, which may produce serious permanent corneal irregularities and significant visual blurring. Corneal flap irregularities may be produced because of inadequate suction pressure, inadequate orbital size, inadequate patient cooperation, malfunction or problems with the microkeratome, blade or suction apparatus.

Corneal flaps are routinely hinged either nasally or superiorly beneath the upper eyelid. A corneal hinge is not required for a good visual result, but a hinged corneal flap is more secure and typically heals faster and more smoothly. It is possible, depending upon the corneal shape, the suction ring alignment and the microkeratome, that a free corneal cap may be produced which is not hinged to the cornea. Although the laser treatment can still be performed, if any irregularities in flap quality or thickness are noted, the corneal disc is immediately replaced and allowed to heal. If the free corneal cap is of excellent quality, then the procedure is completed, but special care must be taken during the first 24 to 48 hours not to displace or lose the corneal cap. Loss of the corneal cap may result in scarring, permanent corneal irregularity and the need for more invasive surgery.

Corneal perforation is the most serious LASIK complication. Corneal perforation is prevented by the microkeratome depth plate, which is checked before each and every procedure. Some microkeratomes have fixed corneal depth plates. Perforation of the cornea requires corneal suturing, and the need for an intraocular lens implant as the natural lens is usually lost or damaged. It should be appreciated that corneal perforation may also potentially result in infection, the need for a corneal transplant or even rarely blindness.

Corneal flap displacement, partial or complete, occurs during the early post-operative period, typically during the first 12 to 24 hours, but may occur days to weeks later with trauma. Care should be taken to protect the eyes from trauma, as well as avoiding rubbing the eyes or forcefully closing the eyes during the first week following LASIK. Partial displacement of the corneal flap may result in corneal striae or wrinkles, which blurs vision both qualitatively and quantitatively. Most corneal striae are treatable but some may be resistant to treatment, especially in highly nearsighted patients. Complete displacement of the corneal flap is often painful and requires urgent replacement. There is a higher risk of epithelial in-growth and infection with corneal flap displacement.

Epithelial in-growth occurs during the first month following LASIK and is more likely to occur in patients with an abnormal or weakly adherent protective layer, for which age is a factor. Epithelial in-growth is produced when epithelial surface cells grow underneath the corneal flap during the healing of the corneal flap incision. Epithelial in-growth is more common with any trauma or breakdown of the epithelium, which is more common in LASIK enhancement procedures and long-term contact lens wearers. Treatment of this condition involves lifting the flap and clearing the cells away. Although most small areas of epithelial in-growth need only be monitored, untreated large areas of epithelial in-growth may distort vision and may actually damage the flap integrity if severe and progressive.