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Middle East African Journal of Ophthalmology Middle East African Journal of Ophthalmology
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Year : 2010  |  Volume : 17  |  Issue : 1  |  Page : 56-59 Table of Contents     

Intraoperative and postoperative complications of laser in situ keratomileusis flap creation using intralase femtosecond laser and mechanical microkeratomes

1 Department of Ophthalmology, Tulane University, New Orleans, LA, USA
2 Department of Ophthalmology, North Carolina University, Chapel Hill, NC, USA

Date of Web Publication22-Mar-2010

Correspondence Address:
Ladan Espandar
Ophthalmology Department, Tulane University, 1430 Tulane Ave., 5th Floor, New Orleans, LA
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0974-9233.61217

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An essential step of laser in situ keratomileusis surgery is corneal flap creation, Femtosecond (FS)-assisted or mechanical microkeratome. Each type has rare intraoperative and postoperative complication rates. Several recent studies have identified risk factors and guidelines to help manage these complications. Fortunately, studies have shown no loss of best-corrected visual acuity (BCVA) after the management of intraoperative and postoperative complications in IntraLase FS and mechanical microkeratome. Refractive surgeons need to be aware of the types of complications that can occur, how to avoid them and how to manage them to ensure the best possible outcomes.

Keywords: IntraLase Femtosecond Microkeratome, Laser in situ Keratomileusis Flap, Mechanical Microkeratome

How to cite this article:
Espandar L, Meyer J. Intraoperative and postoperative complications of laser in situ keratomileusis flap creation using intralase femtosecond laser and mechanical microkeratomes. Middle East Afr J Ophthalmol 2010;17:56-9

How to cite this URL:
Espandar L, Meyer J. Intraoperative and postoperative complications of laser in situ keratomileusis flap creation using intralase femtosecond laser and mechanical microkeratomes. Middle East Afr J Ophthalmol [serial online] 2010 [cited 2021 Oct 18];17:56-9. Available from: http://www.meajo.org/text.asp?2010/17/1/56/61217

   Introduction Top

Laser in situ keratomileusis (LASIK) is currently the most popular refractive surgery procedure worldwide. A critical step of LASIK surgery is the creation of the corneal flap. The two most common ways to create the flap are with a femtosecond (FS) laser or mechanical microkeratome. In recent years, the IntraLase FS laser (IntraLase Corp., Santa Ana, CA, USA) has gained increasing popularity. [1] However, the majority of refractive surgeons are still using the mechanical microkeratome. The purpose of this review is to compare and contrast the various types and rates of complications when using these two methods of flap creation.

   Mechanical Microkeratome Top

The mechanical microkeratome uses shear force traveling across the corneal stroma with an oscillating blade to create a flap. Several types of mechanical microkeratomes are available, such as the Amadeus (Advanced Medical Optics, Santa Ana, CA, USA), Hansatome (Technolas Bausch and Lomb, Rochester, NY, USA), Summit-Krumeich-Barraquer (SKBM; Alcon, Ft Worth, TX, USA), Supratome (Schwind, Kleinostheim, Germany) and Automated Corneal Shaper (Chiron Vision Corp., Emeryville, CA, USA). The differences between the various models include the number of motors, single-handed versus double-handed keratome operation, flap diameter, flap thickness and cutting rate related to the oscillation rate of the knife motor.

Jacobs and Taravella, [2] in a retrospective analysis of 28,530 primary LASIK cases, reported a 0.302% total intraoperative complication rate using the Automated Corneal Shaper and Hansatome microkeratomes. Complications included failure to achieve the appropriate intraocular pressure (0.034%), partial flaps (0.099%), buttonholes (0.070%), thin or irregular flaps (0.087%) and free flaps (0.012%). The Hansatome microkeratome was associated with a lower complication rate (0.16%) than the Automated Corneal Shaper (6.38%) (P < 0.005).

Nakano et al. [3] also showed that different microkeratomes have statistically different intraoperative complication rates, with a higher rate seen in the Automated Corneal Shaper (1.26%) relative to the Hansatome and MK-2000 (Nidek Inc., Fremont, CA, USA) (0.63% each). Complications included incomplete flaps (0.23%), buttonholes (0.13%), thin flaps (0.08%) and free flaps (0.08%).

One main step in the prevention of flap complications is risk-factor identification and modification. Flap thickness created by the mechanical microkeratome can be a major variable according to some studies. Yau and Cheng [4] argued that even with the same microkeratome (Moria M2, Doylestown, PA, USA), blades from different manufacturers produce significantly different flap thickness. However, Alio and Penero [5] showed that the Moria M2 and Carrizo-Pendular (SCHWIND eye-tech-solutions, Kleinostheim, Germany) microkeratomes created predictable flap thickness, as measured by very-high frequency digital ultrasound.

Epithelial defect formation during LASIK using a mechanical microkeratome has been studied for risk factor association. One study found increasing patient age (especially over 40 years) and preoperative hyperopia as risk factors for epithelial defect formation with the Hansatome microkeratome. [6] Another review of 1,873 eyes that underwent LASIK with the Automated Corneal Shaper microkeratome showed that the risk of epithelial damage was associated with increasing age, years of contact lens wear and intraoperative epithelial damage in the first eye during simultaneous bilateral LASIK. [7]

Preoperative keratometric power has been found to affect intraoperative complications as well. From a review of 34,099 eyes, flatter corneas tended to have more free caps and incomplete flaps whereas eyes with steeper corneas tended to have more epithelial abrasions and thin or irregular flaps. [8] Preoperative risk assessment should not be limited to the cornea. Asano-Kato et al. [9] found that narrow palpebral fissures (common in Asian populations) might be a risk factor for insufficient fixation of a microkeratome.

   Intralase Femtosecond Laser Microkeratome Top

The IntraLase FS laser is a solid-state laser used to create corneal lamellar flaps by producing a circular cleavage plane starting at one side and progressing across the cornea in a back and forth pattern. It applies patterned pulses of ultrashort wavelength energy at many intrastromal points with a predetermined depth. Each laser pulse generates a small amount of microplasma, which results in microscopic gas bubbles in the interface and creates the flap. It creates a flap edge of a programmable angle by using a circumferential pattern of progressively shallower pulses. A predefined arc along the edge is left uncut to create the hinge. The entire process takes place through a glass applanation plate that is fixed to the eye with a low-pressure suction ring. Creation of a smooth optical interface has been the primary goal of flap production in order to have better optical quality, reduced aberrations and improved visual outcomes. Sarayaba et al., [10] in a cadaveric study, evaluated the stromal bed quality produced by the Hansatome microkeratome with a 160-µm head and IntraLase 15- and 30-kHz FS laser with 110 µm thickness by scanning electron microscopy. They found that the 30-kHz IntraLase created a smoother stromal bed compared with the 15-kHz and Hansatome due to a tighter spot/line separation and lower energy per pulse.

The accuracy of the LASIK flap thickness is a key risk factor for flap complications and ectasia following LASIK. Kezirian and Stonecipher, [11] in a retrospective study, showed that IntraLase produced a more predictable flap relative to a mechanical microkeratome as measured by a DGH Pachette 50/60 kHz pachymeter. Binder [12] showed predictability of flap thickness, flap diameter and hinge location, which eliminates the risk for cap perforations. Kim et al. [13] showed a highly reproducible flap thickness with IntraLase, as measured by optical coherence tomography (Visante, Carl Zeiss Meditec).

Several studies have compared the visual outcomes of LASIK using the IntraLase versus mechanical microkeratome for creation of the flap. Durrie and Kezirian [14] showed in a prospective contralateral-eye study that the IntraLase group had significantly better mean uncorrected visual acuity (UCVA), less residual astigmatism and fewer trefoils in aberrometry. However, Patel et al., [15] in a randomized, controlled, paired-eye study, reported 6% higher corneal backscatter (haziness examined by confocal microscopy) in IntraLase flaps relative to mechanical at 1 month, but not at 3 or 6 months postoperatively. No difference was found in high-contrast visual acuity and contrast sensitivity. Therefore, the method of flap creation did not affect visual outcomes in this study. In a more recent retrospective study of 2,000 eyes, the percentage of eyes that achieved an UCVA of 20/20 or better was significantly higher in the FS laser relative to mechanical microkeratome and a lower percentage of eyes in the FS laser group lost two or more lines of BSCVA postoperatively. [16]

Even though the IntraLase FS laser may offer several advantages compared to the mechanical microkeratome, complications with the FS laser have been reported in the literature. According to several published reports, the incidence of diffuse lamellar keratitis (DLK) is greater in eyes where the LASIK flap was created with a FS laser compared to those created with a mechanical microkeratome. [17],[18],[19] Gas breakthrough, [20] opaque bubble layer, [18] suction loss leading to incomplete flap [12] and transient light sensitivity syndrome (TLSS) [21] have also been reported with the use of the FS laser.

Haft et al., [22] in a retrospective, noncomparative, interventional case series, described intra- and postoperative complications of the IntraLase FS microkeratome in 4,772 eyes. They reported a total complication rate of 0.92%. Intraoperative (flap-related) complications developed in 0.25%, premature breakthrough of gas through the epithelium within the flap margins was seen in 0.17%, incomplete flap due to suction loss was found in 0.06% and one eye had an irregular flap due to a previous scar.

For premature breakthrough gas, no management was suggested and one might continue the procedure without further complications. For incomplete flaps, a second laser pass at the same level simultaneously might be performed without further complications. Postoperative complications comprised of TLSS in 0.25% and DLK (stage 1-2) in 0.42%, which was treated with an intensive course of topical steroids. Overall, none of the complications caused loss of BSCVA in any of the studied eyes.

Moshirfar et al., in an unpublished retrospective, interventional case series, compared the intra- and postoperative flap complication rate of the Hansatome microkeratome (896 eyes) with IntraLase FS60 laser (902 eyes). They found a 14.2% total complication rate in the Hansatome group relative to 15.2% in the IntraLase group (P = 0.5437). Intraoperative complications included major epithelial defect/sloughing, incomplete flap, buttonhole or vertical gas breakthrough (in the case of the FS laser), torn flap, severely decentered flap preventing ablation and gas bubble in the anterior chamber. Postoperative complications occurring within 6 weeks of the original procedure included dislocated flap, epithelial ingrowth (after original surgery without enhancement), DLK stages I-III, central toxic keratopathy and TLSS. The intraoperative flap complication rate was 5.3% for Hansatome and 2.9% for IntraLase ( P = 0.0111). The most common intraoperative complication in the Hansatome group was major epithelial defect/sloughing at a rate of 2.6%, which was significantly higher than the IntraLase group ( P = 0.0006).

When comparing buttonhole formation, those that occurred in the setting of the microkeratome were typically central and round and approximately 3-4 mm in diameter. The subepithelial gas breakthrough seen with the FS laser-created flap was often peripheral and 1-2 mm in diameter. Although gas breakthrough is not typically classified as a buttonhole, the end results were the same. The occurrence of buttonholes with the use of FS is rare, [20] and the lower incidence of buttonholes in the FS group could be due to the fact that FS laser creates a planar flap as opposed to the meniscus-shaped flap created by the microkeratome. [12],[23]

The incidence of torn flaps was similar in both the IntraLase (0.4%) and the Hansatome groups (0.4%). However, all flap tears in the IntraLase group occurred at the flap hinge as opposed to the more central Hansatome flap tears. An advantage of tearing at the hinge is the avoidance of the central axis and having the option of proceeding with stromal ablation the same day.

Decentered flaps have been reported as a complication with mechanical microkeratomes. A low number of flap dislocations with the FS laser are most likely due to the FS side cut's steeper angle and deeper gutter as well as the increased adhesion strength of the FS flap. [24]-[27]

The postoperative flap complication rate was 8.9% for Hansatome and 12.3% for IntraLase ( P = 0.0201). The most common postoperative complication was DLK in both groups, 6.0% with the Hansatome and 10.6% with IntraLase ( P = 0.0002). It has been hypothesized that accumulation of gas bubbles and the energy of the FS laser could lead to an increased inflammatory response in individuals who might be more susceptible to DLK. [17] Even though the IntraLase group had a higher incidence of DLK, the patients did not progress to DLK stage III, and DLK can often be managed with an intense course of topical corticosteroids.

Bubbles in the anterior chamber, TLSS and rainbow glare are complications unique to the FS laser. Two case reports found that anterior chamber bubbles can interfere with pupillary tracking, but are self-limiting and resolve over a short period of time. [28],[29] Patients with TLSS present approximately 2-6 weeks after uneventful LASIK with severe photosensitivity. [21] These patients have good UCVA and no inflammatory findings on slitlamp exam, and treatment with topical steroids has been found to be effective. Rainbow glare is an optical side-effect in which patients report seeing a spectrum of colored bands radiating from a white-light source when viewed in a dark environment, such as a night-time setting. [30] The exact cause of TLSS and rainbow is not known. For TLSS, it is theorized that increased energy of the FS laser can stimulate local keratocytes and/or corneal nerve endings. [21] Stonecipher et al. looked at different groups showing a TLSS incidence rate of 1.0-1.4%, and 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 TLSS was achieved. [21] Similar to TLSS, rainbow glare appears to occur more often with higher raster energy settings. [30]

It is noteworthy to mention that none of the studied patients with intraoperative or postoperative flap complications in IntraLase FS and mechanical microkeratome groups experienced loss of BSCVA after the management of complications.

   Conclusion Top

Microkeratome flap complications can occur with either mechanical or IntraLase FS laser created flaps. Fortunately, these complications are rare and several recent studies have identified risk factors and guidelines to help manage these complications. Prospective comparisons of mechanical and FS laser microkeratome in LASIK have shown no significant clinical differences in final visual acuity after the management of complications. Refractive surgeons need to be aware of the types of complications that can occur, how to avoid them and how to manage them to ensure the best possible outcomes. [31]

   References Top

1.Slade SG. The use of femtosecond laser in the customization of corneal flaps in laser in situ keratomileusis. Curr Opin Ophthalmol 2007;18:314-7.  Back to cited text no. 1      
2.Jacobs JM, Taravella MJ. Incidence of intraoperative flap complications in laser in situ keratomileusis. J Cataract Refract Surg 2002;28:23-8.  Back to cited text no. 2      
3.Nakano K, Nakano E, Oliveira M, Portellinha W, Alvarenga L. Intraoperative microkeratome complications in 47,094 laser in situ keratomileusis surgeries. J Refract Surg 2004;20: S723-6.  Back to cited text no. 3      
4.Yau CW, Cheng HC. Microkeratome blades and corneal flap thickness in LASIK. Ophthalmic Surg Lasers Imaging 2008;39:471-5.  Back to cited text no. 4      
5.Alio JL, Penero DP. Very high-frequency digital ultrasound measurement of the LASIK flap thickness profile using the Intralase femtosecond laser and M2 and Carriazo-Pendular microkeratomes. J Refract Surg 2008;24:12-23.  Back to cited text no. 5      
6.Randleman JB, Lynn MJ, Banning CS, Stulting RD. Risk factors for epithelial defect formation during laser in situ keratomileusis. J Cataract Refract Surg 2007;33:1738-43.  Back to cited text no. 6      
7.Chen YT, Tseng SH, Ma MC, Huang FC, Tsai YY. Corneal epithelial damage during LASIK: A review of 1873 eyes. J Refract Surg 2007;23:916-23.  Back to cited text no. 7      
8.Albelda-Valles JC, Martin-Reyes C, Ramos F, Beltran J, Llovet F, Baviera J. Effect of preoperative keratometric power on intraoperative complications in LASIK in 34,099 eyes. J Refract Surg 2007;23:592-7.  Back to cited text no. 8      
9.Asano-Kato N, Toda I, Hori-Komai Y, Takano Y, Tsubota K. Risk factors for insufficient fixation of microkeratome during laser in situ keratomileusis. J Refract Surg 2002;18:47-50.  Back to cited text no. 9      
10.Sarayba MA, Ignacio TS, Binder PS, Tran DB. Comparative study of stromal bed quality by using mechanical, IntraLase femtosecond laser 15- and 30-kHz microkeratomes. Cornea 2007;26:446-51.  Back to cited text no. 10      
11.Kezirian GM, Stonecipher KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. J Cataract Refract Surg 2004;30:804-11.  Back to cited text no. 11      
12.Binder PS. Flap dimensions created with the IntraLase FS laser. J Cataract Refract Surg 2004;30:26-32.  Back to cited text no. 12      
13.Kim JH, Lee D, Rhee KI. Flap thickness reproducibility in laser in situ keratomileusis with a femtosecond laser: Optical coherence tomography measurement. J Cataract Refract Surg 2008;34:132-6.  Back to cited text no. 13      
14.Durrie DS, Kezirian GM. Femtosecond laser versus mechanical keratome flaps in wavefront-guided laser in situ keratomileusis: Prospective contralateral eye study. J Cataract Refract Surg 2005;31:120-6.  Back to cited text no. 14      
15.Patel SV, Maguire LJ, McLaren JW, Hodge DO, Bourne WM. Femtosecond laser versus mechanical microkeratome for LASIK: A randomized controlled study. Ophthalmology 2007; 114:1482-90.  Back to cited text no. 15      
16.Tanna M, Schallhorn SC, Hettinger KA. Femtosecond laser versus mechanical microkeratome: A retrospective comparison of visual outcomes at 3 months. J Refract Surg 2009;25: S668-71.  Back to cited text no. 16      
17.Gil-Cazorla R, Teus MA, de Benito-Llopis L, Fuentes I. Incidence of diffuse lamellar keratitis after laser in situ keratomileusis associated with the IntraLase 15 kHz femtosecond laser and Moria M2 microkeratome. J Cataract Refract Surg 2008;34:28-31.  Back to cited text no. 17      
18.Chang JS. Complications of sub-Bowman's keratomileusis with a femtosecond laser in 3009 eyes. J Refract Surg 2008;24: S97-101.  Back to cited text no. 18      
19.Javaloy J, Vidal MT, Abdelrahman AM, Artola A, Alió JL. Confocal microscopy comparison of Intralase femtosecond laser and Moria M2 microkeratome in LASIK. J Refract Surg 2007;23:178-87.  Back to cited text no. 19      
20.Srinivasan S, Herzig S. Sub-epithelial gas breakthrough during femtosecond laser flap creation for LASIK. Br J Ophthalmol 2007;91:1373.  Back to cited text no. 20      
21.Stonecipher KG, Dishler JG, Ignacio TS, Binder PS. Transient light sensitivity after femtosecond laser flap creation: Clinical findings and management. J Cataract Refract Surg 2006;32:91-4.  Back to cited text no. 21      
22.Haft P, Yoo SH, Kymionis GD, Ide T, O'Brien TP, Culbertson WW. Complications of LASIK flaps made by the ntraLase 15- and 30 kHz femtosecond lasers. J Refract Surg 2009;25:979-84.  Back to cited text no. 22      
23.Stonecipher K, Ignacio TS, Stonecipher M. Advances in refractive surgery: Microkeratome and femtosecond laser flap creation in relation to safety, efficacy, predictability, and biomechanical stability. Curr Opin Ophthalmol 2006;17:368-72.  Back to cited text no. 23      
24.Soong HK, Malta JB. Femtosecond lasers in ophthalmology. Am J Ophthalmol 2009;147:189-97.  Back to cited text no. 24      
25.Kim JY, Kim MJ, Kim TI, Choi HJ, Pak JH, Tchah H. A femtosecond laser creates a stronger flap than a mechanical microkeratome. Invest Ophthalmol Vis Sci 2006;47:599-604.  Back to cited text no. 25      
26.Knorz MC, Vossmerbaeumer U. Comparison of flap adhesion strength using the Amadeus microkeratome and the IntraLase iFS femtosecond laser in rabbits. J Refract Surg 2008;24:875-8.  Back to cited text no. 26      
27.Kamburoglu G, Ertan A. Epithelial ingrowth after femtosecond laser-assisted in situ keratomileusis. Cornea 2008;27:1122-25.  Back to cited text no. 27      
28.Srinivasan S, Rootman DS. Anterior chamber gas bubble formation during femtosecond laser flap creation for LASIK. J Refract Surg 2007;23:828-30.  Back to cited text no. 28      
29.Lifshitz T, Levy J, Klemperer I, Levinger S. Anterior chamber gas bubbles after corneal flap creation with a femtosecond laser. J Cataract Refract Surg 2005;31:2227-9.  Back to cited text no. 29      
30.Bamba S, Rocha KM, Ramos-Esteban JC, Krueger RR. Incidence of rainbow glare after laser in situ keratomileusis flap creation with a 60 kHz femtosecond laser. J Cataract Refract Surg 2009;35:1082-6.  Back to cited text no. 30      
31.Lee JK, Nkyekyer EW, Chuck RS. Microkeratome complications. Curr Opin Ophthalmol 2009;20:260-3.  Back to cited text no. 31      


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