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   Table of Contents      
ORIGINAL ARTICLE
Year : 2000  |  Volume : 48  |  Issue : 3  |  Page : 209-12

Partial flap during laser In-situ Keratomileusis: Pathogenesis and timing of retreatment


Medical and Vision Research Foundations, Chennai, India

Correspondence Address:
S K Rao
Medical and Vision Research Foundations, Chennai
India
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Source of Support: None, Conflict of Interest: None


PMID: 11217252

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  Abstract 

Purpose: To report the timing of retreatment and clinical outcomes in patients with a partial corneal flap during laser in-situ keratomileusis (LASIK), and to describe the causes of this complication.
Methods: Retrospective review of case records of four patients (4 eyes) who had a partial corneal flap during LASIK.
Results: The mean age of the four patients was 23 ± 4.7 years, and mean preoperative spherical equivalent (SE) refraction was -9.1 ± 3.1D (range, -5.5 to -13D). A 160 μm corneal flap was attempted during the initial treatment. Retreatment with a 180 μm corneal flap was performed at a mean of 5.1 ± 1.6 weeks (range, 4 to 7.5 weeks) after the initial procedure. There were no intraoperative complications during retreatment. Post-LASIK mean SE refraction was -1.0 ± 1.1D (range, +0.38 to -2.0D), after a mean follow up of 19 ± 15.7 weeks (range, 7 to 42 weeks). Best spectacle-corrected visual acuity decreased in one eye from 6/5 to 6/6 and was maintained in the others.
Conclusion: LASIK retreatment can be performed as early as one month after a partial flap, if the refraction is stable and a thicker corneal flap is created.

Keywords: Adult, Comparative Study, Cornea, pathology, surgery, Corneal Diseases, etiology, pathology, surgery, Disease Progression, Female, Humans,


How to cite this article:
Rao S K, Padmanabhan P, Sitalakshmi G, Rajagopal R. Partial flap during laser In-situ Keratomileusis: Pathogenesis and timing of retreatment. Indian J Ophthalmol 2000;48:209

How to cite this URL:
Rao S K, Padmanabhan P, Sitalakshmi G, Rajagopal R. Partial flap during laser In-situ Keratomileusis: Pathogenesis and timing of retreatment. Indian J Ophthalmol [serial online] 2000 [cited 2020 Aug 5];48:209. Available from: http://www.ijo.in/text.asp?2000/48/3/209/14873

POSTOP. UVA - POSTOPERATIVE UNAIDED VISUAL ACUITY; POSTOP. BSCVA - POSTOPERATIVE BEST SPECTACLE-CORRECTED VISUAL ACUITY

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POSTOP. UVA - POSTOPERATIVE UNAIDED VISUAL ACUITY; POSTOP. BSCVA - POSTOPERATIVE BEST SPECTACLE-CORRECTED VISUAL ACUITY

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BSCVA - BEST SPECTACLE-CORRECTED VISUAL ACUITY

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BSCVA - BEST SPECTACLE-CORRECTED VISUAL ACUITY

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Rapid, painless recovery of vision and reduced subepithelial haze are important advantages of laser insitu keratomileusis (LASIK), and result from the creation of a corneal flap which preserves the central Bowman's layer and epithelium.[1] The use of a lamellar microkeratome to create the flap is however, associated with a definite learning curve,[2] and flap-related complications are reported in 5.0 to 8.7% of cases undergoing LASIK.[3] A partial corneal flap, due to the microkeratome head not completing its full excursion, has been reported in up to 3.0% of cases.[2] If the hinge of the partial flap interferes with laser ablation of the stromal bed, postponement of the procedure is recommended.[4] Although previous studies have suggested retreatment of such eyes 2-3 months after the initial procedure, [1,3-6] the ideal time to repeat LASIK is still not clear. We describe this complication in four patients, report the outcomes after early retreatment and discuss the aetiopathogenesis of a partial flap.


  Materials and Methods Top


The case records of 508 consecutive patients who underwent LASIK at our institute from December 1997 to June 1999 were reviewed retrospectively. Four patients (4 eyes) had a partial flap during LASIK. These four procedures were performed between July 1998 and March 1999. Data obtained from the case records included preoperative refraction and best spectacle-corrected visual acuity (BSCVA), dates of initial and subsequent LASIK treatment, and unaided visual acuity (UVA), refraction, BSCVA and slitlamp biomicroscopic findings at the last follow-up visit.

All procedures were performed using the same automated microkeratome (HansatomeR, Chiron Corp, Irvine, California). A 160 μm corneal flap was planned in all the procedures. Suction was maintained during the procedure in patients # 1,2 and 3. The assistant inadvertently stepped on the vacuum footswitch during creation of the flap in patient # 4, resulting in loss of suction and a partial flap. Laser ablation was abandoned in all patients when a partial flap was noted. The stromal surface was cleaned and the flap was reposited. The edges of the flap and the bed were aligned precisely using the previously placed corneal marks as guides. A rigid eye shield was placed over the operated eye till the next morning. All patients were examined the next day. After slitlamp biomicroscopy revealed a well apposed corneal flap, patients were treated with 0.3% ciprofloxacin (CiploxRR, Glaxo, Mumbai, India) and tear substitutes (Tears PlusR, Allergan, Bangalore, India) eye drops, four times daily for the next one week. The topical steroid was tapered gradually in the next three weeks, and the tear substitute was continued at the same frequency for one month.

During retreatment, a 180 μm corneal flap was fashioned using the Chiron HansatomeR, and laser ablation was performed using the Summit SVS Apex Plus excimer laser (Summit Technologies, Waltham, Massachusetts).


  Results Top


The clinical characteristics of the four patients are described in [Table - 1]. Post-LASIK results and outcomes in the fellow eyes are described in [Table - 2]. The mean age of the four patients (3 males, 1 female) was 23 ± 4.7 years. Mean preoperative SE refraction was -9.1 ± 3.1D. The average time interval before retreatment was 5.1 ± 1.6 weeks. Mean SE refraction after LASIK was -1.0 ± 1.1D, after a mean follow up of 19 ± 15.7 weeks. Postoperative BSCVA decreased from 6/5 to 6/6 in one eye (Patient # 3), and was maintained in the other eyes. There were no intraoperative complications during retreatment.


  Discussion Top


Intraoperative flap-related complications can result in visual loss, if managed inappropriately.[5] In patients with a short or partial flap during LASIK, management depends on the extent of the uncut flap and location of the hinge of the reflected flap. If the reflected flap hinge is at the periphery of the planned treatment zone, the flap hinge can be shielded with a moist sponge during laser ablation. This can however, result in flattening and irregular astigmatism adjacent to the hinge, probably due to a tethering effect of the hinge on the adjacent cornea.[4] Decreasing the size of the treatment zone may also be considered, to protect the hinge, but visual results are often unsatisfactory if the patient's scotopic pupil size is larger than the ablation zone. Manual dissection of the flap to its full extent using lamellar dissection is an option, but can result in irregular astigmatism.[4] If the hinge is in the central 5-6 mm of the cornea, the best option is to reposition the flap and postpone laser ablation.

A 2-3 month delay before retreatment, in eyes with a partial flap, has been suggested in previous studies. [1,3-6] The basis for this recommendation is however, not clear. Experience with LASIK enhancement has indicated that the corneal flap can be dissected from the stromal bed with relative ease, up to 9 months after the initial procedure.[7] Thus, complete flap healing is unlikely in the time interval suggested for retreatment. While a longer delay will increase the safety of retreatment, this is often unacceptable to the patient, especially if the other eye has received LASIK resulting in anisometropia.

Our patients were all young adults keen to have retreatment, to permit them to return to work or studies as early as possible. Refraction was repeated prior to retreatment in patients # 2, # 3 and # 4 and was similar to the preoperative values. Slitlamp biomicroscopy showed a well-apposed corneal flap in all eyes. We therefore performed retreatment within two months of the initial procedure. We used a 180 μm corneal flap during the retreatment. We did not experience any intraoperative problems. Postoperatively, the healing response and refractive outcomes were not different from the fellow eye that underwent uneventful LASIK (Table 2). Patient # 2 had an induced astigmatism of 4 diopters after retreatment. Since retreatment was performed in this patient after stabilization of refraction 7.5 weeks after the initial attempt (the longest interval among the 4 patients), we do not think it is related to the timing of the procedure. This patient had the highest preoperative myopia (-13.0D), and had the deepest laser ablation. It is possible that this may have contributed to the induced astigmatism.

Pallikaris et al,[8] described flap healing in six human blind eyes, following the creation of a 300 μm corneal flap. The flaps were replaced without laser ablation of the stromal bed. Serial pachymetry in these eyes revealed a return of central corneal thickness to preoperative values within one month. Even with the 300 (μm corneal flap, the values remained stable after one month. Computerized videokeratography revealed a regular corneal surface topography, five weeks after surgery. Thus, the corneal flap in LASIK appears to be sufficiently stable to allow retreatment with a thicker flap, one month after the initial procedure.

Reasons postulated for an incomplete pass of the microkeratome include inadequate exposure of the globe due to interference by the eyelid, speculum and or drape, and loss of suction during the procedure.[9] A tendency for this complication to occur more often in the second eye of a patient during simultaneous bilateral LASIK has been described.[10] This has been attributed to crystal formation in the gears or suction ring of the microkeratome, from the balanced salt solution used during the first procedure. A decline in the incidence of an incomplete pass rate with increase in surgeon's experience,[9] suggests that this complication often occurs due to faulty surgical technique.

The first three cases in our series occurred during three treatment sessions performed between 24 July 1998 and 10 August 1998. There was no intraoperative loss of suction or mechanical obstruction of the moving parts of the microkeratome in any patient. We do not perform simultaneous, bilateral LASIK, and therefore the instrument was disassembled, autoclaved and reassembled before each procedure. Crystal formation in the gears of the microkeratome is therefore, an unlikely possibility. The problem occurred with different surgeons, all of whom were experienced refractive surgeons. These factors and the temporal clustering of the three cases within a 2-week period caused us to suspect microkeratome malfunction. The problem in the microkeratome was confirmed as "galling". This term refers to metal-to-metal transfer caused by the frictional hot spots created by a combination of pressure, lack of sufficient lubrication and speed. A defective blade that is too thick or has a high spot (surface flaw) causes galling in the microkeratome head. This results in increased resistance during blade oscillation and can cause incomplete excursion of the microkeratome. We routinely inspect microkeratome blades under the operating microscope prior to instrument assembly and did not detect any flaws in the blades used for these patients. Further discussions with the instrument supplier indicated that smooth, resistance-free sliding of the blade in its microkeratome housing must be ensured during microkeratome assembly to avoid galling. Regular servicing of the instrument at half yearly intervals is also recommended to avoid this problem.

The partial flap in patient # 4 was due to an inadvertent release of vacuum during surgery, caused by assistant error. Since the Hansatome ceases to cut on loss of suction during the procedure, a partial flap was produced. We have now designed a protective housing for the footswitch to prevent inadvertent activation of the vacuum footswitch during the creation of a corneal flap.

In conclusion, our results indicate that retreatment after a partial flap during LASIK, can be safely performed as early as one month after the initial procedure. It is however, important to ensure a stable refraction and a well-healed corneal flap, and to use a thicker corneal flap during retreatment. In patients with a thin cornea and or high myopia, in whom a 180 μm flap is considered inappropriate, it may be prudent to wait for a longer period. Our experience also indicates that all cases of partial flap are not necessarily due to surgeon error and reemphasizes the importance of thoroughly understanding the instrumentation used in LASIK



 
  References Top

1.
el Danasoury MA, el Maghraby A, Klyce SD, Mehrez K. Comparison of photorefractive keratectomy with excimer laser in situ keratomileusis in correcting low myopia (from -2.00 to -5.50 diopters) - A randomized study. Ophthalmology 1999;106:411-21.  Back to cited text no. 1
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2.
Farah SG, Azar DT, Gurdal C, Wong J. Laser in situ keratomileusis: Literature review of a developing technique. J Cataract Refract Surg 1998;24:989-1006.  Back to cited text no. 2
[PUBMED]    
3.
Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am J Ophthalmol 1999; 127:129-36.  Back to cited text no. 3
[PUBMED]  [FULLTEXT]  
4.
Wilson SE. LASIK: Management of common complications. Cornea 1998; 17:459-67.  Back to cited text no. 4
[PUBMED]  [FULLTEXT]  
5.
Stulting RD, Carr JD, Thompson KP, Waring GO III, Wiley MM, Walker JG. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999;106:13-20.  Back to cited text no. 5
    
6.
Gimbel HV. Flap complications of lamellar refractive surgery (Editorial). Am J Ophthalmol 1999;127:202-4.  Back to cited text no. 6
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7.
Durrie DS, Aziz AA. Lift-flap retreatment after laser in situ keratomileusis. J Refract Surg 1999;15:150-3.  Back to cited text no. 7
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8.
Pallikaris IG, Papatzanaki ME, Siganos DS, Tsilimbaris MK. A corneal flap technique for laser in situ keratomileusis - Human studies. Arch Ophthalmol 1991;145:1699-1702.  Back to cited text no. 8
    
9.
Gimbel HV, Penno EEA, 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;105:1839-47.  Back to cited text no. 9
    
10.
Clinch TE. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. (Discussion). Ophthalmology 1999;105:1847-48.  Back to cited text no. 10
    



 
 
    Tables

  [Table - 1], [Table - 2]


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