The reported amount of serious complications following LASIK surgery is about 5% or slightly lower.  The most important factor affecting surgical outcome is the experience of the surgeon: many studies show that as surgical experience increases, complications decrease, with the surgeon reaching a plateau around 1,000 procedures.  Other factors that can affect surgical success include:

• High degrees of hyperopia (farsightedness), myopia (nearsightedness), or astigmatism
• Large pupils (if the diameter of the pupil at full dilation is greater than the diameter of the treatment zone, vision can be impaired, especially at night or under low lighting)
• Pre-operative dry eyes
• Eye diseases or problems such as keratoconus or "floaters"

Most complications are treatable or manageable, while others can pose serious risks to your vision.  Below is a list of possible complications and how they can be treated if they do occur:

Night vision and contrast problems

• Contrast sensitivity
• Double Vision and Ghosting
• Halos
• Starbursts

Flap Complications

• Striae
• Ectasia
• Buttonhole flap
• Free flap

Other complications

• DLK
• Central Island
• Dry eye
• Infection

Night Vision and Contrast Problems

Contrast sensitivity - the ability to differentiate an object from its surrounding background.  The decrease in contrast sensitivity is a relatively common occurrence following LASIK surgery, especially in patients with high amounts of myopia.  Like the Snellen eye chart (the one with the big E at the top) that measures visual acuity, there are similar charts and tests to measure contrast sensitivity, with 20/20 quantified as normal contrast.  Visual acuity measures how well the eye can see objects that are black and white at a given distance, while contrast sensitivity measures the ability to see under low light conditions, such as driving at night.

After LASIK, almost all patients experience some (usually small) amount of decrease in contrast sensitivity, but usually return to normal within the first few weeks or months following surgery.  If loss of contrast sensitivity is excessive, it can lead to increased night vision problems.

Double Vision and Ghosting - the appearance of a second, usually fainter, image of an object creating a blurred vision.  This complication is usually a result of irregular astigmatism induced by surgery.  Like many other LASIK related vision problems, ghosting has a tendency to subside over time as the cornea heals, although both mild and severe cases have been reported as permanent complications. 

Initially, anti-inflammatory drops are prescribed to help reduce corneal swelling.  In persistent cases an enhancement or re-treatment could be possible to help correct vision, but in most instances a proper fitting with rigid gas permeable contact lenses (RGPs) is the best option for reducing ghosting.

Halos - the appearance of a halo around lights.  Due to corneal swelling, the appearance of halos for the first few weeks following LASIK is quite normal.  If halos persist, however, it may be necessary to have a re-treatment or use corrective lenses or glasses.

Starbursts - describes the complication that causes lights to appear blurred with spikes or rays of light radiating from the center of the light source.  Starbursts usually only affect nighttime vision, but in some cases can appear around lights at any time of the day.  For many patients this complication will subside within a month to six weeks.  For other patients, treatments can include additional surgery, the diagnosis and treatment of dry eye (if this is thought to be the cause), prescription eye drops that restrict the pupil size at night, or contact lenses.   The type of treatment necessary will be different for each individual case.

Flap Complications

Striae - wrinkles that occur in the corneal flap following LASIK surgery.  Striae are usually a result of correction of myopia, but can occur during hyperopic correction as well.  In some cases striae may not impede vision, and will not require correction.  In other cases surgical correction is necessary to re-lift and smooth the flap.

Ectasia - When performing LASIK on a myopic and/or astigmatic eye, the purpose is to flatten the cornea, allowing proper refraction.  When the corneal flap is cut too deep, too much tissue is removed, or the cornea was too thin for such a procedure, the remaining corneal tissue can be too thin to handle normal pressure and begin to weaken.  As it weakens it can bulge or otherwise deform, causing residual myopia and induced astigmatism.  The occurrence of such a complication is referred to as ectasia.

In some cases contact lenses can be worn to increase visual acuity, while in severe cases of ectasia a corneal transplant is necessary.

Buttonhole flap - this refers to a tear, rip, or uneven cut resulting in a partial cornea flap.  When the microkeratome blade is placed incorrectly, too worn or used, or is not the right fit for the given eye, a partial an uneven cut can result.  In other cases the corneal flap will tear or rip when it is being lifted or placed back over the eye.  When a buttonhole forms the surgery is stopped and the flap gently replaced.  If surgery is continued after a buttonhole flap is created, scarring and astigmatism can increase, worsening vision.

In 3 to 6 months, once the flap has had time to heal, the flap can be recut, usually with the use of a different microkeratome or by increasing the diameter of the intended flap.

A buttonhole flap can produce scarring that will impair vision, making close follow up with your ophthalmologist important.  Patients with extraordinarily steep corneas are at higher risk for the buttonhole flap complication.

Free Flap - this occurs when the flap is cut all the way through, leaving no connecting hinge.  This usually occurs as a result of loss of suction while the microkeratome blade is passing across the eye.  As long as there are no irregularities of the flap, including rips and an uneven cut, the surgery can be performed as normal and the flap replaced without further complication.  In the most serious cases the flap can be lost or suffer irreparable damages. 

Other Complications

DLK (Diffuse Lamellar Keratitis also called "Sands of Sahara") - inflammation of the cornea caused by a reaction to debris accumulated underneath the flap.  DLK is usually indicated in stages from 1, which consists of debris outside the center of the eye, to 4, which includes stromal melting and central tissue loss.  An estimated 1% of LASIK patients develop DLK with approximately 1 in 5,000 progressing to stage 4 status.  Most ophthalmologists will treat stage 1 and 2 DLK with topical steroids or oral anti-inflammatories, but if the patient does not respond to treatment within a few days, additional surgery to lift the flap and irrigate the infected area may be necessary.

Central Islands - when treatment with the laser is not consistent across the entire treatment area, a protruding section of the cornea that is not in proportion with the rest of the surface can cause vision problems.  This raised area, or central island, is basically an under treated area of the cornea, usually in the center, while the rest of the eye was treated to the correct specifications.  In some cases this complication can be self-correcting within a month.  Most of the time, however, a central island requires re-treatment, where the flap is raised and laser energy applied to create a more uniform corneal surface.

Dry Eye - In some cases LASIK can induce the occurrence of chronic dry eye.  To correct this problem or help relieve the symptoms, your ophthalmologist may recommend treatments including artificial tear eye drops or punctual plugs that impede the draining of eye moisture.  In many instances the effects associated with dry eye will disappear and treatment can be stopped.  In other cases symptoms will persist and treatment continued for an indeterminate amount of time.

Infection - Though infection is extremely rare, if it does occur it can lead to permanently damaging eye problems.  As with any surgery, a sterile operating room and careful attention to post-operative care are essential in preventing infection.  Avoiding such activities as swimming, basketball, and other like pastimes for the first few weeks will help reduce the chance of infection.  If any signs of infection are detected you should visit your ophthalmologist immediately, as treatment and medication can cure infection if it is caught early enough.