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Clinicopathologic Reports, Case Reports, and Small Case Series |

Refractive, Topographic, and Visual Effects of Flap Amputation Following Laser In Situ Keratomileusis FREE

Stephen D. McLeod, MD; Douglas Holsclaw, MD; Salena Lee, OD
Arch Ophthalmol. 2002;120(9):1213-1217. doi:.
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Published online

A review of complications associated with laser in situ keratomileusis (LASIK) indicates that most are directly attributable to the creation of a corneal flap.1,2 In their examination of 1000 consecutive cases of patients who had undergone LASIK, Gimbel and colleagues1 identified 32 intraoperative and 18 postoperative complications, most of which could be related to issues of flap anatomy, including incomplete passes, thin flaps, buttonholes, flap shrinkage and flap dislocation with subsequent development of striae, and epithelial ingrowth. Stulting and colleagues2 reported complications encountered in a series of 1062 cases of patients who had undergone LASIK, and identified 27 intraoperative and 40 postoperative complications, all of which were directly related to the corneal flap with the exception of 2 cases of keratitis.

Although most complications can be resolved with acceptable visual outcomes, persistent flap irregularity or opacification will result in decreased vision. Since epithelialization of the underlying stromal bed might provide a more regular surface, amputation of the offending flap might be considered a reasonable intervention to address persistent flap problems. It is therefore important to understand the healing pattern of the corneal bed following flap creation and excimer laser ablation in terms of lens power, topography, regularity, and scar formation. In our experience, most cases of flap amputation have followed infectious keratitis and flap melting that results in some degree of scarring and opacification of the underlying corneal bed. Consequently, it has been difficult to predict what the optical qualities of the uninflamed stromal bed might have been. We document herein the corneal findings in 2 patients who underwent early flap amputation for noninflammatory epithelial ingrowth following LASIK.

Case 1

A 46-year-old woman with a history of recurrent corneal erosion and an examination finding consistent with map-dot-fingerprint dystrophy underwent bilateral LASIK for the correction of an error of –6.75 + 0.50 × 100 OD and –7.00 + 0.25 × 072 OS. An automated microkeratome (Automated Corneal Shaper [ACS]; Bausch & Lomb Surgical, Rochester, NY) was used to create the corneal flaps with nasally located hinges, followed by ablation with an excimer laser (VISX Star; VISX, Inc, Santa Clara, Calif). An epithelial defect was produced during surgery in the left eye. A bandage soft contact lens was placed, but a defect persisted at the first follow-up visit 1 day later. Approximately 3 weeks later, epithelial ingrowth along the interface of the corneal flap and the bed was identified at the hinge and extended toward the entrance pupil. The flap was elevated and the interface epithelium, removed. Approximately 2 weeks later, the epithelial ingrowth had recurred, so the flap was amputated.

The patient was treated with a bandage contact lens, and ciprofloxacin hydrochloride solution was applied every 3 hours. No corticosteroids were applied. During the next 5 days, the epithelial defect created by removal of the flap closed, the bandage contact lens was removed, and the patient was prescribed diclofenac sodium solution for occasional use up to 3 times daily and artificial tears for lubrication. Approximately 1 week after closure of the epithelial defect, the uncorrected visual acuity in the left eye was 20/100. Automated refraction identified an error of –5.50 + 3.50 × 159, but the corresponding visual acuity was not recorded. Topical corticosteroids were prescribed for application 3 times daily and discontinued after 1 month. During the next 6 months, the corneal haze in the left eye was not recorded as being any greater than 1+. However, at 9 months after flap amputation, the uncorrected vision was recorded as 20/100, correcting to 20/40 with a refraction of –1.50 + 0.25 × 171.

The patient was referred to the University of California, San Francisco Refractive Surgery Service for further consultation in May 2001, approximately 2 years after LASIK and flap amputation of the left eye. At that time, she complained of fluctuating vision in the left eye that at its best remained blurred. She also reported ghosting and glare. Examination disclosed an uncorrected visual acuity of 20/25 OD and 20/80 OS. The vision of the left eye improved to 20/25 with a refraction of –3.25 + 3.25 × 70.

Slitlamp biomicroscopic examination of the right eye showed a well-positioned, nasally hinged corneal flap, but coarse, diffuse epitheliopathy. There was no evidence of subepithelial or stromal haze or scarring, except for a normal degree of scar formation outlining the edges of the corneal flap. Slitlamp examination of the left eye showed a subtle, vertically oriented elevation of the corneal surface at the hinge of the amputated flap. There was no evidence of subepithelial or stromal scarring, either at the former location of the flap edge or over the central cornea. However, there was a moderate degree of epithelial irregularity evident without instillation of fluorescein sodium dye. Fluorescein sodium staining revealed coarse, diffuse epitheliopathy concentrated over the central cornea and an area of irregular surface contour that appeared to involve the central area of corneal dissection that produced the amputated flap.

Computerized corneal mapping (Figure 1) confirmed the relative irregularity of the left eye. A topographic map of the right eye (Tomey Topographic Modeling System, version 2.3.6J; Tomey Corp, Waltham, Mass) showed a simulated keratometry reading of 40.01 × 41.07@91° with a surface regularity index of 0.52 and a surface asymmetry index of 0.18. However, a topographic map of the left eye produced a simulated keratometry reading of 40.90 × 42.51@103° with a surface regularity index of 0.50 and a surface asymmetry index of 1.25. On comparing the right and left eyes, a markedly asymmetrical reflex was also observed on retinoscopy with significantly greater irregularity noted in the left eye.

Place holder to copy figure label and caption
Figure 1.

Case 1. Corneal topography of both eyes. Although the overall powers of the central corneal curvatures are similar, the left eye shows greater irregularity, as represented by the elevated surface asymmetry index (SAI). SimK indicates simulated keratometry; MinK, minimum keratometry; PVA, predicted visual acuity; CYL, cylinder; and SRI, surface regularity index.

Graphic Jump Location

Although a relatively high degree of astigmatism was noted in the left eye, the spherical equivalent was calculated to be –1.625 diopters (D). Since the refraction in the right eye was –1.50 + 1.00 × 090, anisometropia was limited, so spectacles were prescribed to improve visual function.

Case 2

A 33-year-old man underwent bilateral LASIK for the correction of an error of –1.75 + 0.50 × 30 OD and –2.00 + 0.25 × 160 OS. An automated microkeratome (ACS; Bausch & Lomb Surgical) was used to create the corneal flaps. A large epithelial defect was created in the left eye, so the flap was repositioned without excimer laser ablation. A bandage contact lens was placed to promote epithelial healing. Approximately 2 months later, the patient returned to surgery. A corneal flap with a nasal hinge was created in the left cornea using an automated microkeratome (ACS; Bausch & Lomb Surgical), and the ablation was performed using an excimer laser. An epithelial defect was noted at the end of the procedure, and a bandage contact lens was kept in place for the next 3 days. One week after surgery, uncorrected vision was 20/40 OS, correcting to 20/25 with a refraction of –1.00 + 1.50 × 20. No significant epithelial ingrowth was noted.

Two weeks later, the patient returned with the complaint of ocular discomfort in the left eye. Uncorrected vision was 20/30−. Epithelial ingrowth was noted along the nasal hinge, with extension toward the entrance pupil. At that visit, the flap was lifted to remove the interface epithelium, and the epithelium overlying the flap was noted to be friable. On the basis of anticipated difficulties with recurrent epithelial ingrowth, the flap was amputated and a bandage contact lens was placed. Ciprofloxacin and diclofenac solutions were prescribed 4 times daily. The epithelial defect healed during the next few days, and 1 week after flap amputation the uncorrected visual acuity was 20/200, correcting to 20/60 with a refraction of –5.00 + 1.50 × 100. The ciprofloxacin solution was discontinued, and corticosteroid drops were prescribed for use 3 times daily. Two months later, the uncorrected vision was 20/100, correcting to 20/50− with a refraction of –4.75 + 2.00 × 105. The corticosteroid therapy was reduced to 1 drop per day and then discontinued.

The patient complained of poor vision and nighttime glare and halo and was referred to the University of California, San Francisco Refractive Surgery Service for consultation in May 2001, approximately 18 months after LASIK and subsequent flap amputation of the left eye. Examination at that time disclosed an uncorrected visual acuity of 20/25 OD, correcting to 20/20 with a refraction of –0.50 + 0.50 × 55, and an uncorrected visual acuity of 20/60 OS, correcting to 20/20− with a refraction of –3.75 + 3.75 × 97. Pachymetry readings were 532 µm OD and 439 µm OS.

Slitlamp biomicroscopic examination of the right eye showed a well-positioned, nasally hinged corneal flap with mild central subepithelial opacification, whereas slitlamp examination of the left eye was remarkable for mild vertical linear elevation at the site of the transected hinge, a semicircle of subepithelial haze reminiscent of surface photorefractive keratectomy (PRK)–associated scarring that appeared to outline the perimeter of the flap, and a relatively lucent central cornea overlying the entrance pupil. (Figure 2) The surface of the central cornea appeared to be relatively smooth, but upon instillation of fluorescein sodium solution, inspection of the tear film pattern indicated an irregular surface.

Place holder to copy figure label and caption
Figure 2.

Case 2. Slitlamp photograph of the left eye. Note within the slit beam a band of scarring that outlines the perimeter of the flap, but relative clearing of the central cornea overlying the entrance pupil.

Graphic Jump Location

The irregularity of the left eye's corneal surface was confirmed by computerized corneal mapping (Figure 3). A topographic map of the right eye produced a simulated keratometry reading of 42.27 × 43.32@84°, with a surface regularity index of 0.11 and a surface asymmetry index of 0.50. However, a topographic map of the left eye showed a simulated keratometry reading of 43.57 × 46.40@115°, with a surface regularity index of 1.62 and a surface asymmetry index of 0.86. On comparing the right and left eyes, a markedly asymmetrical reflex was also observed on retinoscopy, with markedly greater irregularity noted in the left eye.

Place holder to copy figure label and caption
Figure 3.

Case 2. Corneal topography of both eyes. The left eye shows significant astigmatism with the rule and elevated irregularity compared with the right eye, as represented by elevated surface regularity (SRI) and surface asymmetry indices (SAI). Other abbreviations are explained in the legend to Figure 1.

Graphic Jump Location

Since the acuity in the left eye could be corrected to 20/20− with a relatively low degree of anisometropia based on spherical equivalent, spectacles were recommended, but the patient adamantly refused to consider spectacle correction. Rigid contact lenses were also suggested, but the patient elected to forgo fitting.

The findings from large reported series of complications seen in consecutive cases of patients who have undergone LASIK suggest that most complications can be attributed to abnormalities of the corneal flap that translate to irregularity or opacification of the anterior cornea.1,2 If amputation of the corneal flap were followed by reepithelialization and smoothing of the corneal surface (analogous to corneal healing after surface PRK) without the introduction of significant scarring, refractive error, or irregularity, then this approach might prove useful in addressing most postsurgical complications of LASIK. Unfortunately, few reports in the literature provide a guide to the clinical course that can be expected after flap amputation in the uninfected cornea. Patel and colleagues3 recently reported a case of traumatic flap dislocation that was followed by loss of the flap. After healing of the stromal bed, the patient's uncorrected vision was 20/40, improving to 20/20 with a refraction of –1.00 + 1.00 × 135.

However, as our 2 cases demonstrate, it cannot be assumed that a regular surface will result after removal of the flap. The irregular myopic astigmatism we observed implies that the curvature of the stromal bed might not precisely reflect that of the anterior surface of the overlying flap. This finding suggests that the flap might vary in thickness from one region to another, leading to variability in the curvature of the stromal bed created. Patterns of variability in thickness may well differ from one microkeratome to another, and this variability is expected to contribute to the development of irregularity in the contour of the stromal bed, which results in irregular astigmatism that limits best spectacle-corrected vision.

Under normal circumstances, irregularity of the surface of the stromal bed is expected to be matched by corresponding irregularity of the undersurface of the flap, so that if an irregular flap is created and then replaced precisely with a "lock and key" effect, little change on the anterior corneal surface is expected. If a regular refractive ablation is performed on the exposed stromal bed, some degree of underlying irregularity should be translated through the ablation so that as the surfaces are reapposed precisely, matching the bed to the underside of the flap, the composite effect on the surface of the eye should be attenuation of the irregularity. As our 2 cases suggest, this attenuating effect is lost if the flap is removed to expose the stromal bed.

Over time, remodeling of the epithelium might have a smoothing effect on the exposed stromal bed, improving best spectacle-corrected visual acuity. After this improvement, residual regular spherocylindrical error can be corrected with spectacles, hydrophilic contact lenses, or a standard spherocylindrical excimer laser treatment. In a topographic examination of eyes treated with excimer laser, Abbas and colleagues4 have demonstrated that significant corneal smoothing occurs from 3 months to 12 months after PRK, presumably as a result of stromal healing and remodeling. Using very high-frequency ultrasound scanning, Reinstein and colleagues5 examined corneas that had undergone LASIK and reported regional variations in epithelial thickness that tended to compensate for underlying stromal irregularity, thereby reducing corneal irregularity. In the 2 cases we present, it is discouraging that reduced best spectacle-corrected visual acuity with correspondingly elevated indices of asymmetry and irregularity was evident 18 months and 2 years after flap amputation. Therefore, it is questionable how much further improvement in surface regularity might occur during subsequent months or years.

In neither case was there substantial scarring of the corneal stroma overlying the entrance pupil that was subjected to excimer ablation. High degrees of refractive error corrected by surface PRK are expected to be associated with a greater risk of scarring, and it has been suggested that this scarring is related to the depth of the ablation performed.6 However, after flap amputation, relatively deep layers of the cornea were exposed to the epithelium after healing, and no significant haze was recorded throughout the healing period. This finding suggests that the risk for haze formation in PRK probably goes beyond simple considerations of exposure of the deeper stroma devoid of Bowman membrane to healing epithelium. Rather, these cases suggest that flap amputation is not necessarily followed by significant central corneal haze and scarring.

Nevertheless, the refractive and topographic outcomes of our 2 patients indicate that there is a substantial risk for refractive change and induction of irregular astigmatism following flap amputation. Any characteristic pattern of induced astigmatism is probably related to the path followed by the microkeratome in creating the flap, which in turn will be related to the particular design of the microkeratome. Since there were no other flap-related abnormalities beyond epithelial ingrowth in these cases, we surmise that flap amputation was performed because it was seen as a definitive treatment of the ingrowth that would produce acceptable surface smoothing over time.

The first patient we describe had a history of recurrent erosion syndrome, which presents an increased risk for epithelial ingrowth, keratolysis, flap melting, and loss of best corrected visual acuity.7 For this reason, LASIK is not recommended in the setting of anterior basement membrane disease, and PRK should be considered. Such severe complications might indeed ultimately necessitate flap amputation, but no such progression was seen in the cases reported herein. Therefore, based on the observed long-term clinical course, we suggest that in the absence of compelling indications (such as gross flap irregularities or interface infection in which the flap might limit antibiotics penetration), flap amputation should be a last resort in the management of flap complications.

Corresponding author: Stephen D. McLeod, MD, Department of Ophthalmology, University of California San Francisco, 10 Kirkham St, K-301, San Francisco, CA 94143 (e-mail: smcleod@itsa.ucsf.edu).

Gimbel  HVPenno  EEvan Westenbrugge  JAFerensowicz  MFurlong  MT Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology. 1998;1051839- 1847
Stulting  RDCarr  JDThompson  KPWaring 3rd  GOWiley  WMWalker  JG Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology. 1999;10613- 20
Patel  CKHanson  RMcDonald  BCox  N Late dislocation of a LASIK flap caused by a fingernail. Arch Ophthalmol. 2001;119447- 449[published correction appears in Arch Ophthalmol. 2002;120:180]
Abbas  ULHersh  PSSummit PRK Study Group, Late natural history of corneal topography after excimer laser photorefractive keratectomy. Ophthalmology. 2001;108953- 959
Reinstein  DZSilverman  RHSutton  HFColeman  DJ Very high-frequency ultrasound corneal analysis identifies anatomic correlates of optical complications of lamellar refractive surgery: anatomic diagnosis in lamellar surgery. Ophthalmology. 1999;106474- 482
Moller-Pedersen  TCavanagh  HDPetroll  WMJester  JV Corneal haze development after PRK is regulated by volume of stromal tissue removed. Cornea. 1998;17627- 639
Dastgheib  KAClinch  TEManche  EEHersh  PRamsey  J Sloughing of corneal epithelium and wound healing complications associated with laser in situ keratomileusis in patients with epithelial basement membrane dystrophy. Am J Ophthalmol. 2000;130297- 303

Figures

Place holder to copy figure label and caption
Figure 1.

Case 1. Corneal topography of both eyes. Although the overall powers of the central corneal curvatures are similar, the left eye shows greater irregularity, as represented by the elevated surface asymmetry index (SAI). SimK indicates simulated keratometry; MinK, minimum keratometry; PVA, predicted visual acuity; CYL, cylinder; and SRI, surface regularity index.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

Case 2. Slitlamp photograph of the left eye. Note within the slit beam a band of scarring that outlines the perimeter of the flap, but relative clearing of the central cornea overlying the entrance pupil.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 3.

Case 2. Corneal topography of both eyes. The left eye shows significant astigmatism with the rule and elevated irregularity compared with the right eye, as represented by elevated surface regularity (SRI) and surface asymmetry indices (SAI). Other abbreviations are explained in the legend to Figure 1.

Graphic Jump Location

Tables

References

Gimbel  HVPenno  EEvan Westenbrugge  JAFerensowicz  MFurlong  MT Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology. 1998;1051839- 1847
Stulting  RDCarr  JDThompson  KPWaring 3rd  GOWiley  WMWalker  JG Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology. 1999;10613- 20
Patel  CKHanson  RMcDonald  BCox  N Late dislocation of a LASIK flap caused by a fingernail. Arch Ophthalmol. 2001;119447- 449[published correction appears in Arch Ophthalmol. 2002;120:180]
Abbas  ULHersh  PSSummit PRK Study Group, Late natural history of corneal topography after excimer laser photorefractive keratectomy. Ophthalmology. 2001;108953- 959
Reinstein  DZSilverman  RHSutton  HFColeman  DJ Very high-frequency ultrasound corneal analysis identifies anatomic correlates of optical complications of lamellar refractive surgery: anatomic diagnosis in lamellar surgery. Ophthalmology. 1999;106474- 482
Moller-Pedersen  TCavanagh  HDPetroll  WMJester  JV Corneal haze development after PRK is regulated by volume of stromal tissue removed. Cornea. 1998;17627- 639
Dastgheib  KAClinch  TEManche  EEHersh  PRamsey  J Sloughing of corneal epithelium and wound healing complications associated with laser in situ keratomileusis in patients with epithelial basement membrane dystrophy. Am J Ophthalmol. 2000;130297- 303

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