Barraquer et al described keratomileusis for the first time in 1961, which worked by eliminating central stromal tissue.1 In 1983, Trokel et al described the use of excimer lasers in refractive surgery.2 Initially, the excimer laser was used for surface ablation techniques, such as photorefractive keratectomy (PRK).2 Years later, this technique was combined with the cutting of a hinged lamellar flap on the anterior part of the cornea, using a specialized device called a microkeratome. The photoablation of the stromal tissue under the flap was performed to change corneal curvature, leading to a new technique called laser in situ keratomileusis (LASIK).3
Today, LASIK is the most common method used worldwide for correcting refractive errors. A critical step in this surgery is the flap creation with the microkeratome. Many different complications are associated with flap creation in LASIK.4'5 This study evaluated the incidence of intraoperative complications when using the NIDEK MK-2000 microkeratome (NIDEK, Gamagori, Japan) during flap creation.
PATIENTS AND METHODS
All complications that occurred during flap creation in LASIK using the NIDEK MK-2000 microkeratome between May 2000 and September 2004 in five outpatient refractive surgery centers in Mexico were retrospectively studied. Seven surgeons performed the procedures using the exact same methods. The number of eyes operated on by each surgeon ranged from 1800 to 15,000.
All of the procedures were primary LASIK surgeries. Only the surgical complications that occurred during flap creation were identified. All of the surgical procedures were performed with a standard technique. All surgeons were trained previously on the use and assembly of this microkeratome. Trained staff at each center inspected all parts including the blade before assembly of the keratome. A specialized technician, as recommended by the manufacturer, serviced all microkeratomes used in this study. Approximately 90% of cases were performed as simultaneous bilateral LASIK, using the same blade in both eyes. Suction was monitored using the incorporated suction gauge in the microkeratome console.
Complications During Flap Creation in LASIK Using the NIDEK MK-2000 Microkeratome
All intraoperative complications related to the creation of the flap were reviewed and classified in one of the following five categories: 1) incomplete pass; 2) irregular flap; 3) free cap; 4) buttonhole; and 5) epithelial abrasion.
Between May 2000 and September 2004, a total of 26,600 primary LASIK procedures were performed. Sixty-five complications were identified in the same period (Table). When an intraoperative complication occurred in the first eye, the second eye was not treated on the same day. All complicated cases in the series had a complication in only one eye.
Chart analysis of all cases revealed that the most common complication was a free flap in 23 (0.086%) eyes, followed by incomplete pass in 13 (0.049%) eyes, epithelial abrasion in 13 (0.049%) eyes, buttonhole in 11 (0.041%) eyes, and an irregular flap in 5 (0.019%) eyes. A total of 26,535 (99.756%) eyes had uneventful surgery.
Flap hinge length and flap diameter are correlated to the corneal mean keratometric power and thickness. The NIDEK MK-2000 microkeratome creates a predictable flap thickness. When compared to the Hansatome (Bausch & Lomb, Rochester, NY) and Chiron Automated Corneal Shaper microkeratomes (Chiron, Claremont, Calif), the MK-2000 has a smaller deviation from the intended flap thickness.67
In an incomplete pass, various etiologies have been postulated, including incomplete exposure of the globe, physical interference of the eyelid, drapes or speculum, and also inadequate suction.
This retrospective analysis on the incidence of complications during flap creation using the NIDEK MK-2000 microkeratome in 26,600 cases of primary LASIK surgeries revealed that complications are rare. It is well documented that LASIK offers some advantages over PRK including less pain, a shorter visual recovery time, and faster refractive stability.48 Nevertheless, the creation of the flap may be associated with the risk of flap complications.35 These complications include free flaps, buttonholes, irregular flaps, epithelial abrasions, incomplete passes, loss of suction, clinically thin flaps, and anterior chamber perforations. These complications can lead to the loss of best corrected visual acuity.5 Fortunately, in our group, complications such as suction loss, clinically thin flaps (except for some of the free caps), or anterior chamber perforation did not occur.
In our study, we found that the incidence of these complications using the NIDEK MK-2000 microkeratome is one of the lowest in the industry (0.244%), but still represents a disadvantage for LASIK surgery compared to surface ablation procedures.9 This incidence is notably lower than other reports that analyzed intraoperative microkeratome complications using this and other microkeratomes.1014 In various studies, the incidence of intraoperative flap complications has been reported to range from 0.0078% to 19.8%. 7
The NIDEK MK-2000 microkeratome has some design characteristics that may contribute to a low incidence of complications when creating flaps; it has different ring sizes that allow eyes with different corneal curvatures and a wide variety of myopic, hyperopic, and mixed astigmatic ablations to be treated. Because of this, the risk of ablating the flap hinge is reduced.6 This keratome has no exposed gears, which prevents external blockage of translation, and has two steel bars that help prevent lids from interfering with its advancement during the cut. Lastly, this keratome is handed to the surgeon preassembled, which allows the surgery to be performed with one hand.
The low incidence of flap complications in this study may also be related to the fact that all of the data are from seven surgeons in different closed access facilities using only one type of microkeratome, which minimizes the number of variables in creating the flap.
The most common type of complication in our study was a free flap. Free flaps are associated with flat corneal curvature. In this study, we did not study the relationship of the incidence of complications to corneal curvature, suction ring diameter, or plate thickness.
This study demonstrated that use of the NIDEK MK-2000 microkeratome results in a low incidence of intraoperative flap complications during LASIK. It is a safe and reliable device for creating flaps during LASIK.
1. Barraquer JI. The history and evolution of keratomileusis. Int Ophthalmol Clin. 1996;36:1-7.
2. Pallikaris IG, Papatzanaki ME, Stathi EZ, Frenschock O, Georgiadis A. Laser in situ keratomileusis. Lasers Surg Med. 1990;10:463-468.
3. Bas AM, Onnis R. Excimer laser in situ keratomileusis for myopia. J Refract Surg. 1995;11:S229-S233.
4. Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am ? Ophthalmol. 1999;127:129-136.
5. Stulting RD, Carr JD, Thompson KP, Waring GO III, Wiley WM, Walker JG. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology. 1999;106:13-20.
6. Gimbel HV, Penno EE, Van Westenbrugge JA, Ferensowicz M, Furlong MT. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology. 1998;105:1839-1848.
7. Jacobs JM, Taravella MJ. Incidence of intraoperative flap complications in laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:23-28.
8. Kremer FB, Dufek M. Excimer laser in situ keratomileusis. J Refract Surg. 1995;11:S244-S247.
9. Davidorf JM, Zaldivar R, Oscherow S. Results and complications of laser in situ keratomileusis by experienced surgeons. J Refract Surg. 1998;14:114-122.
10. Gimbel HV, Basti S, Kaye GB, Ferensowicz M. Experience during the learning curve of laser in situ keratomileusis. J Cataract Refract Surg. 1996;22:542-550.
11. 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-S726.
12. Tham VM, Maloney RK. Microkeratome complications of laser in situ keratomileusis. Ophthalmology. 2000;107:920-924.
13. Pallikaris IG, Katsanevaki VJ, Panagopoulou SI. Laser in situ keratomileusis intraoperative complications using one type of microkeratome. Ophthalmology. 2002;109:57-63.
14. Walker MB, Wilson SE. Lower intraoperative flap complication rate with the Hansatome microkeratome compared to the automated corneal shaper. J Refract Surg. 2000;16:79-82.
Complications During Flap Creation in LASIK Using the NIDEK MK-2000 Microkeratome