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Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy for the correction of high myopia
articles Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy for the correction of high myopia Jin Kook Kim, MD, Sung Soo Kim, MD, Hyung Keun Lee, MD, In Sik Lee, MD, Gong Je Seong, MD, Eung Kweon Kim, MD, Sueng Han Han, MD Purpose: To compare the visual and refractive outcomes of laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) in the treatment of high myopia. Setting: Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University, and Balgeunsesang Ophthalmology Clinic, Seoul, South Korea. Methods: Four hundred seventy eyes of 240 patients with manifest refraction spherical components greater than –6.00 diopters (D) were assigned to 2 groups: 324 eyes (167 patients) were treated with LASIK and 146 eyes (73 patients), with LASEK. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), remaining refractive error, corneal haze, and complications were followed in both groups for 12 months. Results: At 12 months, the mean spherical equivalent (SE) was within ⫾0.50 D of emmetropia in 205 eyes (63.3%) in the LASIK group and 81 eyes (55.5%) in the LASEK group and within ⫾1.00 D in 261 eyes (80.6%) and 104 eyes (71.2%), respectively. The UCVA was 20/25 or better in 269 LASIK eyes (83.0%) and 111 LASEK eyes (76.0%). There was more than a 1-line loss of BSCVA in 4 LASIK eyes (1.2%) and 21 LASEK eyes (14.3%). The between-group differences in SE, magnitude of cylinder, UCVA, and haze were statistically significant (P⬍.05). Conclusions: Both LASIK and LASEK were safe and effectively treated eyes with high myopia. Laser in situ keratomileusis provided superior results in visual predictability and corneal opacity. J Cataract Refract Surg 2004; 30:1405–1411 2004 ASCRS and ESCRS
L
aser in situ keratomileusis (LASIK) has shown encouraging results in the treatment of high myopia and astigmatism.1–3 Despite the advantages of the procedure, epithelial ingrowth, corneal flap-related complications, and corneal ectasia have been reported.4–6
Accepted for publication December 5, 2003. Reprint requests to Hyung Keun Lee, MD, Department of Ophthalmology, Yong-Dong Severance Hospital, 146-92 Dogok-dong, KangnamGu, Seoul 135-720, South Korea. E-mail: [email protected]. 2004 ASCRS and ESCRS Published by Elsevier Inc.
Laser-assisted subepithelial keratectomy (LASEK) is another approach to photorefractive keratectomy (PRK), which creates an epithelial flap that is replaced after photorefractive ablation. It is hypothesized that the epithelial flap decreases changes in stromal keratocytes and reduces the production of extracellular matrix and collagen.7 This may result in less postoperative haze than with PRK and more favorable visual outcomes. In addition, since no lamellar flap is created, LASEK may retain the biomechanical stability seen with PRK and therefore be an alternative to LASIK, in which corneal thickness may be reduced. 0886-3350/04/$–see front matter doi:10.1016/j.jcrs.2003.12.053
LASIK VERSUS LASEK FOR HIGH MYOPIA
With moderate degrees of myopia, the visual outcomes and incidence of postoperative stromal haze in LASEK patients appear to be superior to those in PRK patients.8–10 Additionally, LASEK has more favorable results than LASIK.11 With surface ablation, the correction of high degrees of myopia produces more corneal haze and regression than the correction of low degrees of myopia.12,13 If the cornea is thick enough, LASIK may be preferred to PRK in eyes with high myopia because of reduced postoperative discomfort, improved immediate acuity, and less corneal haze.14,15 With the suggested advantages of LASEK over PRK, there is a potential for less postoperative discomfort, faster visual rehabilitation, and reduced haze in highly myopic patients. To our knowledge, there has been no comparison of the visual and refractive outcomes of LASIK and LASEK in the treatment of high myopia by a single surgeon. In this study, we retrospectively compared the visual and refractive outcomes, changes in best spectaclecorrected visual acuity (BSCVA), and associated complications in patients who had LASIK or LASEK for high myopia and myopic astigmatism.
Patients and Methods Two hundred forty patients were enrolled in this study between December 2001 and June 2002 for a sample of 470 consecutive eyes. Laser in situ keratomileusis was performed in 324 eyes of 167 patients and LASEK, in 146 eyes of 73 patients. In all patients, myopia was greater than ⫺6.00 diopters (D) (range ⫺6.00 to ⫺12.50 D) and astigmatism was less than 4.50 D. The preoperative ophthalmic examination included slitlamp biomicroscopy, intraocular pressure, fundoscopy, measurement of pupil diameter, Schirmer test, manifest refractions, corneal keratometry, corneal topography, corneal pachymetry, and visual field examination. No patient had a history of refractive procedures, keratoconus, cataract surgery, diabetes, glaucoma, connective tissue disorders, or retinal disease. All refractive surgery was performed by the same surgeon (J.K.K). Both procedures, including the potential advantages, disadvantages, and complications, were fully described to patients who met the criteria. Each patient was then allowed to select the procedure.
Laser In Situ Keratomileusis Laser in situ keratomileusis was performed under topical anesthesia with proparacaine hydrochloride 0.5% (Alcaine威). A rigid eyelid speculum was used. Two radial marks were made with a radial marker dipped in gentian violet at the 1406
12 o’clock and 5 o’clock positions. A Hansatome威 microkeratome (Bausch & Lomb Surgical) was used to create a flap of 160 m. Excess liquid was removed with a Merocel威 sponge (Medtronic Solan). The flap was raised using a spatula and the stromal bed exposed. The Nidek EC-5000 excimer laser was fired on the dried corneal surface with the ablation centered over the entrance pupil. The flap was replaced using a spatula and the peripheral epithelial markings. The epithelial and stromal portions of the flap were then irrigated with a cannula. Postoperatively, ofloxacin 0.3% (Tarivid威) and diclofenac 0.1% were instilled in the treated eye. The lid speculum was removed, and a therapeutic contact lens (Focus威, Bausch & Lomb) was placed on the cornea. Patients were instructed to apply 1 drop of Tarivid and artifical tears (hyaluronic acid 0.1% [Hyalrein威]) every 2 hours. One day postoperatively, the therapeutic contact lens was removed and Tarivid and flurorometholone 0.1% (Fluorometholone) were administrated 4 times daily for 1 week, 2 times daily for 1 month, and once a day for 1 month.
Laser-Assisted Subepithelial Keratectomy A speculum was applied to the patient’s eye, and proparacaine hydrochloride (Alcaine威) was instilled. An alcohol solution cone (J2905, Janach) with an 8.5 mm diameter was placed on the eye. Twenty percent of the alcohol solution was instilled inside the cone, left for about 20 seconds, and then carefully washed off with a balanced salt solution so the epithelium around the flap was not disturbed. The epithelial flap was gently lifted with an epithelial microhoe (J2915A, Janach) and peeled back as a single sheet toward the 12 o’clock position using a spatula (J2910A, Janach). Excimer laser treatment was performed in the usual manner using the same nomogram and laser system as in LASIK. The flap was washed with a balanced salt solution and then repositioned carefully with a spatula. A therapeutic soft contact lens was then placed on the eye. Postoperatively, the eyes were checked daily until the epithelial defect was completely closed. The patients were instructed to apply 1 drop of diclofenac and Tarivid every 2 hours and artificial tears every hour until epithelial healing was complete. After complete reepithelialization had occurred, Tarivid and Fluorometholone were administered 4 times daily for 1 week and 2 times daily for 1 month. Routine postoperative examinations were scheduled at 1 week and then monthly up to 1 year. In the LASEK eyes, daily follow-up examinations were scheduled until epithelial healing was complete; subsequent examinations were as above. The uncorrected visual acuity (UCVA), manifest refraction, tonometry, and slitlamp biomicroscopy were performed at all examinations. Subepithelial corneal haze levels were checked at the slitlamp at 6 and 12 months and graded from 0 to 4 according to the method of Fantes et al.16
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Table 1. Preoperative independent variables. LASIK (n ⫽ 324 Eyes)
Variable
LASEK (n ⫽ 146 Eyes)
P Value
Age* Mean ⫾ SD
28.37 ⫾ 6.71
27.91 ⫾ 4.31
21 ⬃ 39
Range Sex (male/female)
NS*
20 ⬃ 41
55/112
20/53
NS†
Spherical equivalent (D) Mean ⫾ SD
⫺7.91 ⫾ 1.26
⫺8.01 ⫾ 1.85
Range
⫺6.00 ⬃ ⫺11.50
⫺6.00 ⬃ ⫺12.50
NS*
Degree of cylinder Mean ⫾ SD
1.99 ⫾ 0.66
2.13 ⫾ 0.63
Range
0.00 ⬃ 4.50
0.00 ⬃ 4.50
NS*
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; NS ⫽ not significant * Unpaired Student t test † Chi-square test
Data analysis was performed using the Statistical Analysis System (version 6.12, SAS Institute Inc.). The probability value of P⬍.05 was considered statistically significant.
Results The preoperative characteristics of the patients are shown in Table 1. At the preoperative examination, the between-group differences in the independent variables were not statistically significant. The mean postoperative spherical equivalent (SE) changes are shown in Figure 1. From the first month, the remaining SE was higher in the LASEK group than in the LASIK group. At 1 month, the SE appeared slightly hyperopic in both groups but the betweengroup difference was not statistically significant (⫹0.43 D ⫾ 0.78 [SD] in the LASIK group and
Figure 1. (Kim) The mean SE after LASIK and LASEK.
⫹0.51 ⫾ 1.15 D in the LASEK group; P ⫽ .067). From the third month, the between-group difference in the mean SE was statistically significant: ⫺0.29 ⫾ 0.89 D in the LASIK group and ⫺0.61 ⫾ 1.09 D in the LASEK group at 3 months; ⫺0.71 ⫾ 1.14 D and ⫺1.11 ⫾ 1.23, respectively, at 6 months; and ⫺0.77 ⫾ 1.01 D and ⫺1.24 ⫾ 1.31 D, respectively, at 12 months (all P⬍.05). Additionally, in the LASEK eyes, there was a gradual increase in the mean SE at 6 months. In the LASIK eyes, there was little change in the mean SE after 3 months. At 12 months, in the LASIK eyes, the mean SE refraction was within ⫾1.00 D of emmetropia in 261 eyes (80.6%) and within ⫾0.50 D in 205 eyes (63.3%). In the LASEK eyes, it was within ⫾1.00 D of emmetropia in 104 eyes (71.2%) and within ⫾0.50 D in 81 eyes (55.5%) (P ⫽ .00) (Table 2). In LASIK eyes, the mean postoperative astigmatism remained stable from 1 to 12 months. At 1 month, the magnitude of cylinder was within ⫾1.00 D of the intended correction in 303 LASIK eyes (93.5%) and 135 LASEK eyes (92.5%) (P⬎.05). At 12 months, it was within ⫾1.00 D in 295 LASIK eyes (91.1%) and 109 LASEK eyes (74.7%) (P ⫽ .00) (Table 3). The between-group difference in UCVA was statistically significant from 1 to 12 months postoperatively (Table 4). At 12 months, the UCVA was 20/20 or better in 232 LASIK eyes (71.6%) and 88 LASEK eyes (60.3%); 20/25 or better in 269 (83.0%) and 111 (76.0%), respectively; and 20/40 or better in 307
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Table 2. Attempted and achieved SE after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1*
6*
12*
Diopter
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱕ⫾0.50
81.5
71.2
70.1
69.2
63.3
55.5
ⱕ⫾1.00
89.7
82.4
88.6
62.3
80.6
71.2
⬎⫾1.00
10.3
17.8
11.4
37.7
19.4
44.5
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; SE ⫽ spherical equivalent * P⬍.05, chi-square test
Table 3. Magnitude of postoperative refractive cylinder after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1
6*
12*
Diopter
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱕ⫾0.50
77.5
80.3
78.7
58.2
76.5
54.8
ⱕ⫾1.00
93.5
92.5
92.6
76.0
91.1
74.7
⬎⫾1.00
6.5
7.5
7.4
24.0
8.9
25.3
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis * P⬍.05, chi-square test
Table 4. Uncorrected visual acuity after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1*
6*
12*
UCVA
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱖ20/20
82.1
69.9
75.3
63.0
71.6
60.3
ⱖ20/25
90.1
84.3
83.6
77.4
83.0
76.0
ⱖ20/40
98.5
92.5
94.4
89.0
94.8
91.1
⬍20/40
1.5
7.5
5.6
11.0
5.2
8.9
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; UCVA ⫽ uncorrected visual acuity * P⬍.01, chi-square test
Figure 2. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and
Figure 3. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and
LASEK (n ⫽ 146) at 1 month.
LASEK (n ⫽ 146) at 6 months.
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Corneal flap displacements were found on the first postoperative day in 4 LASIK eyes (1.2%). In all 4, corneal flap folds that required repositioning surgery on the same day were found. Epithelial ingrowth, severe diffuse lamellar keratitis, and flap infection were not found in LASIK eyes.
Discussion
Figure 4. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and LASEK (n ⫽ 146) at 12 months.
(94.8%) and 133 (91.1%), respectively (P⬍.01). The BSCVA was better in the LASIK eyes than the LASEK eyes (Figures 2 to 4). There was a 1- or 2-line loss of BSCVA in 4 LASIK eyes (1.2%) and 21 LASEK eyes (14.7%) at 12 months. No LASIK eye lost more than 2 lines of BSCVA. Four LASEK eyes (2.7%) had lost 3 lines at 12 months. Sixteen LASIK eyes (4.9%) and 2 LASEK eyes (1.4%) gained 1 or 2 lines of BSCVA (Figure 4). The main reasons for decreased BSCVA in LASEK eyes were stromal opacity with myopic regression (12.3%), irregular astigmatism (1.4%), and eccentric ablation (0.7%); in LASIK eyes, the reasons were flap-related complications, which were the result of irregular astigmatism, interface haze, and a combination of both. At 1 month, the corneal haze score was less than grade 1 in all eyes. At 12 months, the score was above 2 in 11 LASEK eyes (7.5%). No LASIK eye had detectable haze (Table 5) (P⬍.01).
In our study, LASIK and LASEK corrected high myopic refractive errors successfully up to 1 year postoperatively. However, the LASIK procedure was found to be a more favorable method for correcting high myopia than LASEK. Helmy and coauthors17 report that residual refractive errors were within ⫾1.00 D of emmetropia after LASIK in 34 (85.0%) of 40 eyes with more than ⫺6.00 D of myopia 12 months after surgery using the Summit OmniMed excimer laser. Zaldivar and coauthors2 report that 70 (83.3%) of 84 eyes were within ⫾1.00 D of emmetropia 6 months after surgery using the Nidek EC-5000, which was the laser system used in our study. In LASIK eyes, our outcomes were similar to those in previous reports of LASIK for high myopia. However, when comparing our LASEK results with those in PRK reports, the LASEK method showed superior refractive predictability in correcting high myopia. Previous studies report that 12 months after PRK, the remaining SE was within ⫾1.00 D in 29.0% to 68.0% of eyes.12,17–19 There is controversy about comparing visual and refractive outcomes of LASEK and PRK.10,20,21 However, generally, LASEK eyes have more favorable refractive outcomes than PRK eyes.13,22 The mechanism ex-
Table 5. Incidence and grade of corneal haze after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1* Haze Grade
6*
12*
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
96.0
53.4
63.9
19.9
56.3
15.1
0.5
4.0
32.2
32.4
19.9
38.3
28.1
1
0
14.4
3.1
34.9
2.8
31.5
2
0
0
0.6
19.2
0.6
17.8
3
0
0
0
6.1
0
7.5
4
0
0
0
0
0
0
0
* P⬍.05, chi-square test
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plaining why LASEK produced more favorable refractive results than PRK is not known. The epithelial flap remaining after surgery may help stromal wound healing after excimer laser surgery.8,11,20 Despite the improved surgical results with LASEK, the visual and refractive outcomes in highly myopic eyes were not better after LASEK than after LASIK. The LASIK eyes had a faster recovery and more stable visual acuity than the LASEK eyes. Recovery of useful vision after LASEK took at least 5 days as the corneal epithelium healed, and the vision continued to improve gradually over several months. At 12 months, the between-group difference in UCVA was statistically significant. We think the increased corneal haze and refractive instability in LASEK eyes resulted in the decreased UCVA. Sher et al.23 report a reduction in BSCVA by 2 lines in 15% of eyes after PRK. Recently, Shahinian24 reported a 1-line BSCVA loss in 9 of 55 LASEK-treated eyes (16.3%) at 12 months. In our study, 21 LASEK eyes (14.4%) had a reduction in BSCVA of more than 1 line at 12 months. Regarding BSCVA, our results were similar to those in previous PRK studies. Decreased BSCVA in LASIK eyes is known to be associated with flap-related complications, including a shifted flap, wrinkles, and epithelial ingrowth.25 A loss of 2 or more lines of BSCVA has been reported in between 1.6% and 4.7% of LASIK patients.26,27 In our study, however, only 1.2% of eyes had more than a 1-line loss of BSCVA. We think the decreased incidence of BSCVA loss after LASIK is associated with evolution of the microkeratome and improvement in surgical techniques. Considering the improvement in microkeratome quality, improvement in LASIK results is to be expected. Corneal scars and regression in myopia after excimer laser keratectomy usually develop 1 to 3 months after surgery and persist for several years.23 Thus, it is possible that the corneal haze will diminish and the refractive results and visual acuity improve in the eyes in this study, especially the LASEK eyes. In conclusion, the results of this study indicate that LASIK and LASEK are effective for the correction of high myopia. However, UCVA, BSCVA, predictability of refractive errors, and decreased corneal opacity were better after LASIK than after LASIK up to 1 year postoperatively. A long-term follow-up is needed. 1410
References 1. Trokel SL, Srinivasan R, Braren B. Excimer laser surgery of the cornea. Am J Ophthalmol 1983; 96:710–715 2. Zaldivar R, Davidorf JM, Oscherow S. Laser in situ keratomileusis for myopia from ⫺5.50 to ⫺11.50 diopters with astigmatism. J Refract Surg 1998; 14:19–25 3. Hersh PS, Brint SF, Maloney RK. Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia; a randomized prospective study. Ophthalmology 1998; 105:1512–1523; discussion by JH Talamo, 1522–1523 4. Alio´ JL, Artola A, Claramonte PJ, et al. Complications of photorefractive keratectomy for myopia: two year follow-up of 3000 cases. J Cataract Refract Surg 1998; 24:619–626 5. Schmitt-Bernard C-FM, Lesage C, Arnaud B. Keratectasia induced by laser in situ keratomileusis in keratoconus. J Refract Surg 2000; 16:368–370 6. Seiler T, Holschbach A, Derse M, et al. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153–160 7. Shah S, Sebai Sarhan AR, Doyle SJ, et al. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol 2001; 85:393–396 8. Dastjerdi MH, Soong HK. LASEK (laser subepithelial keratomileusis). Curr Opin Ophthalmol 2002; 13:261– 263 9. Kornilovsy IM. Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg 2001; 17:S222–S223 10. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 2001; 27:565–570 11. Scerrati E. Laser in situ keratomileusis vs laser epithelial keratomileusis (LASIK vs LASEK). J Refract Surg 2001; 17:S219–S221 12. Heitzmann J, Binder PS, Kasser BS, Nordan LT. The correction of high myopia using excimer laser. Arch Ophthalmol 1993; 111:1627–1634 13. Condon PI, Mulhern M, Fulcher T, et al. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol 1997; 81:199–206 14. Pallikaris IG, Papatzanaki ME, Siganos DS, Tsilimbaris MK. A corneal flap technique for laser in situ keratomileusis; human studies. Arch Ophthalmol 1991; 109: 1699–1702 15. 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 16. Fantes FE, Hanna KD, Waring GO III, et al. Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmol 1990; 108:665–675
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17. 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 18. Chan WK, Heng WJ, Tseng P, et al. Photorefractive keratectomy for myopia of 6 to 12 D. J Refract Surg 1995; 11(suppl):S286–S292 19. Tuunanen TH, Tervo TT. Results of photorefractive keratectomy for low, moderate, and high myopia. J Refract Surg 1998; 14:437–446 20. Azar DT, Ang RT, Lee J-B, et al. Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy. Curr Opin Ophthalmol 2001; 12:323–328 21. Litwak S, Zadok D, Garcia-de Quevedo V, et al. Laserassisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia; a prospective study. J Cataract Refract Surg 2002; 28:1330–1333 22. Nakamura K, Kurosaka D, Bissen-Miyajima H, Tsubota K. Intact corneal epithelium is essential for the prevention of stromal haze after laser assisted in situ keratomileusis. Br J Ophthalmol 2001; 85:209–213 23. Sher NA, Hardten DR, Fundingsland B, et al. 193-nm excimer photorefractive keratectomy in high myopia. Ophthalmology 1994; 101:1575–1582
24. Shahinian L Jr. Laser-assisted subepithelial keratectomy for low to high myopia and astigmatism. J Cataract Refract Surg 2002; 28:1334–1342 25. Iskander NG, Peters NT, Anderson Penno E, Gimbel HV. Postoperative complications in laser in situ keratomileusis. Curr Opin Ophthalmol 2000; 11:273–279 26. Gimbel HV, Anderson Penno EE, van Westenbrugge JA, et al. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998; 105:1839–1847; discussion by TE Clinch, 1847– 1848 27. Stulting RD, Carr JD, Thompson KP, et al. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999; 106:13–20 From Balgensesang Ophthalmology Clinic (J.K. Kim, Lee), the Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University (S.S. Kim, H.K. Lee, Seong, E.K. Kim, Han), and BK 21 Project for Medical Science, Yonsei University (E.K. Kim), Seoul, Korea. Supported by grant 02-PJ1-PG1-CH02-003 from the Korea Health 21 R&D Project, Ministry of Health and Welfare, Seoul, South Korea. None of the authors has a commercial or proprietary interest in any material or method mentioned.
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L
aser in situ keratomileusis (LASIK) has shown encouraging results in the treatment of high myopia and astigmatism.1–3 Despite the advantages of the procedure, epithelial ingrowth, corneal flap-related complications, and corneal ectasia have been reported.4–6
Accepted for publication December 5, 2003. Reprint requests to Hyung Keun Lee, MD, Department of Ophthalmology, Yong-Dong Severance Hospital, 146-92 Dogok-dong, KangnamGu, Seoul 135-720, South Korea. E-mail: [email protected]. 2004 ASCRS and ESCRS Published by Elsevier Inc.
Laser-assisted subepithelial keratectomy (LASEK) is another approach to photorefractive keratectomy (PRK), which creates an epithelial flap that is replaced after photorefractive ablation. It is hypothesized that the epithelial flap decreases changes in stromal keratocytes and reduces the production of extracellular matrix and collagen.7 This may result in less postoperative haze than with PRK and more favorable visual outcomes. In addition, since no lamellar flap is created, LASEK may retain the biomechanical stability seen with PRK and therefore be an alternative to LASIK, in which corneal thickness may be reduced. 0886-3350/04/$–see front matter doi:10.1016/j.jcrs.2003.12.053
LASIK VERSUS LASEK FOR HIGH MYOPIA
With moderate degrees of myopia, the visual outcomes and incidence of postoperative stromal haze in LASEK patients appear to be superior to those in PRK patients.8–10 Additionally, LASEK has more favorable results than LASIK.11 With surface ablation, the correction of high degrees of myopia produces more corneal haze and regression than the correction of low degrees of myopia.12,13 If the cornea is thick enough, LASIK may be preferred to PRK in eyes with high myopia because of reduced postoperative discomfort, improved immediate acuity, and less corneal haze.14,15 With the suggested advantages of LASEK over PRK, there is a potential for less postoperative discomfort, faster visual rehabilitation, and reduced haze in highly myopic patients. To our knowledge, there has been no comparison of the visual and refractive outcomes of LASIK and LASEK in the treatment of high myopia by a single surgeon. In this study, we retrospectively compared the visual and refractive outcomes, changes in best spectaclecorrected visual acuity (BSCVA), and associated complications in patients who had LASIK or LASEK for high myopia and myopic astigmatism.
Patients and Methods Two hundred forty patients were enrolled in this study between December 2001 and June 2002 for a sample of 470 consecutive eyes. Laser in situ keratomileusis was performed in 324 eyes of 167 patients and LASEK, in 146 eyes of 73 patients. In all patients, myopia was greater than ⫺6.00 diopters (D) (range ⫺6.00 to ⫺12.50 D) and astigmatism was less than 4.50 D. The preoperative ophthalmic examination included slitlamp biomicroscopy, intraocular pressure, fundoscopy, measurement of pupil diameter, Schirmer test, manifest refractions, corneal keratometry, corneal topography, corneal pachymetry, and visual field examination. No patient had a history of refractive procedures, keratoconus, cataract surgery, diabetes, glaucoma, connective tissue disorders, or retinal disease. All refractive surgery was performed by the same surgeon (J.K.K). Both procedures, including the potential advantages, disadvantages, and complications, were fully described to patients who met the criteria. Each patient was then allowed to select the procedure.
Laser In Situ Keratomileusis Laser in situ keratomileusis was performed under topical anesthesia with proparacaine hydrochloride 0.5% (Alcaine威). A rigid eyelid speculum was used. Two radial marks were made with a radial marker dipped in gentian violet at the 1406
12 o’clock and 5 o’clock positions. A Hansatome威 microkeratome (Bausch & Lomb Surgical) was used to create a flap of 160 m. Excess liquid was removed with a Merocel威 sponge (Medtronic Solan). The flap was raised using a spatula and the stromal bed exposed. The Nidek EC-5000 excimer laser was fired on the dried corneal surface with the ablation centered over the entrance pupil. The flap was replaced using a spatula and the peripheral epithelial markings. The epithelial and stromal portions of the flap were then irrigated with a cannula. Postoperatively, ofloxacin 0.3% (Tarivid威) and diclofenac 0.1% were instilled in the treated eye. The lid speculum was removed, and a therapeutic contact lens (Focus威, Bausch & Lomb) was placed on the cornea. Patients were instructed to apply 1 drop of Tarivid and artifical tears (hyaluronic acid 0.1% [Hyalrein威]) every 2 hours. One day postoperatively, the therapeutic contact lens was removed and Tarivid and flurorometholone 0.1% (Fluorometholone) were administrated 4 times daily for 1 week, 2 times daily for 1 month, and once a day for 1 month.
Laser-Assisted Subepithelial Keratectomy A speculum was applied to the patient’s eye, and proparacaine hydrochloride (Alcaine威) was instilled. An alcohol solution cone (J2905, Janach) with an 8.5 mm diameter was placed on the eye. Twenty percent of the alcohol solution was instilled inside the cone, left for about 20 seconds, and then carefully washed off with a balanced salt solution so the epithelium around the flap was not disturbed. The epithelial flap was gently lifted with an epithelial microhoe (J2915A, Janach) and peeled back as a single sheet toward the 12 o’clock position using a spatula (J2910A, Janach). Excimer laser treatment was performed in the usual manner using the same nomogram and laser system as in LASIK. The flap was washed with a balanced salt solution and then repositioned carefully with a spatula. A therapeutic soft contact lens was then placed on the eye. Postoperatively, the eyes were checked daily until the epithelial defect was completely closed. The patients were instructed to apply 1 drop of diclofenac and Tarivid every 2 hours and artificial tears every hour until epithelial healing was complete. After complete reepithelialization had occurred, Tarivid and Fluorometholone were administered 4 times daily for 1 week and 2 times daily for 1 month. Routine postoperative examinations were scheduled at 1 week and then monthly up to 1 year. In the LASEK eyes, daily follow-up examinations were scheduled until epithelial healing was complete; subsequent examinations were as above. The uncorrected visual acuity (UCVA), manifest refraction, tonometry, and slitlamp biomicroscopy were performed at all examinations. Subepithelial corneal haze levels were checked at the slitlamp at 6 and 12 months and graded from 0 to 4 according to the method of Fantes et al.16
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Table 1. Preoperative independent variables. LASIK (n ⫽ 324 Eyes)
Variable
LASEK (n ⫽ 146 Eyes)
P Value
Age* Mean ⫾ SD
28.37 ⫾ 6.71
27.91 ⫾ 4.31
21 ⬃ 39
Range Sex (male/female)
NS*
20 ⬃ 41
55/112
20/53
NS†
Spherical equivalent (D) Mean ⫾ SD
⫺7.91 ⫾ 1.26
⫺8.01 ⫾ 1.85
Range
⫺6.00 ⬃ ⫺11.50
⫺6.00 ⬃ ⫺12.50
NS*
Degree of cylinder Mean ⫾ SD
1.99 ⫾ 0.66
2.13 ⫾ 0.63
Range
0.00 ⬃ 4.50
0.00 ⬃ 4.50
NS*
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; NS ⫽ not significant * Unpaired Student t test † Chi-square test
Data analysis was performed using the Statistical Analysis System (version 6.12, SAS Institute Inc.). The probability value of P⬍.05 was considered statistically significant.
Results The preoperative characteristics of the patients are shown in Table 1. At the preoperative examination, the between-group differences in the independent variables were not statistically significant. The mean postoperative spherical equivalent (SE) changes are shown in Figure 1. From the first month, the remaining SE was higher in the LASEK group than in the LASIK group. At 1 month, the SE appeared slightly hyperopic in both groups but the betweengroup difference was not statistically significant (⫹0.43 D ⫾ 0.78 [SD] in the LASIK group and
Figure 1. (Kim) The mean SE after LASIK and LASEK.
⫹0.51 ⫾ 1.15 D in the LASEK group; P ⫽ .067). From the third month, the between-group difference in the mean SE was statistically significant: ⫺0.29 ⫾ 0.89 D in the LASIK group and ⫺0.61 ⫾ 1.09 D in the LASEK group at 3 months; ⫺0.71 ⫾ 1.14 D and ⫺1.11 ⫾ 1.23, respectively, at 6 months; and ⫺0.77 ⫾ 1.01 D and ⫺1.24 ⫾ 1.31 D, respectively, at 12 months (all P⬍.05). Additionally, in the LASEK eyes, there was a gradual increase in the mean SE at 6 months. In the LASIK eyes, there was little change in the mean SE after 3 months. At 12 months, in the LASIK eyes, the mean SE refraction was within ⫾1.00 D of emmetropia in 261 eyes (80.6%) and within ⫾0.50 D in 205 eyes (63.3%). In the LASEK eyes, it was within ⫾1.00 D of emmetropia in 104 eyes (71.2%) and within ⫾0.50 D in 81 eyes (55.5%) (P ⫽ .00) (Table 2). In LASIK eyes, the mean postoperative astigmatism remained stable from 1 to 12 months. At 1 month, the magnitude of cylinder was within ⫾1.00 D of the intended correction in 303 LASIK eyes (93.5%) and 135 LASEK eyes (92.5%) (P⬎.05). At 12 months, it was within ⫾1.00 D in 295 LASIK eyes (91.1%) and 109 LASEK eyes (74.7%) (P ⫽ .00) (Table 3). The between-group difference in UCVA was statistically significant from 1 to 12 months postoperatively (Table 4). At 12 months, the UCVA was 20/20 or better in 232 LASIK eyes (71.6%) and 88 LASEK eyes (60.3%); 20/25 or better in 269 (83.0%) and 111 (76.0%), respectively; and 20/40 or better in 307
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Table 2. Attempted and achieved SE after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1*
6*
12*
Diopter
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱕ⫾0.50
81.5
71.2
70.1
69.2
63.3
55.5
ⱕ⫾1.00
89.7
82.4
88.6
62.3
80.6
71.2
⬎⫾1.00
10.3
17.8
11.4
37.7
19.4
44.5
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; SE ⫽ spherical equivalent * P⬍.05, chi-square test
Table 3. Magnitude of postoperative refractive cylinder after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1
6*
12*
Diopter
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱕ⫾0.50
77.5
80.3
78.7
58.2
76.5
54.8
ⱕ⫾1.00
93.5
92.5
92.6
76.0
91.1
74.7
⬎⫾1.00
6.5
7.5
7.4
24.0
8.9
25.3
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis * P⬍.05, chi-square test
Table 4. Uncorrected visual acuity after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1*
6*
12*
UCVA
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
ⱖ20/20
82.1
69.9
75.3
63.0
71.6
60.3
ⱖ20/25
90.1
84.3
83.6
77.4
83.0
76.0
ⱖ20/40
98.5
92.5
94.4
89.0
94.8
91.1
⬍20/40
1.5
7.5
5.6
11.0
5.2
8.9
LASEK ⫽ laser-assisted subepithelial keratectomy; LASIK ⫽ laser in situ keratomileusis; UCVA ⫽ uncorrected visual acuity * P⬍.01, chi-square test
Figure 2. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and
Figure 3. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and
LASEK (n ⫽ 146) at 1 month.
LASEK (n ⫽ 146) at 6 months.
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Corneal flap displacements were found on the first postoperative day in 4 LASIK eyes (1.2%). In all 4, corneal flap folds that required repositioning surgery on the same day were found. Epithelial ingrowth, severe diffuse lamellar keratitis, and flap infection were not found in LASIK eyes.
Discussion
Figure 4. (Kim) Changes in BSCVA after LASIK (n ⫽ 224) and LASEK (n ⫽ 146) at 12 months.
(94.8%) and 133 (91.1%), respectively (P⬍.01). The BSCVA was better in the LASIK eyes than the LASEK eyes (Figures 2 to 4). There was a 1- or 2-line loss of BSCVA in 4 LASIK eyes (1.2%) and 21 LASEK eyes (14.7%) at 12 months. No LASIK eye lost more than 2 lines of BSCVA. Four LASEK eyes (2.7%) had lost 3 lines at 12 months. Sixteen LASIK eyes (4.9%) and 2 LASEK eyes (1.4%) gained 1 or 2 lines of BSCVA (Figure 4). The main reasons for decreased BSCVA in LASEK eyes were stromal opacity with myopic regression (12.3%), irregular astigmatism (1.4%), and eccentric ablation (0.7%); in LASIK eyes, the reasons were flap-related complications, which were the result of irregular astigmatism, interface haze, and a combination of both. At 1 month, the corneal haze score was less than grade 1 in all eyes. At 12 months, the score was above 2 in 11 LASEK eyes (7.5%). No LASIK eye had detectable haze (Table 5) (P⬍.01).
In our study, LASIK and LASEK corrected high myopic refractive errors successfully up to 1 year postoperatively. However, the LASIK procedure was found to be a more favorable method for correcting high myopia than LASEK. Helmy and coauthors17 report that residual refractive errors were within ⫾1.00 D of emmetropia after LASIK in 34 (85.0%) of 40 eyes with more than ⫺6.00 D of myopia 12 months after surgery using the Summit OmniMed excimer laser. Zaldivar and coauthors2 report that 70 (83.3%) of 84 eyes were within ⫾1.00 D of emmetropia 6 months after surgery using the Nidek EC-5000, which was the laser system used in our study. In LASIK eyes, our outcomes were similar to those in previous reports of LASIK for high myopia. However, when comparing our LASEK results with those in PRK reports, the LASEK method showed superior refractive predictability in correcting high myopia. Previous studies report that 12 months after PRK, the remaining SE was within ⫾1.00 D in 29.0% to 68.0% of eyes.12,17–19 There is controversy about comparing visual and refractive outcomes of LASEK and PRK.10,20,21 However, generally, LASEK eyes have more favorable refractive outcomes than PRK eyes.13,22 The mechanism ex-
Table 5. Incidence and grade of corneal haze after LASIK (n ⫽ 224) and LASEK (n ⫽ 146). Month After Surgery (% of Eyes) 1* Haze Grade
6*
12*
LASIK
LASEK
LASIK
LASEK
LASIK
LASEK
96.0
53.4
63.9
19.9
56.3
15.1
0.5
4.0
32.2
32.4
19.9
38.3
28.1
1
0
14.4
3.1
34.9
2.8
31.5
2
0
0
0.6
19.2
0.6
17.8
3
0
0
0
6.1
0
7.5
4
0
0
0
0
0
0
0
* P⬍.05, chi-square test
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plaining why LASEK produced more favorable refractive results than PRK is not known. The epithelial flap remaining after surgery may help stromal wound healing after excimer laser surgery.8,11,20 Despite the improved surgical results with LASEK, the visual and refractive outcomes in highly myopic eyes were not better after LASEK than after LASIK. The LASIK eyes had a faster recovery and more stable visual acuity than the LASEK eyes. Recovery of useful vision after LASEK took at least 5 days as the corneal epithelium healed, and the vision continued to improve gradually over several months. At 12 months, the between-group difference in UCVA was statistically significant. We think the increased corneal haze and refractive instability in LASEK eyes resulted in the decreased UCVA. Sher et al.23 report a reduction in BSCVA by 2 lines in 15% of eyes after PRK. Recently, Shahinian24 reported a 1-line BSCVA loss in 9 of 55 LASEK-treated eyes (16.3%) at 12 months. In our study, 21 LASEK eyes (14.4%) had a reduction in BSCVA of more than 1 line at 12 months. Regarding BSCVA, our results were similar to those in previous PRK studies. Decreased BSCVA in LASIK eyes is known to be associated with flap-related complications, including a shifted flap, wrinkles, and epithelial ingrowth.25 A loss of 2 or more lines of BSCVA has been reported in between 1.6% and 4.7% of LASIK patients.26,27 In our study, however, only 1.2% of eyes had more than a 1-line loss of BSCVA. We think the decreased incidence of BSCVA loss after LASIK is associated with evolution of the microkeratome and improvement in surgical techniques. Considering the improvement in microkeratome quality, improvement in LASIK results is to be expected. Corneal scars and regression in myopia after excimer laser keratectomy usually develop 1 to 3 months after surgery and persist for several years.23 Thus, it is possible that the corneal haze will diminish and the refractive results and visual acuity improve in the eyes in this study, especially the LASEK eyes. In conclusion, the results of this study indicate that LASIK and LASEK are effective for the correction of high myopia. However, UCVA, BSCVA, predictability of refractive errors, and decreased corneal opacity were better after LASIK than after LASIK up to 1 year postoperatively. A long-term follow-up is needed. 1410
References 1. Trokel SL, Srinivasan R, Braren B. Excimer laser surgery of the cornea. Am J Ophthalmol 1983; 96:710–715 2. Zaldivar R, Davidorf JM, Oscherow S. Laser in situ keratomileusis for myopia from ⫺5.50 to ⫺11.50 diopters with astigmatism. J Refract Surg 1998; 14:19–25 3. Hersh PS, Brint SF, Maloney RK. Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia; a randomized prospective study. Ophthalmology 1998; 105:1512–1523; discussion by JH Talamo, 1522–1523 4. Alio´ JL, Artola A, Claramonte PJ, et al. Complications of photorefractive keratectomy for myopia: two year follow-up of 3000 cases. J Cataract Refract Surg 1998; 24:619–626 5. Schmitt-Bernard C-FM, Lesage C, Arnaud B. Keratectasia induced by laser in situ keratomileusis in keratoconus. J Refract Surg 2000; 16:368–370 6. Seiler T, Holschbach A, Derse M, et al. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153–160 7. Shah S, Sebai Sarhan AR, Doyle SJ, et al. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol 2001; 85:393–396 8. Dastjerdi MH, Soong HK. LASEK (laser subepithelial keratomileusis). Curr Opin Ophthalmol 2002; 13:261– 263 9. Kornilovsy IM. Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg 2001; 17:S222–S223 10. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 2001; 27:565–570 11. Scerrati E. Laser in situ keratomileusis vs laser epithelial keratomileusis (LASIK vs LASEK). J Refract Surg 2001; 17:S219–S221 12. Heitzmann J, Binder PS, Kasser BS, Nordan LT. The correction of high myopia using excimer laser. Arch Ophthalmol 1993; 111:1627–1634 13. Condon PI, Mulhern M, Fulcher T, et al. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol 1997; 81:199–206 14. Pallikaris IG, Papatzanaki ME, Siganos DS, Tsilimbaris MK. A corneal flap technique for laser in situ keratomileusis; human studies. Arch Ophthalmol 1991; 109: 1699–1702 15. 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 16. Fantes FE, Hanna KD, Waring GO III, et al. Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmol 1990; 108:665–675
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17. 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 18. Chan WK, Heng WJ, Tseng P, et al. Photorefractive keratectomy for myopia of 6 to 12 D. J Refract Surg 1995; 11(suppl):S286–S292 19. Tuunanen TH, Tervo TT. Results of photorefractive keratectomy for low, moderate, and high myopia. J Refract Surg 1998; 14:437–446 20. Azar DT, Ang RT, Lee J-B, et al. Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy. Curr Opin Ophthalmol 2001; 12:323–328 21. Litwak S, Zadok D, Garcia-de Quevedo V, et al. Laserassisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia; a prospective study. J Cataract Refract Surg 2002; 28:1330–1333 22. Nakamura K, Kurosaka D, Bissen-Miyajima H, Tsubota K. Intact corneal epithelium is essential for the prevention of stromal haze after laser assisted in situ keratomileusis. Br J Ophthalmol 2001; 85:209–213 23. Sher NA, Hardten DR, Fundingsland B, et al. 193-nm excimer photorefractive keratectomy in high myopia. Ophthalmology 1994; 101:1575–1582
24. Shahinian L Jr. Laser-assisted subepithelial keratectomy for low to high myopia and astigmatism. J Cataract Refract Surg 2002; 28:1334–1342 25. Iskander NG, Peters NT, Anderson Penno E, Gimbel HV. Postoperative complications in laser in situ keratomileusis. Curr Opin Ophthalmol 2000; 11:273–279 26. Gimbel HV, Anderson Penno EE, van Westenbrugge JA, et al. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998; 105:1839–1847; discussion by TE Clinch, 1847– 1848 27. Stulting RD, Carr JD, Thompson KP, et al. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999; 106:13–20 From Balgensesang Ophthalmology Clinic (J.K. Kim, Lee), the Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University (S.S. Kim, H.K. Lee, Seong, E.K. Kim, Han), and BK 21 Project for Medical Science, Yonsei University (E.K. Kim), Seoul, Korea. Supported by grant 02-PJ1-PG1-CH02-003 from the Korea Health 21 R&D Project, Ministry of Health and Welfare, Seoul, South Korea. None of the authors has a commercial or proprietary interest in any material or method mentioned.
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