Because femtosecond laser technology is a relatively new development in the armamentarium of the refractive surgeon, relatively few studies examining the incidence of complications are available in the literature. Although these complications may be rare and usually do not affect final BSCVA, our study was able to elucidate the types of complications associated with femtosecond laser flap creation in LASIK and strategies to manage these complications. Complications of flap creation in femtosecond LASIK can be grouped into indirect and direct complications. The primary indirect complications are DLK and transient light sensitivity syndrome. Some of the more common direct complications include suction loss, epithelial breakthrough, gas bubbles in the anterior chamber, and irregular flaps.
Diffuse lamellar keratitis (ie, Sands of the Sahara) is a syndrome that can result in diffuse haze of the interface (Fig 1).13 Treatment includes topical steroids, oral steroids (in more severe cases), and lifting of the flap and irrigating the stromal bed with balanced salt solution. Binder16 reported moderate DLK in the first 20 (19.4%) eyes in a series of 103 eyes operated with the IntraLase 6-kHz femtosecond laser. Javaloy et al17 reported stage 1 to 3 DLK in 17 (17%) of 100 eyes using a 15-kHz femtosecond laser. Gil-Cazorla et al18 reported 5 cases of stage 2 to 3 DLK in 1000 eyes operated with the IntraLase 15-kHz laser. The lower incidence of DLK in the IntraLase group in that study may be explained by the more intense anti-inflammatory therapy (8 times daily in the femtosecond group instead of 4 times daily) during the first postoperative week.
Figure 1. Diffuse Lamellar Keratitis. Note the Typical Diffuse Inflammation and Granular, “sandy” Opacification (arrow).
Total laser energy imparted to the tissue may be an important factor in the pathogenesis of DLK. One of our cases of postoperative stromal inflammation (Fig 2) supports this theory. This case showed peripheral stromal haze at the edges of the flap cut, where the side-cut was performed with higher energy settings. In our study, 20 (0.42%) eyes developed DLK (stage 1 to 2) after LASIK. This occurred using the 15-kHz laser in 15 eyes and in 5 eyes with the 30-kHz laser. All patients had clinically evident DLK on postoperative day 1, and all were treated with an intensive course of steroids. No surgical intervention was needed (eg, flap lift). At 1-year follow-up, none of these patients had loss of BSCVA.
Figure 2. Focal Stromal Inflammation at the Flap Edge. Haze Is Primarily Seen at the Flap Edge (arrow), Likely Due to the Higher Laser Energy Settings Needed for the Side Cut.
Transient light sensitivity syndrome is a clinical condition characterized by unusual photosensitivity with normal visual acuity several weeks after otherwise uneventful LASIK with the femtosecond laser that typically responds to topical treatment with topical steroids or cyclosporine. Stonecipher et al14 reported a 1.1% rate of this complication in femtosecond LASIK (5667 total cases). These patients were treated with prednisolone acetate drops and one surgeon also used cyclosporine 0.05% ophthalmic solution. Patients noted improvement of symptoms within 1 week of treatment. Muñoz et al15 also reported transient light sensitivity syndrome after femtosecond laser–assisted LASIK. They reported a 1.3% incidence of transient light sensitivity, which decreased with aggressive use of postoperative topical steroids. Our study reports 12 (0.25%) eyes with transient light sensitivity syndrome (which occurred in 10 eyes with the 15-kHz laser and 2 eyes with the 30-kHz laser). It is theorized that higher energies used with previous femtosecond laser platforms (10 and 15 kHz) produce activated keratocytes and cause delayed return to their normal state, which may cause transient light sensitivity syndrome. Indeed, Stonecipher et al14 noted that when the raster and side-cut energy settings were lowered (by an average of 24% and 33%, respectively), a significant reduction in the incidence of transient light sensitivity syndrome was achieved. With the newer 60- and 150-kHz platforms, lower energy is delivered per pulse, which may result in a lower rate of transient light sensitivity syndrome in the future.
Suction loss may occur during laser flap creation, which can lead to an incomplete flap. Retreatment to complete the flap may be problematic because the original plane of cutting may not be found and a second interface may be created. Also, a thin, buttonholed, or irregular flap may be created. Improper technique in applying the suction ring to the eye can cause loss of suction. A study examining risk factors for loss of suction in microkeratome-assisted LASIK found other risk factors for inadequate fixation, including narrow palpebral fissures, flat corneas, and young age.19 Narrower palpebral fissures leave limited room to effectively apply the suction apparatus to the eye. Younger patients may have stiffer lids that do not open as easily with a lid speculum. Conjunctival chemosis at the limbus may also interfere with the suction ring, not allowing adequate suction to build. Conjunctival massage can be used to push fluid away from the limbus in the case of conjunctival edema from repeated suction attempts. In addition, a conjunctival incision can be used to drain fluid and lessen edema. Sometimes delaying the procedure for a few hours to a few days may be needed to allow the edema to resolve.20 Binder reported suction loss in 6 eyes of 1000 cases.7 In our study, the rate of suction loss was 0.06%. A second pass successfully managed incomplete flaps, which resulted in intact flaps as planned. All procedures were completed, and the eyes that were followed for at least 6 months had excellent visual and refractive results.
Epithelial breakthrough (Fig 3) during femtosecond laser flap creation has been reported and studied only recently and only a few cases are reported in the literature. Srinivasan and Herzig21 reported the first case of subepithelial gas breakthrough during femtosecond laser flap creation for LASIK. They proposed that thin flaps or a focal break in Bowman’s layer may contribute to vertical gas breakthrough. In our study, we report 8/4772 (0.17%) eyes with this type of complication. In a previous study,10 we proposed that for gas breakthrough, a focal area of altered epithelium and thinned stroma in the area of scarring creates a low-resistance pathway that allows the gas bubbles to escape toward the surface instead of through the typical lamellar plane. Regarding epithelial breaks during flap lifting (after the femtosecond laser–assisted flap was created), it may be that stromal scarring may trap gas bubbles and not allow advancement through the flap interface to allow completion of the flap. In addition, during flap lifting itself, stromal fibrosis may anchor the flap to the underlying bed and induce breakthrough and flap tears. For these reasons, femtosecond laser flap creation should be done with caution in patients with corneal scars. If possible, increasing flap thickness may allow the creation of a flap interface more posterior to the scars. Also, another option may be to increase the energy of the raster pass and/or decrease the spot and line separation. If scars are widespread and visualization of anterior chamber structures is difficult, femtosecond laser flap creation should be avoided.
Figure 3. Epithelial Breakthrough (arrows). A Low Resistance Pathway Through Altered Epithelium and Thinned Stroma in the Area of a Corneal Scar May Result in This Complication.
An irregular or decentered flap (Fig 4) may also occur during femtosecond laser flap creation. Irregular flaps can result from loss of suction. Patients with deep-set eyes, small corneas, or eyes with conjunctival edema can result in inadequate contact with the suction apparatus. Avoidance of cutting the flap when intraocular pressure is low (low suction) is an important precaution. Care should be taken in performing femtosecond LASIK in pseudophakic eyes that may be more susceptible to suction loss. Buttonhole flap formation, seen in steep corneas cut with microkeratomes, was not noted in our series. Buttonholes may occur in microkeratome cases due to buckling of the cornea at the applanation head, as well as proposed increased corneal resistance with upward movement of the cutting blade.20 With these types of complications (whether with microkeratome or femtosecond laser), the safest management may be to reposition the flap and abort the procedure. A deeper flap can typically be recut approximately 3 months later. In our study, this complication was found in three eyes. One eye had a LASIK procedure aborted due to irregular flap creation, and declined retreatment later. Despite this, the patient did not lose BSCVA.
Figure 4. Decentered Flap. The Shorter Arrow Points to the Flap Bed; the Longer Arrow Points to the Edge of the Excimer Laser Reticle, Which Is Centered over the Pupil.
Although the application of femtosecond technology in refractive surgery does not completely eliminate LASIK complications, it reduces the risk of flap-associated complications in comparison with microkeratomes. Microkeratomes have an incidence of overall complications that range from 0.24% to 14%.9,22–24 Microkeratomes have been unpredictable in the past with regard to epithelial defects and loose epithelium, but newer mechanical microkeratome designs have improved in this area, although they still have up to a 2.6% rate of epithelial complications.3 In addition, with growing concerns of corneal ectasia induced by refractive surgery, the thickness of the flap and its predictability have become of paramount importance. Microkeratomes can be variably predictable in their ability to produce consistent flap thicknesses,25,26 which is problematic if an unexpectedly thick flap is created. The femtosecond laser has demonstrated more predictable flap thickness than microkeratomes.3,4,27 Intraoperative pachymetry performed prior to flap lift can help the femtosecond laser operator detect an unusually thick or thin flap.28 In addition, the femtosecond laser creates a flap of more uniform thickness than microkeratomes, which helps treat and prevent higher order aberrations.29,30 The femtosecond laser has also shown better refractive and visual acuity outcomes when compared with traditional microkeratomes.3
Further improvements in femtosecond laser technology could further enhance LASIK outcomes. For example, the 60-kHz femtosecond laser platform allows for lower energy to be used for the lamellar flap creation. This lower energy may decrease the incidence of some of the indirect femtosecond–related complications reported here, such as DLK and transient light sensitivity syndrome.
Due to limitations in postoperative follow-up for our patients, we are unable to comment on the incidence of ectasia after LASIK in these cases with the femtosecond laser, although no patients developed ectasia to the best of our knowledge. There is also a lack of long-term studies in the literature quantifying the incidence of this complication in relation to femtosecond laser use. One can hypothesize that with more predictable flap thickness with the femtosecond laser, the incidence of ectasia after LASIK may be reduced.
Although femtosecond laser technology is not completely free of complications, it provides an attractive alternative to traditional microkeratomes. As with any new technology, there is heightened interest in performing studies to further determine the mechanisms that explain the complications. More studies are needed to help elucidate these mechanisms, as well as other potential advantages and disadvantages of the technology.