Journal of Refractive Surgery

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Original Articles 

Recutting the Cornea Versus Lifting the Flap: Comparison of Two Enhancement Techniques Following Laser in situ Keratomileusis

Yuval Domniz, MD; Ian F Comaish, FRCOphth; Michael A Lawless, MD; Christopher M Rogers, MD; Gerard L Sutton, MD

Abstract

ABSTRACT

PURPOSE: To evaluate enhancement techniques following laser in situ keratomileusis (LASIK).

METHODS: Recutting was performed on 263 eyes and the flap was lifted in 55 eyes that had LASIK for simple myopia or myopic astigmatism. The time interval between LASIK and retreatment was 340 ± 46 days (range, 270 to 892 days) in the recutting group and 215 ± 36 days (range, 53 to 617 days) in the flap lifting group. Mean spherical equivalent refraction, refractive cylinder, uncorrected and best spectacle-corrected visual acuity were examined prior to, and 1, 3, and 6 months after retreatment.

RESULTS: Seventeen eyes were lost to follow-up in the lifting group and 53 eyes in the recutting group. In the recutting group, mean spherical equivalent refraction improved from -1.48 ± 1.25 D to -0.49 ± 0.88 D at 6 months. In the flap lifting group, mean spherical equivalent refraction improved from -1.05 ± 1.49 D to -0.45 ± 0.39 D at 6 months. Refractive cylinder did not change significantly in either group (P = .2). There was a significant increase in uncorrected visual acuity (UCVA) of 6/6 in each group. In the recutting group, UCVA of 6/6 increased from 3.8% to 65.2% at 6 months, and in the lifting group from 3.6% to 71.1% at 6 months. In the recutting group, seven free flaps and three macerated flaps that required removal occurred. One eye in the recutting group and two in the lifting group developed significant epithelial ingrowth. No patient lost more than one line of best spectacle-corrected visual acuity (BSCVA).

CONCLUSION: Both procedures were safe, effective, and highly predictable for enhancements, but flap complications may be more likely with recutting. [J Refract Surg 2001;17:505-510]

Abstract

ABSTRACT

PURPOSE: To evaluate enhancement techniques following laser in situ keratomileusis (LASIK).

METHODS: Recutting was performed on 263 eyes and the flap was lifted in 55 eyes that had LASIK for simple myopia or myopic astigmatism. The time interval between LASIK and retreatment was 340 ± 46 days (range, 270 to 892 days) in the recutting group and 215 ± 36 days (range, 53 to 617 days) in the flap lifting group. Mean spherical equivalent refraction, refractive cylinder, uncorrected and best spectacle-corrected visual acuity were examined prior to, and 1, 3, and 6 months after retreatment.

RESULTS: Seventeen eyes were lost to follow-up in the lifting group and 53 eyes in the recutting group. In the recutting group, mean spherical equivalent refraction improved from -1.48 ± 1.25 D to -0.49 ± 0.88 D at 6 months. In the flap lifting group, mean spherical equivalent refraction improved from -1.05 ± 1.49 D to -0.45 ± 0.39 D at 6 months. Refractive cylinder did not change significantly in either group (P = .2). There was a significant increase in uncorrected visual acuity (UCVA) of 6/6 in each group. In the recutting group, UCVA of 6/6 increased from 3.8% to 65.2% at 6 months, and in the lifting group from 3.6% to 71.1% at 6 months. In the recutting group, seven free flaps and three macerated flaps that required removal occurred. One eye in the recutting group and two in the lifting group developed significant epithelial ingrowth. No patient lost more than one line of best spectacle-corrected visual acuity (BSCVA).

CONCLUSION: Both procedures were safe, effective, and highly predictable for enhancements, but flap complications may be more likely with recutting. [J Refract Surg 2001;17:505-510]

Laser in situ keratomileusis (LASIK) has become the preferred surgical technique for the correction of myopia. Fast visual rehabilitation, minimal postoperative discomfort, and the ability to correct high amounts of myopia are the advantages this procedure holds over PRK.1"3 Additional strengths are mild postoperative haze and high predictability. Epithelial hyperplasia is associated with, and probably the main cause of, regression after LASIK4, and overall, undercorrection is the most common problem following LASIK. a Undercorrection and regression have been reported, especially in high myopia.' ß Studies have shown the effectiveness and predictability of LASIK retreatment using different techniques.6"8 We compared the results of recutting the cornea and lifting the original flap for enhancement treatment in myopia and astigmatic myopia.

PATIENTS AND METHODS

Of 5200 eyes that had LASIK performed at the Eye Institute for correction of myopia and myopic astigmatism between 1996 and 1999, 318 eyes underwent enhancement, because patients were unsatisfied with the achieved uncorrected visual acuity following LASIK. The 318 eyes fell into two groups; Group 1 included 263 eyes (82.7%) that underwent enhancement by recutting the cornea and Group 2 included 55 eyes (17.3%) that underwent enhancement by lifting the flap. Recutting was performed when the flap edge could not be easily identified. An abnormal flap was not the primary consideration in choosing the recutting procedure for enhancement. AU patients underwent a complete ophthalmic examination including measurement of uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), manifest and cycloplegic refraction, corneal topography, slit-lamp microscopy, Goldman applanation tonometry, funduscopy, keratometry, and pachymetry. The treatment was intended to leave remaining stromal thickness greater than 250 µm under the flap with each technique. None of the eyes displayed evidence of progressive corneal ectasia according to pachymetry, corneal topography, and refraction that remained stable for at least 2 months prior to the enhancement treatment. Postoperative examinations were conducted at 1 week, 1, 3, and 6 months, and as necessary after that. All primary LASIK procedures were performed using the Chiron Automated Corneal Shaper microkeratome (Bausch & Lomb, Rochester, NY) or Summit Krumeich Barraquer Microkeratome (SKBM, Alcon, Ft. Worth, TX). The LASIK flap diameter ranged between 6.9 and 9.00 mm and 160 µm thickness. The ablation was performed using the Summit Apex Plus Laser 193-nm excimer laser (Alcon, Ft. Worth, TX) at a fluence of 180 mJ/cmp 2 and a repetition rate of 10 Hz, using a multizone algorithm to a zone of 6.5 mm. Following ablation, the flap was replaced; no damage to the flap was observed in any of the eyes. No intraoperative or postoperative complications were observed during the primary procedure.

Three surgeons at our Institute performed the enhancement treatments. LASIK retreatment was performed using one of two methods: lifting the flap or recutting the cornea. The Apex plus laser was used for all eyes and a multizone ablation pattern, as well as a pretreatment program to prevent central island formation, was used routinely in all eyes. When lifting, the flap edges were marked with a needle to delineate the edge and cut through the epithelium. The patient was then aligned underneath the surgical microscope and the cornea was marked on the temporal side with gentian violet. A spreader was then inserted at the interface, as indicated by the demarcated flap edge. Once the flap interface was identified, the spreader was passed along the flap edge and the interface was dissected. The hinged flap was lifted using non-toothed forceps and placed against the nasal sclera. Laser ablation was then performed. The stromal bed was irrigated and the flap returned to its original position. After a few minutes, the flap was checked for adhesion using a blinking test.

The recutting method was performed at the same depth as the original cut. The technique used to perform the second cut was the same as the initial LASIK procedure, that is, with a nasal hinge and a 160-µm flap depth. A new blade was used in each eye and the microkeratome and blade checked prior to each procedure. The cornea was marked, a suction ring applied, and intraocular pressure verified as being greater than 65 mmHg. The automatic microkeratome was advanced along the track across the cornea, the suction ceased, and the ring was removed. Laser ablation was performed and the flap was re-positioned after irrigation of the stromal bed. Topical ofloxacin 0.3% and prednisolone acetate 1% were applied and flap position was verified by a blink test, 3 minutes and then 30 minutes following the procedure.

Data were compared statistically using the paired ¿-test. AP-value of less than .05 was considered statistically significant.

RESULTS

In Group 1 (recutting group), mean preoperative spherical equivalent refraction was -1.48 ± 1.25 D. In Group 2 (flap lifting group), mean preoperative spherical equivalent refraction was -1.05 ± 1.49 D. The time interval from the initial procedure to the enhancement in the recutting group was 340 ± 46 days (range, 270 to 892 days). The time interval from the initial procedure to the enhancement in the flap lifting group was 215 ± 36 days (range, 53 to 617 days). Mean patient age was 42.4 ± 5.6 years (range, 23 to 57 yr) in the recutting group and 39.9 ± 4.5 years (range, 23 to 55 yr) in the flap lifting group. In the recutting group, 51.1% of patients were male and in the flap lifting group, 50.3% were male. Seventeen eyes in the flap lifting group and 53 eyes in the recutting group were lost to follow-up at 6 months.

Recutting Group

Mean refraction improved from -1.48 ± 1.25 D before retreatment to -0.07 ± 0.62 D at 1 month (P < .001), -0.48 ± 0.92 D at 3 months (P = .002), and -0.49 ± 0.88 D at 6 months after retreatment (P = 0) (Table 1).

Refractive cylinder changed from -0.70 ± 0.54 D prior to retreatment to -0.55 ± 0.45 D at 1 month (P = .16), -0.64 ± 0.50 D at 3 months (P = .18), and -0.65 ± 0.46 D at 6 months after retreatment (P = .23). These changes were not statistically significant (Table 1).

The percentage of eyes with UCVA of 6/6 increased from 3.8% prior to retreatment to 57.8% at 1 month (P = .003), 62.8% at 3 months (P = .002), and 65.2% at 6 months following retreatment (P < .001). The percentage of eyes with UCVA of 6/12 and better increased from 26.6% prior to retreatment to 87.5% at 1 month (P = .023), 85.9% at 3 months (P = .012), and 84.3% at 6 months (P = .005) following retreatment (Table 2).

Table

Table 1Mean Spherical Equivalent Refraction and Refractive Cylinder After LASIK in Recutting and Flap Lifting Retreatment GroupsTable 2Uncorrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment GroupsTable 3Best Spectacle-corrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 1

Mean Spherical Equivalent Refraction and Refractive Cylinder After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 2

Uncorrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 3

Best Spectacle-corrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment Groups

Table

Table 4Complications of Recutting or Lifting the Flap for Retreatment After LASIK in 318 Eyes

Table 4

Complications of Recutting or Lifting the Flap for Retreatment After LASIK in 318 Eyes

The percentage of eyes with BSCVA of 6/6 changed from 89% before retreatment to 81% at 1 month (P = .23), 82.9% at 3 months (P = .34), and 85.7% at 6 months (P = .42) after retreatment. These changes were not statistically significant.

The percentage of eyes with BSCVA of 6/12 and better changed from 98.8% before retreatment to 95.4% at 1 month (P = .82), 98.3% at 3 months (P = .81), and 99% at 6 months (P = .75) after retreatment. These changes were not statistically significant (Table 3).

Four eyes (1.5%) lost one line of BSCVA, but no eye lost two or more lines of visual acuity. Seven eyes (2.7%) had a free flap complication, two eyes (0.8%) required arcuate transverse keratotomy (ARC-T) for correction of residual astigmatism, and three eyes (1.1%) had flaps with loose lamellar tissue that eventually led to flap removal (Table 4). One eye (0.4%) had significant epithelial ingrowth (grade two) that required removal.10

Flap Lifting Group

Mean refraction improved from -1.05 ± 1.49 D before retreatment to -0.21 ± 0.45 D at 1 month (P < .001), -0.34 ± 0.56 D at 3 months (P < .001), and -0.45 ± 0.39 D at 6 months (P < .001) after retreatment (Table 1).

The refractive cylinder changed from -0.78 ± 0.70 D before retreatment to -0.51 ± 0.46 D at 1 month (P < .001), -0.62 ± 0.43 D at 3 months (P = .005), and -0.70 ± 0.34 D at 6 months (P = 1.000) after retreatment. There was thus no persistent effect (Table 1).

The percentage of eyes with UCVA of 6/6 increased from 3.6% before retreatment to 63.7% at 1 month (P = .002), 68.9% at 3 months (P = .001), and 71.1% at 6 months (P = .004) after retreatment. The percentage of eyes with UCVA of 6/12 and better increased from 32.7% before retreatment to 85.5%. at 1 month (P = .015), 88.9% at 3 months (P = .021), and 89.5% at 6 months (P = .012) after retreatment (Table 2).

The percentage of eyes with BSCVA of 6/6 changed from 83.6% before retreatment to 76.4% at 1 month (P = .84), 77.8% at 3 months (P = .98), and 78.9% at 6 months (P = .87) following retreatment. These changes were not statistically significant. The percentage of eyes with BSCVA of 6/12 and better changed from 100% before retreatment to 98.2% at 1 month (P = .66) following reoperation and 100%' at 3(P = 1.00) and 6 months (P = 1.00) after retreatment. These changes were not statistically significant (Table 3).

Two eyes (3.6%) lost one line of BSCVA and no eye lost two or more lines of visual acuity. Two eyes (3.6%) in the flap lifting group had significant epithelial ingrowth that required removal10 (Table 4).

DISCUSSION

LASIK has become the most popular method for the surgical correction of refractive error. Undercorrection is the most common problem following LASIK.61011 As the amount of treated myopia increases, so too does the amount of regression from the initial myopic correction and the subsequent need for enhancement.12 The regression rate of initial surgical results was reported to be higher in high myopia than moderate myopia.11,13 Maximal regression typically occurs between 2 and 4 weeks postoperatively, and a small rate of regression is generally noted 1 to 3 months later.13 The regression mechanism may be due to postoperative epithelial hyperplasia or an increase in central corneal thickness, causing a steepening of central corneal curvature with a myopic shift.4,14 Undercorrection can be treated either by recutting the cornea or lifting the existing flap.

In our series, the decision whether to recut or lift the flap was considered individually for each eye. We compared the results in patients who had recutting with those whose flaps we lifted in a retrospective manner. Flap lifting was usually performed from 2 to 9 months after the initial procedure and recutting of the cornea from 9 months and later after the initial procedure, although some flaps were lifted much later. In 82.7%' of the eyes the cornea was recut, and in 17.3% of eyes the flap was lifted. In 1996 and 1997, recutting the flap was a more common method of retreatment as it was thought to be faster, with less chance of inducing epithelial ingrowth. As lifting techniques and instrumentation improved, recutting has become less popular, even for retreatments as late as 2 years.

Statistically significant improvement of mean refraction was noted in both groups at all time intervals, with little persistent change in the cylinder. Meanwhile, there was a statistically significant increase in the percentage of eyes with UCVA of 6/6 and with 6/12 or better in both groups.

In the recutting group, there was a small decrease (not statistically significant) in the percentage of eyes with BSCVA of 616 in comparison to before retreatment (from 89% to 85.7% at 6 months following retreatment). This was despite the severe flap complications suffered by a small number of patients. In the flap lifting group, there was also a small decrease (again, not statistically significant) in the percentage of eyes with BSCVA of 6/6 at 6 months following retreatment (from 83.6% to 78.9%). Overall, these results are encouraging and show that, at least in our experience, patients are not at great risk of losing best spectacle-corrected visual acuity as a result of enhancement. In fact, only four eyes (1.5%) lost one line of BSCVA in the recutting group and two eyes (3.6%) lost one line of BSCVA in flap lifting group.

The overall enhancement treatment results for both groups in this study are similar to those reported following single LASIK for high myopia2,6,11 and are similar to those reported in other studies of enhancement.7,8

Epithelial ingrowth, free caps, and astigmatism that required additional arcuate transverse keratotomy (ARC-T) were complications in this study. Overall complications were 3.4% of eyes in the recutting group and 3.6% in the flap lifting group. These results exceed those of another study.5 However, overall, only three eyes (0.9%) had significant epithelial ingrowth, one in the recutting group, and two in the flap lifting group. Flap lifting is reported to be a procedure with higher risk for epithelial ingrowth.12 Excess flap manipulation has been reported to increase the risk of epithelial damage and migration of epithelial cells toward the corneal interface, with consequent trapping of the cells and a high risk of epithelial ingrowth.12,15 However, we had a low incidence of epithelial ingrowth in both groups.

Flap lifting is a widely performed procedure and has been recommended during the first 6 months after LASIK12, although at our institute it has been performed successfully even after 3 years. During the first year after LASIK, the flap edges are generally quite easy to identify and lift. The lifting may take place after marking the flap edge at the slit lamp, using a needle or intraocular lens dialing instrument. The flap may be lifted with minimal epithelial damage using a "flap rhexis" technique, in which the edge of the flap may be lifted and folded backward somewhat, to tear the epithelium, and overcome the peripheral adhesion of the flap, in much the same way as performing a capsulorhexis.

The advantage of recutting is that it does not involve as much manual flap manipulation. It is also particularly appropriate when the primary flap is thin or perforated (lifting such a flap risks further damage), and when there has been significant scarring secondary to inflammation, which may preclude safe lifting of the flap. However, the corneal contour is flatter following LASIK for myopia, increasing the risk of free, perforated, and thin flaps. Furthermore, a second cut can result in loose lamellar wedges of stromal tissue, as the previous interface may respond differently to the surrounding stroma during recutting. Some refractive surgeons advocate a deeper cut, sometimes with minimal temporal displacement of the flap, to avoid the previous interface.15 Cap problems were noted with the recutting procedure in our series. A free cap occurred in seven eyes (2.7%) and three caps were macerated, and required eventual removal.

Whichever technique is used, it is important to exclude corneal ectasia with serial corneal topography and pachymetry. It is also crucial to calculate the amount of posterior tissue (>250 µm) likely to remain after an enhancement procedure.

Residual myopia and myopic astigmatism following LASIK are relatively common. These refractive errors are effectively treated with LASIK enhancement. Both recutting and lifting enhancement procedures were relatively safe and predictable for the correction of residual myopia and myopic astigmatism in our retrospective series, but major flap complications may be more likely to occur with recutting. A randomized, controlled, clinical trial of the two techniques could add further information, but such a trial has not yet been performed.

REFERENCES

1. El-Maghraby A, Salah T, Waring GO, Klyce S, Ibrahim O. Randomized bilateral comparison of excimer laser in situ keratomileusis and photorefractive keratectomy for 2.50 to 8.00 diopters of myopia. Ophthalmology 1999; 106:447-457.

2. Pallikaris IG, Siganos DS. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg 1994;10:498-510.

3. Sutton GS, Kalski RS, Lawless MA, Rogers CM. Excimer retreatment for scarring and regression following PRK for myopia. Brit J Ophthalmol 1995;79:756-759.

4. Lohmann C, Giiell JL. Regression after LASIK for the treatment of myopia: the role of the epithelium. Sem Ophthalmol 1998;13:79-82.

5. Perez-Santonja JJ, Maria JA, Sakla HF, Ruiz-Moreno JM, Alio JL. Re-treatment after laser in situ keratomileusis. Ophthalmology 1999;106:21-27.

6. Perez-Santonja JJ, Bellot J, Claramonte P, Ismail MM, Alio JL. Laser in situ keratomileusis to correct high myopia. J Cataract Refract Surg 1997;23:372-385.

7. Durrie DS, Aziz AA. Lift-flap retreatment after laser in situ keratomileusis. J Refract Surg 1999;15:150-153.

8. Yang B, Chen J, Wang Z. Enhancement ablation for the treatment of undercorrection after excimer laser in situ keratomileusis for correcting myopia. Chin Med J 1998;111: 358-360.

9. Probst LE, Machat JJ. Epithelial ingrowth following LASIK. In: Machat JJ, Slade SG, Probst LE, eds. The Art of LASIK, 2nd Ed. Thorofare, NJ: SLACK, Inc; 1999:427-433.

10. Salah T, Waring GO III, El Maghraby K, Moadel K, Grimm SB. Excimer laser in situ keratomileusis under a corneal flap for myopia of 2 to 20 diopters. Am J Ophthalmol 1996;121:143-155.

11. Guell JL, Müller A. Laser in situ keratomileusis (LASIK) for myopia from -7 to -18 diopters. J Refract Surg 1996;12: 222-228.

12. Probst LE, Machat JJ. Enhancement techniques and results. In: Machat JJ. Slade SG, Probst LE, eds. The Art of LASIK, 2nd ed. Thorofare, NJ: Slack Inc; 1999;225-238.

13. Helmy SA, Salah A, Badawy TT. Sidky AN. Photorefractive keratectomy and laser in situ keratomileusis for myopia between 6.00 and 10.00 diopters. J Refract Surg 1996;12:417-421.

14. Chayet AS, Assil KK, Montes M, Espinosa-Lagana M, Castellanos A, Tsioulias G. Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia. Ophthalmology 1998;105:1194-1199.

15. Pallikaris IG, Papadaki T, Siganos DS. Complex LASIK enhancements. In: Probst LE, ed. Complex Cases with LASIK: Advanced Techniques and Complication Management. Thorofare, NJ: SLACK Inc; 2000:355-365.

Table 1

Mean Spherical Equivalent Refraction and Refractive Cylinder After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 2

Uncorrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 3

Best Spectacle-corrected Visual Acuity After LASIK in Recutting and Flap Lifting Retreatment Groups

Table 4

Complications of Recutting or Lifting the Flap for Retreatment After LASIK in 318 Eyes

10.3928/1081-597X-20010901-02

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