Hyperguides

Ophthalmology / Refractive surgery

Intraoperative LASIK Complications: Thin Flaps and Buttonholes

Neda Shamie, MD
Article


Introduction

Buttonhole flaps (Slide 1), especially thin flaps, are one of the more common LASIK flap-related intraoperative complications encountered, with incidence ranging from 0.1% to 0.2% depending on surgeon experience.1-6 In addition to surgical expertise, other factors that may affect the incidence of this complication include inadequate suction, corneal anatomy, and microkeratome malfunction or defect.7,8

Slide 1

With loss of suction or lower than ideal intraocular pressures (IOPs) during the microkeratome pass, buckling of the central cornea can occur, resulting in thin or perforated buttonhole flaps (Slide 2). Avoidance of this can be accomplished by assuring an IOP of at least 65 mm Hg using a Barraquer tonometer or pneumotonometer, verifying from the patient that the vision has dimmed, or by observing dilatation of the pupil intraoperatively after placement of the suction ring.8 Patients with excessive vitreous syneresis or history of vitrectomy may be at increased risk due to the difficulty of maintaining high enough IOPs using the suction ring and should be counseled appropriately.9

Slide 2

Flap Complications

Corneal anatomy with corneal curvatures outside of the normal range also can predispose a patient to intraoperative flap complications. Corneas steeper than 46 D or with an irregular surface (those with a history of previous penetrating keratoplasty or scleral buckle) are at increased risk of developing buttonhole flaps or flaps with central thinning. As in the case of inadequate suction, this is thought to occur as a result of central corneal buckling during the microkeratome pass (Slide 1).9 With proper preoperative evaluation and planning, the surgeon can opt to use a thicker plate on steeper corneas, or simply avoid the lamellar cut and proceed with photorefractive keratectomy (PRK) instead.

Slide 1

Probably the most avoidable factor related to this complication is microkeratome malfunction and, especially, poor blade quality.10 Meticulous attention to cleaning, assembly, and preoperative assessment of the blade and the microkeratome system can help minimize intraoperative complications. Additionally, gently stabilizing the ring and avoiding significant manual torque of the cornea during the microkeratome pass can help avoid irregular and possibly perforated flaps.8

Laser Ablation

In the case when a buttonhole flap is created, a consensus exists that the surgeon should not proceed with laser ablation of the stromal bed and should instead replace the flap and abort further surgery until at least 3 months later when a new, thicker flap can be recut.8,9 In the case when a thin flap without a buttonhole is created, the decision to abort further surgery is not as clear. Ablation can be performed safely when the central flap appears to be of adequate thickness. Some have proposed converting to immediate transepithelial PRK after repositioning the defective flap.11 The relative merits of this approach and the possibility of increased risk of haze with PRK in this setting are not yet completely understood. Of concern in the case of both buttonhole flaps and thin flaps is the increased risk of epithelial ingrowth, irregular astigmatism, stromal scarring, and flap striae.7,8

Probably the most avoidable factor related to this complication is microkeratome malfunction and, especially, poor blade quality.10 Meticulous attention to cleaning, assembly, and preoperative assessment of the blade and the microkeratome system can help minimize intraoperative complications. Additionally, gently stabilizing the ring and avoiding significant manual torque of the cornea during the microkeratome pass can help avoid irregular and possibly perforated flaps.8

References

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  2. Gimbel HV, Basti S, Kay GB, Ferensowicz M. Experience during the learning curve of laser in situ keratomileusis. J Cataract Refract Surg. 1996;22:542-550.

  3. Bas AM, Onnis R. Excimer laser in situ keratomileusis for myopia. J Refract Surg. 1995;11:S229-S233.

  4. Marinho A, Pinto MC, Pinto R, et al. LASIK for high myopia. Ophthalmic Surg Laser. 1996;27:S517-S520.

  5. Stulting RD, Carr JD, Thompson KP, et al. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology. 1999;106:13-20.

  6. Lindstrom RL, Hardten DR, Chu YR. Laser in situ keratomileusis for the treatment of low, moderate and high myopia. Trans Am Ophthalmol Soc. 1997;95:285-306.

  7. Jacobs JM, Taravella MJ. Incidence of intraoperative flap complications in laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:23-28.

  8. Buratto L, Brint S. Complications of LASIK. In: Buratto L, Brint S. LASIK Surgical Techniques and Complications. 2nd ed. 2000:189-191.

  9. Gimbel HV, Penno EEA. Intraoperative Complications. In: Gimbel HV, Penno EEA. LASIK Complications: Prevention and Management. 2nd ed. 2001:66-69.

  10. Slade SG. Free Cap,Thin and Perforated Corneal Flaps. In: Machat JJ, ed. Excimer Laser Refractive Surgery:Practice and Principles. 1996.

  11. Jain VK, Abell TG, Bond WI, et al. Immediate transepithelial photorefractive keratectomy for treatment of laser in situ keratomileusis flap complications. J Refract Surg. 2002;18:109-112.