LASIK refractive surgery is an elective procedure – meaning it’s not medically necessary.  You can safely correct your vision with eyeglasses or contact lenses instead of choosing LASIK.


By choosing LASIK surgery to correct your vision, you are accepting a certain amount of risk.  No surgical procedure (including LASIK) will have a perfect outcome 100% of the time.


Thankfully, LASIK is very safe and the frequency of serious complications is quite low.  But you should fully understand the risks and potential complications of LASIK before making your decision about whether or not to have the procedure done.  


Two Types of LASIK Complications


LASIK complications can be divided into two distinct categories: 1) those that occur during surgery (intra-operative complications); and 2) those that occur after surgery (post-operative complications).


Frequency of Intra-Operative Complications

Studies1,2,3 suggest that when LASIK is performed by an experienced surgeon, the incidence of intra-operative complications is less than 2 percent.


Frequency of Post-Operative Complications

Post-operative complications are more frequent.  Research1 suggests that when an experienced surgeon performs LASIK, the incidence of post-operative complications is approximately 8 percent.


Yesterday’s Statistics May Not Be Valid Today


Refractive surgery is a rapidly-changing science.  Statistics related to risks and complications of LASIK and other forms of refractive surgery are constantly changing.  Figures that may be quite accurate at the time the research is performed may already be obsolete for the time you choose to have LASIK performed.


As surgical instruments become more sophisticated and surgical techniques continue to evolve, most researchers believe the incidence of complications will continue to decline.


We believe it’s important for you to research and understand the risks and potential complications of LASIK before you decide to proceed with refractive surgery.  But in addition to your online research, we highly recommend you discuss the risks and potential complications of LASIK personally with your refractive surgeon of choice.  Your surgeon will be better able to discuss the risks and frequency of complications that apply to your particular situation.


Intra-Operative LASIK Complications


Intra-operative complications are surgical complications that occur during the LASIK procedure.  These can be divided into two categories: 1) complications that occur during the creation of the corneal flap (flap complications); and 2) complications that occur during the laser treatment itself (laser complications).


Flap Complications


The first step in the LASIK procedure is the creation of a flap on cornea.  This is usually performed with a surgical tool called a microkeratome.  The microkeratome is placed on the surface of the cornea and is held in place with suction.  A surgical blade within the instrument cuts the flap, leaving a small hinge to keep the flap partially attached to the rest of the cornea.


Flap complications can occur if suction is lost while the microkeratome blade is cutting or the instrument malfunctions in some manner. 


Types of flap complications include:

  • Irregular or incomplete flaps.

  • Flaps that are too small or too thin.

  • Buttonholes (small holes or tears in the center of the flap).

  • Free caps (flaps without a hinge).


Research3 suggests the incidence of flap complications is 2 percent or less.


In most cases, flap complications cause no permanent decrease in visual acuity.  When a flap complication occurs, the surgeon will typically halt the LASIK procedure and re-position the flap.  LASIK can then be re-scheduled a few months later after the flap has healed.


Laser Complications


Laser complications are rarely seen.  Though studies that appeared in 1999 or earlier reported a small incidence of de-centered treatment zones and central islands (elevated areas of cornea within the laser treatment zone), more recent clinical studies submitted to the U.S. Food and Drug Administration (FDA) for market approval of laser systems for LASIK report no occurrences of de-centered laser treatments (also called ablations) or central islands.4


Post-Operative Complications


Post-operative complications are complications associated with healing that occur after the patient leaves the operating room.


Studies5,6 suggest that approximately 1 to 6 percent of LASIK patients experience some type of post-operative complication.  These complications include:


Residual Refractive Error and Regression


It’s unrealistic to expect LASIK to produce 20/20 visual acuity in all cases.  Every eye heals differently, and the rate of healing can affect visual results. Patients whose corneas heal faster or slower than normal may experience an under-correction or over-correction of their refractive error (i.e. nearsightedness, farsightedness or astigmatism).3


In addition, changes can take place in the shape and thickness of the cornea during the healing process.  These changes can result in a slight regression (loss of corrective effect) of the immediate LASIK result over time.  In general, the stronger your eyeglasses prescription is prior to LASIK, the more risk there is that there may be some regression.  This is especially true for the treatment of high amounts of farsightedness.3


Approximately 10 percent of LASIK procedures result in under-corrections (where the treatment is insufficient to produce acceptable visual acuity), over-corrections (where a treatment for nearsightedness results in a mild amount of farsightedness or vice versa) or regressions (where the surgical effect is lost during the healing process).


In most cases, these problems can be corrected and visual acuity can be improved with a second LASIK procedure.  These follow-up LASIK procedures are called an enhancements.


When they are necessary, enhancements are typically performed 6 to 9 months after the initial LASIK procedure.  It is usually best to wait this long to make sure results from the first LASIK are completely stable.


In some cases (particularly with thin corneas) enhancement LASIK procedures cannot be performed.  If it appears you require an enhancement procedure, your surgeon will re-measure the thickness of your cornea to determine if an enhancement is possible.  


Glare and Reduced Contrast Sensitivity


Glare and decreased contrast sensitivity are common post-operative complications in the weeks following LASIK.  In most cases, these problems diminish with time. 


Glare is a dazzling sensation produced by relatively bright light, which causes discomfort and/or interferes with visual acuity. Glare is often reported as halos around lights (particularly vehicle headlights and tail-lights at night) and starbursts or streaks around streetlights.


Contrast sensitivity is the lowest contrast level (i.e. the difference between the lightest and darkest parts of something) a person can discern when looking at something of a constant size.  This is a more sensitive measure of visual acuity than the wall chart used during an eye exam. 


The wall chart method (called Snellen acuity – named after the Dutch ophthalmologist who devised the test in 1862) measures visual acuity only with high contrast targets – black letters on a white background. 


In real life, most visual tasks are not black-on-white scenarios.  Especially at night, good vision depends on our ability to distinguish shades of similar colors or different shades of gray.  Driving at night is a good practical test of contrast sensitivity.  A person with good contrast sensitivity is able to spot a deer (for example) alongside a dark roadway at night better than a person who has poor contrast sensitivity – even if both individuals see essentially the same sized letters on a high-contrast wall chart during an eye exam.


For several weeks after LASIK, a person’s contrast sensitivity may be significantly reduced despite being able to see the wall chart in an exam room quite well.


This reduction in contrast sensitivity is difficult to quantify because contrast sensitivity testing is not frequently performed in routine eye exams or LASIK pre-operative or post-operative exams.  (Contrast sensitivity testing requires charts that typically show alternating light and dark lines of different widths, orientations, and levels of contrast.)


Studies8-14 that have investigated the effect of LASIK on contrast sensitivity suggest:

  •       High-contrast visual acuity (as measured on the wall chart in an exam room) is frequently nearly the same as a patient’s best-corrected visual acuity prior to surgery within 1 week after LASIK.  But low-contrast acuity (i.e. contrast sensitivity) frequently remains reduced one line on an acuity chart for up to six months after LASIK.

  •       Contrast sensitivity is nearly always back to normal six months after LASIK.  

  •            Pupil size affects the quality of vision after LASIK.  Patients with large pupils may experience more glare and a greater reduction in contrast sensitivity than patients with smaller pupils.  And since pupils dilate in dim lighting, LASIK patients may notice a reduced quality of vision in a darkened environment compared to well-lit surroundings.

  •            Contrast sensitivity may actually improve after LASIK (compared to pre-operative levels) for some patients with high amounts (over 9 diopters) of nearsightedness. 


Dry Eyes


Most patients experience mild to moderate symptoms of dry eyes for a few weeks after LASIK.  These symptoms include:

  •            A sandy, gritty feeling to the eyes.

  •            A foreign body sensation – the feeling that something is in your eye.

  •            A burning sensation.

  •            A “heavy” feeling to the eyes.

  •            Sensitivity to light.

  •            Occasionally, pain in the eyes.