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Traumatic Corneal Perforation With Epithelial Ingrowth After Laser In Situ Keratomileusis
Arch Ophthalmol. 2001;119:907-909.
INTRODUCTION
Laser in situ keratomileusis (LASIK) is a promising refractive surgical procedure for low to high myopia. Its advantages over photorefractive keratectomy (PRK) include prompt visual recovery, increased patient comfort, potential to correct high myopia, less postoperative haze and regression, and less postoperative need for corticosteroids. Most LASIK-related complications occur intraoperatively or early postoperatively. They include flap-related complications, corneal perforation, corneal infection, macular hemorrhage, interface deposits, epithelial ingrowth, and irregular astigmatism.1-4 LASIK is performed by creating a lamellar flap followed by excimer laser application. The force that the residual untreated cornea could resist decreases as a result of "thinner" stromal bed. Displacement of the lamellar flap following minor blunt trauma after LASIK has been described in the literature.5 We herein present a case of blunt ocular injury related to corneal perforation in association with traumatic cataract 10 months after successful bilateral LASIK surgery.
Report of a Case
A 26-year-old man was referred to our emergency department in November 1998 on account of right eye injury by a flying stone, sized 3x 1.5 cm2, while at work. He received myopic LASIK on both eyes 10 months before this accident. Preoperative refraction was -2.75 diopters (D) in the right eye and -2.25 D/-1.00 Dx 180° in the left eye, respectively. The preoperative corneal thickness and depth of stromal ablation were 541/30 µm in the right eye and 542/37 µm in the left. The corneal flaps were presumably 150 µm in both eyes. An examination 8 hours after injury revealed a 10-mm horizontal laceration wound across the stromal bed. The corneal flap was displaced but remained adhered to the bed at the hinge. It was intact except for a minimal nicking at the edge. Traumatic cataract was also noted, and his visual acuity was hand motion at 30 cm in the right eye. Primary repair of corneal perforation combined with lens aspiration was performed initially, followed by repositioning of the flap without suture.
Owing to poor adhesion of the flap, scraping of the interface with removal of epithelial sheet at the interface was performed 2 days later. The flap was secured with interrupted sutures at the end of surgery (Figure 1A). Penetrating keratoplasty with posterior chamber intraocular lens implantation was done 4 months later for residual corneal opacity. The graft was clear Figure 1B), and he regained a best spectacle corrected visual acuity of 20/20 eight months after surgery. No retinal breaks or detachment was found during regular fundus examinations. Histologic examination of the corneal button showed corneal epithelium at the flap and bed interface (Figure 1C).
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Figure 1. After scraping of both sides of the interface, several interrupted sutures were placed to secure the flap and the adjacent cornea (A). The hinge was intact (between arrows). Four months after injury, penetrating keratoplasty combined with posterior chamber intraocular lens implantation was performed. The graft was clear and best-corrected visual acuity was 20/20 eight months after surgery (B). Histologic (hematoxylin-eosin) staining of corneal button (original magnification x200) showed corneal epithelium (between arrowheads) at the flap and bed interface (C).
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Comment
In a previous study,6 stromal wound healing after LASIK occurred at the flap edge and was minimal compared with that in the PRK group. This may support in part the clinical observation that less corneal haze was noted after LASIK than after PRK as a result of less disorganized stromal collagen fibers from wound healing process.7
Accidental ocular trauma is not uncommon, particularly in the young, active, and working population. Because the young population tends to receive refractive procedures more frequently, blunt ocular trauma after refractive surgery may become a major concern. Campos et al8 found that porcine eyes receiving PRK appeared less predisposed to rupture due to blunt trauma than did porcine eyes that underwent refractive keratectomy. However, to our knowledge, there is currently no published comparative study on the ocular integrity after LASIK. Theoretically, the force that the cornea could resist is directly proportionate to the thickness of the residual untreated stroma after LASIK, ie, the thinner the thickness, the more vulnerable to blunt ocular injury it will be. According to Munnerlyn's formula, ablation depth in microns (µm) = [optical zone (mm)]2x diopters of myopia (D)/3. To prevent ectasia, a minimal residual stromal bed thickness of at least 250 µm was advocated.
In our case, a grossly intact flap after injury meant that the patient had experienced a shearing force at the junction between the flap and the corneal bed in addition to a perpendicular penetrating one. The shearing force separated the flap from the bed and the vertical force perforated the residual "thinner" cornea (Figure 2). Since the wound healing process after LASIK takes place mostly at the periphery of the flap, the corneal flap may thus separate easily from the bed when subjected to a shearing force. Based on the operative parameters in this patient and a simple equation in biomaterial science, compressive stress  = F/A (F indicates the external force applied; A, cross-sectional area of the residual bed in LASIK cases),9 we deduced that the cornea treated with LASIK bore a compressive stress of 2.25-fold of an intact one as a result of a decreased cross-sectional area, taking the external force F as constant.
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Figure 2. Diagram illustrating the external force (F) applied to the cornea. The force can be divided into 2 vectors. The horizontal vector (H) displaces the flap from underlying stroma and the vertical vector (V) perforates the "thinner" corneal bed. S indicates stone.
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In this patient, the epithelium at the interface most likely occurred after injury. Epithelial ingrowth may lead to diffuse interface opacity, poor wound adhesion, surface irregularity, and peripheral flap melting.10 In this case, scraping of both sides of the interface was performed 2 days after primary repair. This did not eradicate epithelium completely because of poor epithelial sealing at the interface periphery secondary to the irregularity in the stromal bed, which resulted from primary closure of the perforation.
In summary, we present a case of blunt trauma–related corneal perforation after LASIK. Although LASIK is a relatively safe and efficient refractive surgery, the combinations of lamellar flap, stromal ablation, and little wound healing seem to decrease corneal resistance to unexpected ocular injuries. In the future, setting up a biomechanical model to study the relationship between stress and corneal resistance after LASIK seems mandatory to provide guidelines for patients facing high-risk conditions.
AUTHOR INFORMATION
We thank K. H. Hou, PhD, and N. Z. Wang, PhD, for stimulating discussion.
Corresponding author and reprints: Shu-Wen Chang, MD, Department of Ophthalmology, Chang Gung Memorial Hospital, 5 Fu-Shin St, Kweishan 333, Taoyuan, Taiwan, Republic of China (e-mail: shuwenchang{at}cgmh.com.tw).
Chi-Chin Sun, MD;
Shu-Wen Chang, MD;
Ray R. F. Tsai, MD
Taoyuan, Taiwan
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SECTION EDITOR: W. RICHARD GREEN, MD
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