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

Studies^1,2,3 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:

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.

Studies^5,6 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.)

Studies^8-14 that have investigated the effect of LASIK on contrast sensitivity suggest:

Dry Eyes

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

It's believed that one reason dry eye symptoms occur after LASIK is because the creation of the corneal flap during the procedure severs some of the corneal nerves that provide feedback to the tear glands.  Damage to these corneal nerves desensitizes the cornea and temporarily reduces the flow of tears to the eyes.  As your eyes heal after LASIK, the corneal nerve endings regenerate, allowing corneal sensitivity and tear volume to gradually return to normal.

Studies^15-17 have shown that some patients may experience dry eye symptoms for several months after LASIK.  This is particularly true for patients who have mild or moderate dry eyes prior to surgery.  Because LASIK can worsen a dry eye condition, some individuals with dry eyes may not be good candidates for LASIK surgery.

Your LASIK surgeon will instruct you to use artificial tears very frequently for several weeks after surgery to keep your eyes moist and comfortable.  They may also recommend that you use a lubricating ointment on your eyes at bedtime.  Be sure to follow these instructions to keep your eyes comfortable and help facilitate the healing process after LASIK.

Flap Irregularities

Occasionally, microscopic wrinkles called striae (pronounced stri'-e) can occur in the flap after LASIK surgery.  If these wrinkles are significant enough to affect visual acuity, the surgeon may have to lift the flap (immediately or several days after surgery) and re-position it on the cornea. 

The cause of striae is usually unknown.  They appear to be more common when LASIK is performed on eyes that are very nearsighted.  It's possible that striae may occur from rubbing the eyes before the flap has securely bonded to the underlying cornea.  For this reason, LASIK patients are instructed to avoid rubbing their eyes for several weeks after surgery.

One study suggests the incidence of visually-significant striae is less than 1 percent.²

Epithelial Ingrowth

Epithelial ingrowth is a LASIK complication in which cells from the surface of the cornea (epithelial cells) begin to grow underneath the flap.

Epithelial ingrowth appears to occur in less than one percent of LASIK procedures.  A study of 589 eyes by Knorz et. al. noted that peripheral epithelial ingrowth occurred in 4 cases (0.6%).⁶ 

However, the incidence of epithelial ingrowth appears to be higher after enhancement LASIK procedures.  According to a study published by Drs. Wang and Maloney, the incidence of clinically significant epithelial ingrowth (defined as epithelial ingrowth which required surgical removal) was 0.92% after primary LASIK treatments (35 in 3,786 eyes) and 1.7% after enhancements (8 in 480 eyes).⁷

Most epithelial ingrowth is self-limiting and doesn't affect visual acuity.  In these cases, no treatment is required.  But in less than 10 percent of cases, the epithelial cells will continue to grow and interfere with vision.  In these cases, the surgeon will lift the flap, remove the epithelial cells and treat the area under the flap to decrease the likelihood of a recurrence.  A bandage contact lens may be placed on the eye for a few days to help the flap reattach securely.

Though epithelial ingrowth may occur as early as 1 or 2 days following LASIK surgery, it most often appears 1 to 3 months after surgery.  For this reason, it's important for LASIK patients to return to their doctor's office for follow-up exams for at least three months after LASIK.

According to the Wang and Maloney study, clinically significant epithelial ingrowth recurred in 10 of 43 affected eyes (23%) after the initial surgical removal.⁷

Other Potential Complications

Other potential complications after LASIK surgery include:

Diffuse lamellar keratitis (DLK)

Diffuse lamellar keratitis is a relatively rare post-operative complication of LASIK that is characterized by an accumulation of inflammatory cells under the corneal flap.  It has been nicknamed "Sands of the Sahara" because when viewed with a microscope it has the appearance of wind-blown sand dunes. 

Mild forms of DLK have been estimated to occur in 1% of LASIK procedures; severe cases comprise only about 1 in 5,000 surgeries.¹⁸   When it occurs, DLK usually appears at one to three days after LASIK.  The cause of DLK remains unknown.

There are no symptoms of early-stage DLK.  If it is detected early, the inflammation associated with DLK is easy to treat with medicated eye drops.  Failure to detect DLK in its early stages, however, could lead to vision loss.  (This is another reason why it is important for all patients to attend all of their LASIK follow-up exams as directed.)

Infection

The risk of eye infections related to LASIK surgery is minimal.  You will be given an antibiotic eye drop medicine to use for approximately one week after LASIK to prevent infection during the early stage of healing.

Sub-Conjunctival Hemorrhage

Occasionally, the suction that's applied to the eye to keep the microkeratome in place during the creation of the corneal flap will cause one or more small blood vessels to break on the white part of the eye ( the sclera).  The sclera is covered by a thin, clear membrane called the conjunctiva.  Hence, when a blood vessel breaks under the conjunctiva, it's called a sub-conjunctival hemorrhage.

The broken blood vessels will seal on their own, but for a period of time the leaking blood will fan out under the conjunctiva to create a bright red spot on the sclera.  Sub-conjunctival hemorrhages can be very small in size or they can cover the entire "white" of the eye. 

Though they can look scary, sub-conjunctival hemorrhages pose no risk to vision and will not affect the healing of the cornea after LASIK.  It can take several weeks, however, for the blood to clear from the eye and the sclera to return to its normal appearance.

Summary

We hope this information will help you make an informed decision when considering LASIK.  We encourage you to visit a refractive surgeon of your choice to more fully discuss the risks and potential complications of LASIK as they pertain to your particular situation.

EyeTopics.com reviews the latest issues of major eye and refractive surgery journals to bring you up-to-date information regarding LASIK and other forms of refractive surgery.  Be sure to check back often for the most current information.

References

Wherever possible, eyeTopics provides references to studies cited in our articles in case you want to read these research reports in their entirety.  Please be aware that  many of these reports are published in professional journals and are written for eye care professionals, not a lay audience.

¹ Vidaurri-Leal, JS. Complications in 5000 LASIK procedures. Refractive Surgery 1998 Reshaping the Future, a publication of American Academy of Ophthalmology Subspecialty Day 1998 - Refractive Surgery; 61-64.

² Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. American Journal of Ophthalmology 1999: 127(2) 129-136.

³ Ambrosio, R, Wilson, SE. Complications of Laser in situ Keratomileusis: Etiology, Prevention, and Treatment. J Refract Surg 17, May/June 2001.

⁴ US FDA "Summary of Safety & Effectiveness Data" associated with PreMarket Approvals for Alcon LADARVision, Bausch & Lomb Technolas 217; Nidek EC-5000 and VISX Star 2 excimer lasers. Accessed from US FDA LASIK website http://www.fda.gov/cdrh/lasik/lasers.htm on January 7, 2005.

⁵ Casebeer JC, Kezirian GM. The CRS LASIK Study Summary of PMA Data. Presentation at American Society of Cataract and Refractive Surgery Annual Meeting, April, 1999.

⁶ Knorz MC, Jendritzer B, Hugger P, Liermann A. Complications of laser in situ keratomileusis (LASIK). Ophthalmologe 1999 Aug; 96(8): 503-8.

⁷ Wang MY Maloney RK. Epithelial ingrowth after laser in situ keratomileusis. Am J Ophthalmol 2000; 129:746-751.

⁸ Perez-Santonja JJ, Skalka HF, Alio JL. Contrast sensitivity after laser in situ keratomileusis. J Cataract Refract Surg. 1998; 24:183-189.

⁹ Holliday JT, Dedeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing and corneal topography. J Cataract Refract Surg. 1999; 25: 664-669.

¹⁰ Boxer-Wachler BS, Durrie DS, Assil KK, Krueger RR. Role of clearance and treatment zones in contrast sensitivity: Significance in refractive surgery. J Cataract Refract Surg. 1999; 25: 16-23.

¹¹ Mutyala S, McDonald MB, Scheinblum KA, Ostrick MD, Brint SF, Thompson H. Contrast sensitivity evaluation after laser in situ keratomileusis. Ophthalmology 2000 Oct;107(10):1864-7.

¹² Knorz MC, Huger P, Jendritzka B, Liermann A. Twilight visual acuity after correction of Myopia with LASIK. Ophthalmologe 1999 Nov;96(11):711-6.

¹³ Montes-Mico R, Charman WN. Choice of spatial frequency for contrast sensitivity evaluation after corneal refractive surgery. J Refract Surg 2001 Nov-Dec;17(6):646-51.

¹⁴ Cardona Ausina C, Perez Santonja JJ, Ayala Espinsoa MJ, Claramonte Meseguer P, Artola Riog A, Alio JL. Contrast sensitivity after laser in situ keratomileusis for myopia (LASIK-M). Arch Soc Esp Oftalmol 2000 Aug;75(8):541-6.

¹⁵ Wilson SE. Laser in situ keratomileusis-induced (presumed) neurotrophic epitheliopathy. Ophthalmology 2001 Jun;108(6):1082-7.

¹⁶ Benitez-del-Castillo JM, del Rio T, Iradier T, Hernandez JL, Castillo A, Garcia-Sanchez J. Decrease in tear secretion and corneal sensitivity after laser in situ keratomileusis. Cornea 2001 Jan;20(1):30-2.

¹⁷ Yu EY, Leung A, Rao S, Lam DS. Effect of laser in situ keratomileusis on tear stability. Ophthalmology 2000 Dec;107(12):2131-5.

¹⁸ Steinert, RF. Swami, AU. Diffuse Interface Keratitis. Review of Refractive Surgery, January 2000 46-52.