Risks and Complications
Like all surgical procedures, LASIK has some potential risks and complications. The incidence of refractive surgery patients having unresolved complications six months after surgery has been estimated from 3% to 6%.
The following information is intended to provide you with an understanding of some of the risks so that you can make an informed decision. Every patient should weigh the chance of experiencing complications against the potential benefits of refractive surgery. While we have done our best to provide you with an overview of some of the complications, every patient should fully review his or her situation with our optometrist so that the information can be understood in the context of each individual case.
Potential complications can be divided into three distinct categories: intraoperative, post operative, and quality of
Intra-operative complications are surgical complications that occur during the procedure itself.
- The incidence of flap complications has been estimated to be 0.244%. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries, but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience. According to proponents of such techniques, this risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches, although this is not proven and carries its own set of risks of
- A slipped flap (a corneal flap that detaches from the rest of the cornea) can occur. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep to let the flap heal. Patients are usually given sleep goggles or eye shields to wear for several nights to prevent them from dislodging the flap in their sleep. A faster operation may decrease the chance of this complication, as there is less time for the flap to dry.
- Flap interface particles are another finding whose clinical significance is undetermined. A Finnish study found that particles of various sizes and reflectivity were clinically visible in 38.7% of eyes examined via slit lamp.
Post-operative complications are complications associated with healing that occur after the patient leaves the operating room.
Overcorrection, Undercorrection, and Regression
Every eye heals differently. The surgical plan is based upon an average healing response. Patients who are either aggressive or slow healers may experience an under, or overcorrection.
In addition, the stroma (the thickest part of the cornea and where the laser ablation takes place) may experience some slight remodeling and/or the epithelium (the thinnest and outermost layer of the cornea) may thicken after refractive surgery. Either of these conditions might result in a slight loss of refractive surgical effect (regression) post-operatively. In general, the higher the correction undertaken, the more likely regression is to occur, and this is especially true for treatment of hyperopia greater than +5D. Regression can also occur when the refractive surgery procedure is performed pre-maturely on a young patient that has not reached a stabilized visual plateau.
In most cases, undercorrection (where the treatment is insufficient to yield the desired change in vision) and regression (where the surgical effect is lost during the healing process) can be treated with an enhancement procedure. An overcorrection of myopia may be corrected by performing a hyperopic LASIK enhancement, whereas a hyperopic overcorrection would in most cases be correctable via a myopic LASIK enhancement. However, eyes with very thin or steep corneas or high degrees of refractive errors may not be eligible for enhancements. Therefore, patients should be sure to speak with our optometrists about their potential eligibility for an enhancement
Diffuse Lamellar Keratitis (DLK)
Diffuse lamellar keratitis is a unique and relatively rare post-operative condition following refractive surgery. Non-severe forms have been estimated to occur in 1% of cases; severe cases comprise only about 1 in 5,000 surgeries. A number of names including Sands of the Sahara have been used to describe this condition, which is characterized by an accumulation of inflammatory cells under the flap. The condition usually appears at one to three days after LASIK. However, there have been recent reports of late onset DLK. Multiple causes have been hypothesized, but no single explanation accounts for all cases.
Patients should understand that at the early stages of the condition, they most likely will not experience symptoms they would be able to discern, and only upon examination by a doctor could this condition be detected. When caught early, the inflammation associated with DLK is easy to treat. Patients should be aware, however, that while approximately 80% of the condition will clear up within the first 24 to 48 hours, it could take several weeks until the condition completely subsides.
We emphasize that this condition can be treated without significant visual loss when it is detected and treated early. Therefore, it is imperative that all patients maintain our optometrist's recommended post-operative follow-up examination schedule.
Flap Folds, Wrinkles & Striae
Usually minor flap striae, or wrinkles in the flap after LASIK surgery, do not interfere with vision. In such cases of visually insignificant flap striae, surgical treatment is usually unnecessary. However, sometimes the striae are serious enough to decrease visual acuity. In such instances, intervention is necessary.
To remove the striae, a surgeon might lift the flap, irrigate beneath it and lay it back down in the proper position. In cases of persistent striae, sutures may be necessary.
According to one study that considered 1019 eyes, 11 eyes experienced folds in the flap that required repositioning because of poor vision. The mean postoperative time for repositioning was 6 days. In one eye, the folds persisted to the next day, so the flap was repositioned again and sutured.
There are a number of causes of striae. Sometimes, rubbing the eyelids before the flap has had a chance to bond can cause subtle wrinkles. Patients can reduce this risk by avoiding rubbing their eyes for several weeks after surgery. Sometimes, malposition of the flap (laying it down in a different position from where it was lifted) can cause striae. Sometimes, striae form without an apparent cause, and they seem more common in very high myopes than in other patient populations.
Epithelial ingrowth is a condition in which epithelial cells, which normally cover the surface of the cornea, grow beneath the flap.
One study of 1013 eyes demonstrated a 14.7% incidence rate, with 1.7% of eyes requiring surgical removal because it interfered with vision. Another study of 783 eyes noted only 3 eyes experienced this complication.
Most epithelial ingrowth does not affect vision and does not require treatment. In such cases, our optometrists will simply leave the ingrowth alone and monitor it at post-operative visits. However, in about 1-2% of cases, epithelial ingrowth occurs within the field of vision or affects an area wide enough to require surgical treatment or removal. Central visually significant epithelial ingrowth can appear as early as 1-2 days post-operatively. However, epithelial cells most often appear at 1-3 months post-operatively. Therefore, it is important that patients attend all follow-up visits with our optometrists, especially for the first 6 months post-operatively.
According to a study published by Drs. Wang and Maloney, the incidence of clinically significant epithelial ingrowth after LASIK (defined as epithelial ingrowth which required surgical removal) was 0.92% after primary treatment (35 in 3,786 eyes) and 1.7% after retreatment (8 in 480 eyes). Central visually significant epithelial ingrowth can appear as early as 1-2 days post-operatively. However, epithelial cells most often appear at 1-3 months post-operatively. Left unattended, the cells that characterize visually significant epithelial ingrowth can release enzymes that melt the flap, causing vision loss.
Sometimes our optometrists will prescribe eye drops to minimize the effects, and this protocol will be sufficient. However, at other times a more aggressive approach will be necessary. Removing the epithelial cells is a relatively simple procedure. The ophthalmologist would lift the flap, wipe the underside of the flap with a swab-like sponge, then lay the flap back down. In rare cases where the epithelial ingrowth persists despite such removals, the surgeon may need to use sutures to secure the flap down and ensure that ingrowth cannot occur. According to the Wang and Maloney study, clinically significant ingrowth recurred in 10 of 43 affected eyes after the initial surgical removal.
Quality of vision
Decreased Contrast Sensitivity, Night or Low-Light Vision
Contrast sensitivity deals with a patient's ability to discern images of varying shades from the background - in other words, how faded an image can be before it is indistinguishable from the background. Imagine driving in fog - the thicker the fog, the grayer all objects become and the more difficult to distinguish their features. Because contrast sensitivity is important to the quality of vision, several studies have been conducted over the last several years to determine the affect of LASIK on it. All noted a decrease in contrast sensitivity which lasted from one to six months post-operatively. However, all but one also noted a return to pre-operative function by the six-month visit.
Subjective reporting of decreased night vision has been noted widely, with descriptions and illustrations of the potential effects of glare, halos and starbursts on a patient's vision. As this complication can occur and it can adversely impact a person's activities, we strongly suggest you discuss this with our optometrists.
Dry Eyes and Severe Dry Eye
Patients need to be aware that it is not uncommon to experience some symptoms of dry eyes post-operatively, especially in the first few weeks as the majority of corneal healing takes place. Those patients who have a pre-existing dry eye condition need to be especially aware of the potential risks regarding LASIK and dry eyes.
As early as December 1999, doctors were paying attention to the possible connection between LASIK and dry eye. At the 1999 joint meeting of the American Academy of Ophthalmology and the Pan-American Association of Ophthalmology, Dr. Robert Maloney reported the results of a survey of 550 patients after LASIK. 40-50% noted experiencing dry eyes at some time of the day 3 months post-operatively. Dr. Richard Lindstrom noted that while the overall frequency of complications after LASIK is decreasing, the incidence of dry eye after LASIK is increasing. Dr. Roger Steinert supported Dr. Lindstrom's assertion and provided a possible explanation: patients seek LASIK precisely because they are contact lens intolerant, and such intolerance is often indicative of dry eye. Dr. Marguerite McDonald noted several other possible explanations for the increased frequency of this condition post-operatively:
- Use of post-operative steroids after LASIK may exacerbate pre-existing dry eye.
- Previous contact lens wear disrupts normal corneal physiology.
- Hormonal changes during menopause or birth control pills can cause dry eye.
- The surgery itself may cause dry eye by cutting the nerves of the central cornea or damaging cilia.
Patients need to be aware that they may have dry eye symptoms for several months following LASIK, even if they did not have symptoms or signs of dry eye prior to surgery. Those patients who have severe conditions pre-operatively need to be aware that, because surgery can exacerbate the symptoms, our optometrists may deem them ineligible for surgery.