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 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
Postoperative complications are more frequent. Research 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 the 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 by 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).
The first step in the LASIK procedure is the creation of a flap on the 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).
Research 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 reposition the flap. LASIK can then be rescheduled a few months later, after the flap has healed.
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.
Post-operative complications are complications associated with healing that occur after the patient leaves the operating room. Studies 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- or over-correction of their refractive error (i.e. nearsightedness, farsightedness or astigmatism).
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 the corrective effect) of the immediate LASIK result over time. In general, the stronger your eyeglass prescription is prior to LASIK, the greater the risk that there may be some regression. This is especially true for the treatment of high amounts of farsightedness.
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 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 the 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, that 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 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 by 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.
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.
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 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 moderately 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.
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 reposition 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.
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%).
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).
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.
Other Potential Complications
Other potential complications after LASIK surgery include:
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. When it occurs, DLK usually appears 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.)
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.
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.
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.