- Email: [email protected]
Laser-assisted subepithelial keratectomy for myopia: two-year follow-up1
Laser-assisted subepithelial keratectomy for myopia: Two-year follow-up Rudolf Autrata, MD, PhD, Jaroslav Rehurek, MD, PhD Purpose: To assess and compare the clinical results (efficacy, safety, stability, and postoperative pain or discomfort) of laser-assisted subepithelial keratectomy (LASEK) and conventional photorefractive keratectomy (PRK) for the correction of low to moderate myopia. Setting: Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. Methods: A prospective comparative study was performed in 184 eyes of 92 patients who had surface excimer ablation for the correction of myopia. The preoperative mean spherical equivalent (MSE) was ⫺4.65 diopters (D) ⫾ 3.14 (SD) (range ⫺1.75 to ⫺7.50 D). In each patient, LASEK was performed in 1 eye and PRK in the fellow eye by the same surgeon. The first eye treated and the surgical method used in the first eye were randomized. Both procedures were performed with the Nidek EC-5000 excimer laser using the same parameters and nomogram. The postoperative pain level, visual recovery, complications (haze), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and refractive outcome were evaluated and compared. All eyes completed a 24-month follow-up. Results: The postoperative MSE was ⫺0.18 ⫾ 0.53 D in the PRK eyes and ⫺0.33 ⫾ 0.46 D in the LASEK eyes. At 1 week, the mean UCVA was 0.64 ⫾ 0.21 and 0.87 ⫾ 0.23, respectively. No LASEK eye lost a line of BSCVA. There were no statistically significant differences between PRK and LASEK eyes in the safety and efficacy indices at 2 years. The mean pain level was significantly lower on days 1 to 3 in the LASEK eyes (P ⬍ .05). The mean corneal haze level was lower in the LASEK eyes (0.21) than in the PRK eyes (0.43) (P ⬍ .05). Seventy-nine patients preferred LASEK to PRK. Conclusions: Laser-assisted subepithelial keratectomy provided significantly quicker visual recovery, eliminated post-PRK pain, and reduced the haze level in eyes with low to moderate myopia compared with conventional PRK. It provided good visual and refractive outcomes. There were no serious complications. J Cataract Refract Surg 2003; 29:661– 668 © 2003 ASCRS and ESCRS
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xcimer laser refractive surgery has become popular during the past 10 years. Photorefractive keratectomy (PRK) has proved to be safe and effective for treating low to moderate myopia.1–9 However, the relatively long visual recovery period, postoperative pain, myopic regression, and complications, especially Accepted for publication September 24, 2002. Reprint requests to Rudolf Autrata, MD, PhD, Department of Ophthalmology, Masaryk University Hospital, Cernopolni 9, Brno 61300, Czech Republic. E-mail: [email protected]. © 2003 ASCRS and ESCRS Published by Elsevier Science Inc.
stromal haze,10 –12 have led many surgeons to perform laser in situ keratomileusis (LASIK). The increase in the number of LASIK procedures has caused a rise in the number of flap- and interfacerelated complications unique to LASIK; ie, wrinkled flaps,13 late flap dislocations,14 dry-eye symptoms,15 diffuse lamellar keratitis,16 epithelial ingrowth within the flap interface,17 difficulty predicting flap thickness and ablation depth,18 and posterior ectasia.19 Laser-assisted subepithelial keratectomy (LASEK) may combine the advantages and eliminate the disad0886-3350/03/$–see front matter doi:10.1016/S0886-3350(02)01897-7
LASEK VERSUS PRK FOR MYOPIA
vantages of PRK and LASIK. This study compared LASEK and PRK results in visual acuity, refractive stability, safety, and complications in a randomized clinical study of LASEK in 1 eye and PRK in the contralateral eye.
Patients and Methods Ninety-two patients (184 eyes) with myopia were enrolled in the study between April 1999 and February 2000. In each patient, PRK was performed in 1 eye and LASEK in the fellow eye by the same surgeon (A.R.). The first eye treated and the surgical method in the first eye were randomized. All patients received a full explanation of both procedures and provided informed consent before surgery. However, they also provided signed approval to not know which technique was performed in each eye. The interval between the 2 procedures was 2 to 6 weeks in all patients. The mean patient age was 27.4 years (range 18 to 39 years). Preoperatively, the mean spherical equivalent (MSE) in the 184 eyes was ⫺4.65 diopters (D) (range ⫺1.75 to ⫺7.50 D). The mean best spectacle-corrected visual acuity (BSCVA) was 20/40 or better in all eyes: 20/20 in 161 eyes (87.5%), 20/30 in 18 eyes (9.8%), and 20/40 in 5 eyes (2.7%). All patients had stable refractions for at least 12 months. The preoperative ophthalmic examination in all patients included uncorrected visual acuity (UCVA), BSCVA, slitlamp microscopy, fundus examination, cycloplegic and manifest refractions, corneal keratometry, corneal topography, Goldmann tonometry, pachymetry, and the Schirmer test. All eyes had cycloplegic refractions within ⫾0.5 D of the manifest refraction. The pupil diameter was measured under scotopic illumination, and the ablation zone diameter used was larger than the scotopic pupil diameter. Patients who wore soft contact lenses were asked to discontinue use 14 days before the examination. Patients with diabetes mellitus, connective tissue disease, corneal disease, cataract, glaucoma, and retinal disease were excluded. Eight of 100 LASEK eyes (8%) had to be converted to PRK because the epithelial flap disintegrated. However, these “converted” eyes were excluded from further evaluation for the comparative study. All procedures were performed using the Nidek EC-5000 excimer laser with a 6.5 mm ablation optical zone and a 7.5 mm transition zone. Multizone ablations were performed in eyes with myopia greater than ⫺4.0 D. The same nomogram (Nidek version 2.25 dH for PRK and LASEK) was used. Photorefractive keratectomy was performed under topical anesthesia with oxybuprocaine chloride 0.5% (Novesin威). Deepithelialization was performed with a blunt spatula after the epithelium was marked with a 7.5 mm trephine centered at the point at which the visual axis intersected the anterior 662
corneal surface. The corneal surface was cooled by continuous irrigation of chilled (8°C) fortified balanced salt solution (BSS Plus威) for 30 seconds just before the ablation. The laser ablation was performed and immediately afterward, the surface was again cooled by irrigation with chilled BSS Plus for 30 seconds. At the end of the procedure, a drop of tobramycin 0.3% (Tobrex威) and a drop of diclofenac 0.1% (Naclof威) were administered and a therapeutic contact lens (Acuvue威, Vistakon) was applied to the eye. Patients were seen daily until the epithelial defect completely closed and were instructed to apply 1 drop of both Tobrex and Naclof 5 times a day and artificial tears (Tears Naturale Free威) every 2 hours until the epithelium healed. After complete reepithelialization occurred, fluorometholone 0.1% eyedrops (Flucon威) were administered 5 times daily for the first month, 4 times daily for the second month, 3 times daily for the third month, twice daily for the fourth month, and once a day for the fifth and sixth months. In LASEK, the cornea was anesthetized with 5 drops of Novesin. The eye was prepared with povidone–iodine (Betadine威), and a plastic drape and lid speculum were applied. An 8.0 mm LASEK corneal trephine (Janach J2900) was used to create an epithelial incision. The corneal trephine is designed to create a 270-degree epithelial incision with a blunt section at 12 o’clock for the formation of a hinge. The blade was placed centrally on the visual axis; slight rotation of the blade was used to facilitate creation of the epithelial incision. An alcohol solution cone (Janach J2905) with an 8.5 mm diameter was placed on the eye. Twenty percent of the ethyl alcohol solution was instilled inside the alcohol solution cone and left for 25 to 30 seconds. The alcohol solution was then absorbed with a small surgical sponge. The area was thoroughly rinsed for 30 seconds with balanced salt solution (BSS威) and dried with a surgical sponge. An epithelial microhoe (Janach J2915A) was used to create the flap by lifting the edges of the epithelial incision. The epithelial flap was gently detached and folded at the 12 o’clock position. After laser ablation, the cornea was flooded with chilled (8°C) BSS for 20 to 30 seconds and the epithelial flap was carefully repositioned using a blunt spatula (Janach J2920A). The same type of therapeutic soft contact lens as in the PRK procedure was placed on the eye and the same topical eyedrops were instilled. The soft contact lens was removed 2 to 3 days after the procedure. The regimen of fluorometholone eyedrops used in the PRK eyes was used in most LASEK eyes. However, the regimen was individualized in 18 eyes based on a stable refraction, excellent visual acuity, and clear cornea and stopped at the end of the fifth month. The patients were examined on days 1 to 4 until the epithelium healed. The time required for complete epithelialization was recorded. The UCVA, BSCVA, and refraction were measured at 1 week and 1, 3, 6, 12, and 24 months. Subepithelial corneal haze levels were detected by slitlamp
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examination and graded from 0 to 4 according to Epstein and coauthors20 at 1, 3, 6, 12, and 24 months: 0, completely clear; 1, faint haze detectable only with broad tangential illumination; 2, discrete haze visible with difficulty by focal illumination and refraction possible; 3, moderately dense opacity partly obscuring iris detail; 4, severely dense opacity completely obscuring details of intraocular structures. At 1 week, patients were asked to complete a questionnaire about the pain they experienced using a 4-point scale: 0, no pain or discomfort; 1, mild burning, stinging, or mild pain; 2, moderate and more prolonged burning, stinging, or aching; 3, severe constant or sharp pain or aching that requires more analgesics to relieve. After 6 months, all patients were asked which procedure they preferred. The refractive surgical data for analysis and comparison adhered to published guidelines.21 Data from each patient were entered into Microsoft Excel (Office 97) to create a database and perform a statistical analysis of the 2 groups. An unpaired t test was used to compare the MSE refractions. The Mann-Whitney test was used to compare postoperative pain scores and corneal haze scores in the PRK and LASEK eyes. The Fisher exact test was used for analysis of categorized data. A P value less than 0.05 was considered significant.
Figure 1. (Autrata) Stability of refraction: The MSE refraction preoperatively and postoperatively.
Efficacy At 1 week, the mean UCVA was 0.64 ⫾ 0.21 in the PRK eyes and 0.87 ⫾ 0.23 in the LASEK eyes. The difference was statistically significant (P ⫽ .034). At 1 month and 1 and 2 years, the between-group differences in UCVA were not statistically significant (Table 2). The UCVA results at 24 months are shown in Table 3 and Figure 2. There were no statistically significant between-group differences in the mean UCVA or the efficacy index. The efficacy index (Table 4) was better in LASEK eyes (0.978) than in PRK eyes (0.967), but the difference was not significant (P ⫽ .78)
Results Refraction Preoperatively, the MSE manifest refraction was ⫺4.78 D ⫾ 2.93 (SD) (range ⫺2.0 to ⫺7.0 D) in the PRK eyes and ⫺4.90 ⫾ 3.01 D (range ⫺1.75 to ⫺7.50 D) in the LASEK eyes. The difference was not statistically significant (P ⫽ .69). At 2 years, the MSE manifest refraction was ⫺0.18 ⫾ 0.53 D (range ⫹0.50 to ⫺1.50 D) and ⫺0.23 ⫾ 0.46 D (range ⫹0.75 to ⫺1.25 D), respectively; the difference was not statistically significant (P ⫽ .83). The MSE manifest refraction preoperatively and postoperatively is shown in Table 1 and Figure 1.
Safety At 2 years, the mean BSCVA was 0.95 ⫾ 0.16 in the PRK eyes and 0.98 ⫾ 0.14 in the LASEK eyes. The safety index was 1.032 and 1.043, respectively (Table 5). This difference was not statistically significant. Four PRK eyes and no LASEK eye lost 1 Snellen line of BSCVA. The change in Snellen lines of BSCVA at 24 months is shown in Table 6 and Figure 3. Sixty-eight
Table 1. The MSE refraction preoperatively and postoperatively. MSE Refraction Postoperative (Mo) Group (n)
Preop
1
3
6
12
24
PRK (92)
⫺4.78 ⫾ 2.93
0.95 ⫾ 1.15
0.51 ⫾ 0.84
0.26 ⫾ 0.63
⫺0.23 ⫾ 0.59
⫺0.18 ⫾ 0.53
LASEK (92)
⫺4.90 ⫾ 3.01
0.81 ⫾ 0.95
0.39 ⫾ 0.71
0.18 ⫾ 0.48
⫺0.21 ⫾ 0.43
⫺0.23 ⫾ 0.46
⬎.05
⬎.05
⬎.05
⬎.05
⬎.05
⬎.05
P value
MSE ⫽ mean spherical equivalent; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
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Table 2. The mean UCVA postoperatively.
Table 4. Efficacy index (mean postop UCVA/mean preop BSCVA) at 24 months.
Mean UCVA Postoperatively Group (n)
1 Week
1 Month
1 Year
PRK (92)
0.64 ⫾ 0.21
0.78 ⫾ 0.22
0.88 ⫾ 0.17
LASEK (92)
0.87 ⫾ 0.23
0.89 ⫾ 0.18
0.91 ⫾ 0.20
⬍.05
⬎.05
⬎.05
P value
UCVA ⫽ uncorrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 3. Efficacy: UCVA at 24 months.
Mean Postop UCVA
Mean Preop BSCVA
Efficacy Index
PRK (92)
0.89 ⫾ 0.18
0.92 ⫾ 0.13
0.967
LASEK (92)
0.92 ⫾ 0.17
0.94 ⫾ 0.19
0.978
⬎.05
⬎.05
⬎.05
Group (n)
P value
UCVA ⫽ uncorrected visual acuity; BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 5. Safety index (mean postop BSCVA/mean preop BSCVA) at 24 months.
UCVA, n (%) Group (n)
20/20
20/25–20/40
>20/40
PRK (92)
62 (67)
20 (22)
10 (11)
LASEK (92)
67 (73)
17 (18)
8 (9)
⬎.05
⬎.05
P value
⬎.05
UCVA ⫽ uncorrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
PRK eyes (73.9%) had no change in BSCVA, 15 (16.3%) gained 1 line, and 5 (5.4%) gained 2 lines. Seventy-one LASEK eyes (77.1%) had no change in BSCVA, 18 (19.6%) gained 1 line, and 3 (3.3%) gained 2 lines. Predictability At 2 years, 62% of the LASEK eyes and 57% of the PRK eyes were within ⫾0.5 D of the desired refraction and 92% and 91%, respectively, were within ⫾1.0 D (Figure 4). There were no significant between-group
Mean Postop BSCVA
Mean Preop BSCVA
Safety Index
PRK (92)
0.95 ⫾ 0.16
0.92 ⫾ 0.13
1.032
LASEK (92)
0.98 ⫾ 0.14
0.94 ⫾ 0.19
1.043
⬎.05
⬎.05
⬎.05
Group (n)
P value
BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 6. Safety: Change in Snellen lines of BSCVA at 24 months. Snellen Lines of BSCVA, n (%) 2 Lost
1 Lost
No Change
1 Gained
2 Gained
PRK (92)
0
4 (4.5)
68 (73.9)
15 (16.3)
5 (5.4)
LASEK (92)
0
0
71 (77.1)
18 (19.6)
3 (3.3)
Group (n)
P ⬎.05 BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
differences. Three PRK eyes (3.2%) and 2 LASEK eyes (2.1%) were overcorrected 1.0 to 2.0 D. No eye in either group was overcorrected more than 2.0 D.
Figure 2. (Autrata) Efficacy: the UCVA at 2 years. 664
Haze At 1 month, the mean corneal haze score was 0.85 ⫾ 0.79 in PRK eyes and 0.52 ⫾ 0.64 in LASEK eyes, a statistically significant difference (P ⫽ .023). The difference was also significant at 3 months (P ⫽ .035) and 6 months (P ⫽ .028). The mean haze intensity then decreased, but the between-group difference was significant at 12 and 24 months (Figure 5 and Table 7). No
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Figure 3. (Autrata) Change in Snellen lines of BSCVA.
Postoperative Pain and Discomfort Based on the subjective questionnaire, the mean postoperative pain and discomfort scores were 1.82 ⫾ 1.34 in the PRK eyes and 1.06 ⫾ 0.90 in the LASEK eyes at 1 day; the difference was statistically significant (P ⫽ .019). The between-group differences at 2 and 3 days as well as overall were significant (Figure 6 and Table 8). The epithelial defect was completely healed by day 3 in the LASEK eyes and by day 5 in the PRK eyes. The mean epithelial healing time was 2.76 ⫾ 0.47 days (range 2 to 3 days) and 3.95 ⫾ 0.71 days (range 3 to 5 days), respectively. The difference was statistically significant (P ⫽ .033). Seventy-nine patients (86%) preferred the LASEK procedure because of less pain and discomfort, faster visual rehabilitation, and better visual acuity. There were no postoperative complications such as infection, recurrent erosion syndrome, or dry-eye problems. To date, no patient has required retreatment.
Discussion Figure 4. (Autrata) The refractive outcome (SE ⫽ spherical equivalent) at 24 months.
Figure 5. (Autrata) The mean corneal haze level postoperatively.
correlation between the haze scores and the refractive regression in PRK and LASEK eyes was found. The mean haze level differences between PRK and LASEK eyes were statistically significant. No significant between-group differences in the MSE refraction were found.
Over the past 2 years, investigators have reported advantages and encouraging results with LASEK. Lee et al.22 compared LASEK and PRK for the correction of myopia up to ⫺6.5 D in a prospective study of 27 patients with a 3-month follow-up. The results proved the efficacy and safety of LASEK. The incidence of postoperative pain and corneal haze was reduced in the LASEK eyes. Claringbold23 reported 12-month results in 222 consecutive eyes that had LASEK for myopia up to ⫺11.25 D. The study demonstrates that LASEK may be an excellent, effective, and safe alternative to LASIK for the surgical correction of myopia. Further prospective studies and a long-term evaluation should be done to confirm the role of LASEK in excimer laser refractive surgery. Our 2-year results of LASEK correction for myopia up to ⫺7.50 D indicate that the procedure may eliminate or reduce the complications of PRK and LASIK. Use of the epithelial flap decreased the time to epithelial healing. The reduced pain in LASEK eyes is probably because the epithelial flap acts as a biological therapeutic lens that protects the ablated stroma. The LASEK eyes achieved visual recovery sooner than the PRK eyes. At 1 week, the UCVA was better in the LASEK eyes than in
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Table 7. Mean corneal haze level. Postoperative (Mo) Mean Corneal Haze Group (n)
1
3
6
12
24
PRK (92)
0.85 ⫾ 0.79
1.14 ⫾ 0.63
1.06 ⫾ 0.52
0.54 ⫾ 0.31
0.43 ⫾ 0.29
LASEK (92)
0.52 ⫾ 0.64
0.73 ⫾ 0.51
0.61 ⫾ 0.40
0.35 ⫾ 0.28
0.21 ⫾ 0.24
.023
.035
.028
.038
.042
P value
n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
prevalent in LASEK eyes than in PRK eyes during the entire follow-up. The specific underlying cellular events of less corneal stromal fibrosis or scarring after LASEK remain unclear. Various cytokines including keratinocyte growth factor and transforming growth factor  (TGF-) are known to regulate the corneal stromal wound-healing process after excimer laser keratectomy.24 –26 Among these cytokines, TGF- is proposed to be key in inducing corneal stromal fibrosis after excimer laser keratectomy. It has been shown that the increased expression of TGF- and TGF- receptors in keratocytes plays a role in the activation and proliferation of keratocytes and the production of extracellular matrix components, leading to corneal fibrosis after excimer laser keratectomy.24 It has been reported that the expression of TGF-1 in the keratocytes is lower after LASIK than after PRK. This indicates that the corneal stromal fibrosis regulated by TGF-1 is less after LASIK than after PRK.27 There may be a similar effect in the LASEK procedure, leading to decreased corneal stromal fibrosis. The epithelial flap repositioning may decrease the initial loss of anterior stromal keratocytes and late subepithelial fibroblast hyperplasia, which is similar to the effect of applying a human amniotic membrane after PRK.28 Laser-assisted subepithelial keratectomy can be used instead of LASIK in the case of a thin cornea and a large
Figure 6. (Autrata) The mean level of postoperative pain and discomfort.
the PRK eyes. The remaining epithelial flap acts as a smooth refractive surface, and this allows better initial visual acuity. In contrast to a previous report,22 the epithelial healing time was significantly lower with LASEK than with PRK. We believe that multizone ablation (for myopia greater than ⫺4.0 D), instillation of chilled BSS immediately after ablation, and, especially, epithelial flap repositioning may explain the elimination of early stromal haze in the LASEK eyes. The lack of late-onset corneal haze, even in eyes with moderate myopia up to ⫺7.5 D, is a promising aspect of LASEK. Corneal haze was less Table 8. Mean level of postoperative pain and discomfort.
Mean Postoperative Pain Group (n)
1 Day
2 Days
3 Days
Overall Level
PRK (92)
1.82 ⫾ 1.34
1.33 ⫾ 0.82
0.81 ⫾ 0.54
1.26 ⫾ 0.91
LASEK (92)
1.06 ⫾ 0.90
0.56 ⫾ 0.37
0.30 ⫾ 0.43
0.61 ⫾ 0.53
.019
.024
.0263
.0387
P value
n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy Pain scale: 0 ⫽ no pain; 4 ⫽ severe pain
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correction, a small palpebral fissure or deep-set eye, or a neovascularized cornea due to incorrect contact lens use. In addition, LASEK should be considered the procedure of choice to reduce the risk of late flap trauma or dislocation. Laser-assisted subepithelial keratectomy may be a better method than LASIK for customized ablations. It may provide an improved flap–stromal interface that enhances the visual benefit provided by wavefront technology. The LASEK procedure requires more surgical training, but if creation of the epithelial flap is unsuccessful, the surgeon can easily convert to PRK. Further investigation is needed to evaluate LASEK for the correction of higher levels of myopia. We performed a study of LASEK in a group 58 patients with myopia of ⫺6.0 to ⫺10.0 D. The initial results of a 1-year follow-up are promising. In conclusion, our study demonstrated that LASEK can be an effective and safe method for the correction of low to moderate myopia up to ⫺7.5 D. It provided significantly quicker visual recovery and caused less haze than conventional PRK, and it eliminated post-PRK pain.
9.
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13. 14.
15.
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17.
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ing growth factor  superfamily and their receptors in the corneal stromal wound healing process after excimer laser keratectomy [letter]. Br J Ophthalmol 1998; 82:462– 463 25. Malley DS, Steinert RF, Puliafito CA, Dobi ET. Immunofluorescence study of corneal wound healing after excimer laser anterior keratectomy in the monkey eye. Arch Ophthalmol 1990; 108:1316 –1322 26. Wilson SE, Walker JW, Chwang EL, He Y-G. Hepatocyte growth factor, keratinocyte growth factor, their receptors, fibroblast growth factor receptor-2, and the cells of the cornea. Invest Ophthalmol Vis Sci 1993; 34:2544 –2561 27. Kaji Y, Soya K, Amano S, et al. Relation between corneal haze and transforming growth factor-1 after photore-
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fractive keratectomy and laser in situ keratomileusis. J Cataract Refract Surg 2001; 27:1840 –1846 28. Choi YS, Kim JY, Wee WR, Lee JH. Effect of the application of human amniotic membrane on rabbit corneal wound healing after excimer laser photorefractive keratectomy. Cornea 1998; 17:389 –395 From the Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. Presented in part at the XIX Congress of the European Society of Cataract & Refractive Surgeons, Amsterdam, The Netherlands, September 2001. Supported by the University Hospital Brno, Brno, Czech Republic. Neither author has a financial or proprietary interest in any product mentioned.
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xcimer laser refractive surgery has become popular during the past 10 years. Photorefractive keratectomy (PRK) has proved to be safe and effective for treating low to moderate myopia.1–9 However, the relatively long visual recovery period, postoperative pain, myopic regression, and complications, especially Accepted for publication September 24, 2002. Reprint requests to Rudolf Autrata, MD, PhD, Department of Ophthalmology, Masaryk University Hospital, Cernopolni 9, Brno 61300, Czech Republic. E-mail: [email protected]. © 2003 ASCRS and ESCRS Published by Elsevier Science Inc.
stromal haze,10 –12 have led many surgeons to perform laser in situ keratomileusis (LASIK). The increase in the number of LASIK procedures has caused a rise in the number of flap- and interfacerelated complications unique to LASIK; ie, wrinkled flaps,13 late flap dislocations,14 dry-eye symptoms,15 diffuse lamellar keratitis,16 epithelial ingrowth within the flap interface,17 difficulty predicting flap thickness and ablation depth,18 and posterior ectasia.19 Laser-assisted subepithelial keratectomy (LASEK) may combine the advantages and eliminate the disad0886-3350/03/$–see front matter doi:10.1016/S0886-3350(02)01897-7
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vantages of PRK and LASIK. This study compared LASEK and PRK results in visual acuity, refractive stability, safety, and complications in a randomized clinical study of LASEK in 1 eye and PRK in the contralateral eye.
Patients and Methods Ninety-two patients (184 eyes) with myopia were enrolled in the study between April 1999 and February 2000. In each patient, PRK was performed in 1 eye and LASEK in the fellow eye by the same surgeon (A.R.). The first eye treated and the surgical method in the first eye were randomized. All patients received a full explanation of both procedures and provided informed consent before surgery. However, they also provided signed approval to not know which technique was performed in each eye. The interval between the 2 procedures was 2 to 6 weeks in all patients. The mean patient age was 27.4 years (range 18 to 39 years). Preoperatively, the mean spherical equivalent (MSE) in the 184 eyes was ⫺4.65 diopters (D) (range ⫺1.75 to ⫺7.50 D). The mean best spectacle-corrected visual acuity (BSCVA) was 20/40 or better in all eyes: 20/20 in 161 eyes (87.5%), 20/30 in 18 eyes (9.8%), and 20/40 in 5 eyes (2.7%). All patients had stable refractions for at least 12 months. The preoperative ophthalmic examination in all patients included uncorrected visual acuity (UCVA), BSCVA, slitlamp microscopy, fundus examination, cycloplegic and manifest refractions, corneal keratometry, corneal topography, Goldmann tonometry, pachymetry, and the Schirmer test. All eyes had cycloplegic refractions within ⫾0.5 D of the manifest refraction. The pupil diameter was measured under scotopic illumination, and the ablation zone diameter used was larger than the scotopic pupil diameter. Patients who wore soft contact lenses were asked to discontinue use 14 days before the examination. Patients with diabetes mellitus, connective tissue disease, corneal disease, cataract, glaucoma, and retinal disease were excluded. Eight of 100 LASEK eyes (8%) had to be converted to PRK because the epithelial flap disintegrated. However, these “converted” eyes were excluded from further evaluation for the comparative study. All procedures were performed using the Nidek EC-5000 excimer laser with a 6.5 mm ablation optical zone and a 7.5 mm transition zone. Multizone ablations were performed in eyes with myopia greater than ⫺4.0 D. The same nomogram (Nidek version 2.25 dH for PRK and LASEK) was used. Photorefractive keratectomy was performed under topical anesthesia with oxybuprocaine chloride 0.5% (Novesin威). Deepithelialization was performed with a blunt spatula after the epithelium was marked with a 7.5 mm trephine centered at the point at which the visual axis intersected the anterior 662
corneal surface. The corneal surface was cooled by continuous irrigation of chilled (8°C) fortified balanced salt solution (BSS Plus威) for 30 seconds just before the ablation. The laser ablation was performed and immediately afterward, the surface was again cooled by irrigation with chilled BSS Plus for 30 seconds. At the end of the procedure, a drop of tobramycin 0.3% (Tobrex威) and a drop of diclofenac 0.1% (Naclof威) were administered and a therapeutic contact lens (Acuvue威, Vistakon) was applied to the eye. Patients were seen daily until the epithelial defect completely closed and were instructed to apply 1 drop of both Tobrex and Naclof 5 times a day and artificial tears (Tears Naturale Free威) every 2 hours until the epithelium healed. After complete reepithelialization occurred, fluorometholone 0.1% eyedrops (Flucon威) were administered 5 times daily for the first month, 4 times daily for the second month, 3 times daily for the third month, twice daily for the fourth month, and once a day for the fifth and sixth months. In LASEK, the cornea was anesthetized with 5 drops of Novesin. The eye was prepared with povidone–iodine (Betadine威), and a plastic drape and lid speculum were applied. An 8.0 mm LASEK corneal trephine (Janach J2900) was used to create an epithelial incision. The corneal trephine is designed to create a 270-degree epithelial incision with a blunt section at 12 o’clock for the formation of a hinge. The blade was placed centrally on the visual axis; slight rotation of the blade was used to facilitate creation of the epithelial incision. An alcohol solution cone (Janach J2905) with an 8.5 mm diameter was placed on the eye. Twenty percent of the ethyl alcohol solution was instilled inside the alcohol solution cone and left for 25 to 30 seconds. The alcohol solution was then absorbed with a small surgical sponge. The area was thoroughly rinsed for 30 seconds with balanced salt solution (BSS威) and dried with a surgical sponge. An epithelial microhoe (Janach J2915A) was used to create the flap by lifting the edges of the epithelial incision. The epithelial flap was gently detached and folded at the 12 o’clock position. After laser ablation, the cornea was flooded with chilled (8°C) BSS for 20 to 30 seconds and the epithelial flap was carefully repositioned using a blunt spatula (Janach J2920A). The same type of therapeutic soft contact lens as in the PRK procedure was placed on the eye and the same topical eyedrops were instilled. The soft contact lens was removed 2 to 3 days after the procedure. The regimen of fluorometholone eyedrops used in the PRK eyes was used in most LASEK eyes. However, the regimen was individualized in 18 eyes based on a stable refraction, excellent visual acuity, and clear cornea and stopped at the end of the fifth month. The patients were examined on days 1 to 4 until the epithelium healed. The time required for complete epithelialization was recorded. The UCVA, BSCVA, and refraction were measured at 1 week and 1, 3, 6, 12, and 24 months. Subepithelial corneal haze levels were detected by slitlamp
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examination and graded from 0 to 4 according to Epstein and coauthors20 at 1, 3, 6, 12, and 24 months: 0, completely clear; 1, faint haze detectable only with broad tangential illumination; 2, discrete haze visible with difficulty by focal illumination and refraction possible; 3, moderately dense opacity partly obscuring iris detail; 4, severely dense opacity completely obscuring details of intraocular structures. At 1 week, patients were asked to complete a questionnaire about the pain they experienced using a 4-point scale: 0, no pain or discomfort; 1, mild burning, stinging, or mild pain; 2, moderate and more prolonged burning, stinging, or aching; 3, severe constant or sharp pain or aching that requires more analgesics to relieve. After 6 months, all patients were asked which procedure they preferred. The refractive surgical data for analysis and comparison adhered to published guidelines.21 Data from each patient were entered into Microsoft Excel (Office 97) to create a database and perform a statistical analysis of the 2 groups. An unpaired t test was used to compare the MSE refractions. The Mann-Whitney test was used to compare postoperative pain scores and corneal haze scores in the PRK and LASEK eyes. The Fisher exact test was used for analysis of categorized data. A P value less than 0.05 was considered significant.
Figure 1. (Autrata) Stability of refraction: The MSE refraction preoperatively and postoperatively.
Efficacy At 1 week, the mean UCVA was 0.64 ⫾ 0.21 in the PRK eyes and 0.87 ⫾ 0.23 in the LASEK eyes. The difference was statistically significant (P ⫽ .034). At 1 month and 1 and 2 years, the between-group differences in UCVA were not statistically significant (Table 2). The UCVA results at 24 months are shown in Table 3 and Figure 2. There were no statistically significant between-group differences in the mean UCVA or the efficacy index. The efficacy index (Table 4) was better in LASEK eyes (0.978) than in PRK eyes (0.967), but the difference was not significant (P ⫽ .78)
Results Refraction Preoperatively, the MSE manifest refraction was ⫺4.78 D ⫾ 2.93 (SD) (range ⫺2.0 to ⫺7.0 D) in the PRK eyes and ⫺4.90 ⫾ 3.01 D (range ⫺1.75 to ⫺7.50 D) in the LASEK eyes. The difference was not statistically significant (P ⫽ .69). At 2 years, the MSE manifest refraction was ⫺0.18 ⫾ 0.53 D (range ⫹0.50 to ⫺1.50 D) and ⫺0.23 ⫾ 0.46 D (range ⫹0.75 to ⫺1.25 D), respectively; the difference was not statistically significant (P ⫽ .83). The MSE manifest refraction preoperatively and postoperatively is shown in Table 1 and Figure 1.
Safety At 2 years, the mean BSCVA was 0.95 ⫾ 0.16 in the PRK eyes and 0.98 ⫾ 0.14 in the LASEK eyes. The safety index was 1.032 and 1.043, respectively (Table 5). This difference was not statistically significant. Four PRK eyes and no LASEK eye lost 1 Snellen line of BSCVA. The change in Snellen lines of BSCVA at 24 months is shown in Table 6 and Figure 3. Sixty-eight
Table 1. The MSE refraction preoperatively and postoperatively. MSE Refraction Postoperative (Mo) Group (n)
Preop
1
3
6
12
24
PRK (92)
⫺4.78 ⫾ 2.93
0.95 ⫾ 1.15
0.51 ⫾ 0.84
0.26 ⫾ 0.63
⫺0.23 ⫾ 0.59
⫺0.18 ⫾ 0.53
LASEK (92)
⫺4.90 ⫾ 3.01
0.81 ⫾ 0.95
0.39 ⫾ 0.71
0.18 ⫾ 0.48
⫺0.21 ⫾ 0.43
⫺0.23 ⫾ 0.46
⬎.05
⬎.05
⬎.05
⬎.05
⬎.05
⬎.05
P value
MSE ⫽ mean spherical equivalent; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
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Table 2. The mean UCVA postoperatively.
Table 4. Efficacy index (mean postop UCVA/mean preop BSCVA) at 24 months.
Mean UCVA Postoperatively Group (n)
1 Week
1 Month
1 Year
PRK (92)
0.64 ⫾ 0.21
0.78 ⫾ 0.22
0.88 ⫾ 0.17
LASEK (92)
0.87 ⫾ 0.23
0.89 ⫾ 0.18
0.91 ⫾ 0.20
⬍.05
⬎.05
⬎.05
P value
UCVA ⫽ uncorrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 3. Efficacy: UCVA at 24 months.
Mean Postop UCVA
Mean Preop BSCVA
Efficacy Index
PRK (92)
0.89 ⫾ 0.18
0.92 ⫾ 0.13
0.967
LASEK (92)
0.92 ⫾ 0.17
0.94 ⫾ 0.19
0.978
⬎.05
⬎.05
⬎.05
Group (n)
P value
UCVA ⫽ uncorrected visual acuity; BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 5. Safety index (mean postop BSCVA/mean preop BSCVA) at 24 months.
UCVA, n (%) Group (n)
20/20
20/25–20/40
>20/40
PRK (92)
62 (67)
20 (22)
10 (11)
LASEK (92)
67 (73)
17 (18)
8 (9)
⬎.05
⬎.05
P value
⬎.05
UCVA ⫽ uncorrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
PRK eyes (73.9%) had no change in BSCVA, 15 (16.3%) gained 1 line, and 5 (5.4%) gained 2 lines. Seventy-one LASEK eyes (77.1%) had no change in BSCVA, 18 (19.6%) gained 1 line, and 3 (3.3%) gained 2 lines. Predictability At 2 years, 62% of the LASEK eyes and 57% of the PRK eyes were within ⫾0.5 D of the desired refraction and 92% and 91%, respectively, were within ⫾1.0 D (Figure 4). There were no significant between-group
Mean Postop BSCVA
Mean Preop BSCVA
Safety Index
PRK (92)
0.95 ⫾ 0.16
0.92 ⫾ 0.13
1.032
LASEK (92)
0.98 ⫾ 0.14
0.94 ⫾ 0.19
1.043
⬎.05
⬎.05
⬎.05
Group (n)
P value
BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
Table 6. Safety: Change in Snellen lines of BSCVA at 24 months. Snellen Lines of BSCVA, n (%) 2 Lost
1 Lost
No Change
1 Gained
2 Gained
PRK (92)
0
4 (4.5)
68 (73.9)
15 (16.3)
5 (5.4)
LASEK (92)
0
0
71 (77.1)
18 (19.6)
3 (3.3)
Group (n)
P ⬎.05 BSCVA ⫽ best spectacle-corrected visual acuity; n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
differences. Three PRK eyes (3.2%) and 2 LASEK eyes (2.1%) were overcorrected 1.0 to 2.0 D. No eye in either group was overcorrected more than 2.0 D.
Figure 2. (Autrata) Efficacy: the UCVA at 2 years. 664
Haze At 1 month, the mean corneal haze score was 0.85 ⫾ 0.79 in PRK eyes and 0.52 ⫾ 0.64 in LASEK eyes, a statistically significant difference (P ⫽ .023). The difference was also significant at 3 months (P ⫽ .035) and 6 months (P ⫽ .028). The mean haze intensity then decreased, but the between-group difference was significant at 12 and 24 months (Figure 5 and Table 7). No
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Figure 3. (Autrata) Change in Snellen lines of BSCVA.
Postoperative Pain and Discomfort Based on the subjective questionnaire, the mean postoperative pain and discomfort scores were 1.82 ⫾ 1.34 in the PRK eyes and 1.06 ⫾ 0.90 in the LASEK eyes at 1 day; the difference was statistically significant (P ⫽ .019). The between-group differences at 2 and 3 days as well as overall were significant (Figure 6 and Table 8). The epithelial defect was completely healed by day 3 in the LASEK eyes and by day 5 in the PRK eyes. The mean epithelial healing time was 2.76 ⫾ 0.47 days (range 2 to 3 days) and 3.95 ⫾ 0.71 days (range 3 to 5 days), respectively. The difference was statistically significant (P ⫽ .033). Seventy-nine patients (86%) preferred the LASEK procedure because of less pain and discomfort, faster visual rehabilitation, and better visual acuity. There were no postoperative complications such as infection, recurrent erosion syndrome, or dry-eye problems. To date, no patient has required retreatment.
Discussion Figure 4. (Autrata) The refractive outcome (SE ⫽ spherical equivalent) at 24 months.
Figure 5. (Autrata) The mean corneal haze level postoperatively.
correlation between the haze scores and the refractive regression in PRK and LASEK eyes was found. The mean haze level differences between PRK and LASEK eyes were statistically significant. No significant between-group differences in the MSE refraction were found.
Over the past 2 years, investigators have reported advantages and encouraging results with LASEK. Lee et al.22 compared LASEK and PRK for the correction of myopia up to ⫺6.5 D in a prospective study of 27 patients with a 3-month follow-up. The results proved the efficacy and safety of LASEK. The incidence of postoperative pain and corneal haze was reduced in the LASEK eyes. Claringbold23 reported 12-month results in 222 consecutive eyes that had LASEK for myopia up to ⫺11.25 D. The study demonstrates that LASEK may be an excellent, effective, and safe alternative to LASIK for the surgical correction of myopia. Further prospective studies and a long-term evaluation should be done to confirm the role of LASEK in excimer laser refractive surgery. Our 2-year results of LASEK correction for myopia up to ⫺7.50 D indicate that the procedure may eliminate or reduce the complications of PRK and LASIK. Use of the epithelial flap decreased the time to epithelial healing. The reduced pain in LASEK eyes is probably because the epithelial flap acts as a biological therapeutic lens that protects the ablated stroma. The LASEK eyes achieved visual recovery sooner than the PRK eyes. At 1 week, the UCVA was better in the LASEK eyes than in
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Table 7. Mean corneal haze level. Postoperative (Mo) Mean Corneal Haze Group (n)
1
3
6
12
24
PRK (92)
0.85 ⫾ 0.79
1.14 ⫾ 0.63
1.06 ⫾ 0.52
0.54 ⫾ 0.31
0.43 ⫾ 0.29
LASEK (92)
0.52 ⫾ 0.64
0.73 ⫾ 0.51
0.61 ⫾ 0.40
0.35 ⫾ 0.28
0.21 ⫾ 0.24
.023
.035
.028
.038
.042
P value
n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy
prevalent in LASEK eyes than in PRK eyes during the entire follow-up. The specific underlying cellular events of less corneal stromal fibrosis or scarring after LASEK remain unclear. Various cytokines including keratinocyte growth factor and transforming growth factor  (TGF-) are known to regulate the corneal stromal wound-healing process after excimer laser keratectomy.24 –26 Among these cytokines, TGF- is proposed to be key in inducing corneal stromal fibrosis after excimer laser keratectomy. It has been shown that the increased expression of TGF- and TGF- receptors in keratocytes plays a role in the activation and proliferation of keratocytes and the production of extracellular matrix components, leading to corneal fibrosis after excimer laser keratectomy.24 It has been reported that the expression of TGF-1 in the keratocytes is lower after LASIK than after PRK. This indicates that the corneal stromal fibrosis regulated by TGF-1 is less after LASIK than after PRK.27 There may be a similar effect in the LASEK procedure, leading to decreased corneal stromal fibrosis. The epithelial flap repositioning may decrease the initial loss of anterior stromal keratocytes and late subepithelial fibroblast hyperplasia, which is similar to the effect of applying a human amniotic membrane after PRK.28 Laser-assisted subepithelial keratectomy can be used instead of LASIK in the case of a thin cornea and a large
Figure 6. (Autrata) The mean level of postoperative pain and discomfort.
the PRK eyes. The remaining epithelial flap acts as a smooth refractive surface, and this allows better initial visual acuity. In contrast to a previous report,22 the epithelial healing time was significantly lower with LASEK than with PRK. We believe that multizone ablation (for myopia greater than ⫺4.0 D), instillation of chilled BSS immediately after ablation, and, especially, epithelial flap repositioning may explain the elimination of early stromal haze in the LASEK eyes. The lack of late-onset corneal haze, even in eyes with moderate myopia up to ⫺7.5 D, is a promising aspect of LASEK. Corneal haze was less Table 8. Mean level of postoperative pain and discomfort.
Mean Postoperative Pain Group (n)
1 Day
2 Days
3 Days
Overall Level
PRK (92)
1.82 ⫾ 1.34
1.33 ⫾ 0.82
0.81 ⫾ 0.54
1.26 ⫾ 0.91
LASEK (92)
1.06 ⫾ 0.90
0.56 ⫾ 0.37
0.30 ⫾ 0.43
0.61 ⫾ 0.53
.019
.024
.0263
.0387
P value
n ⫽ number of eyes; PRK ⫽ photorefractive keratectomy; LASEK ⫽ laser-assisted subepithelial keratectomy Pain scale: 0 ⫽ no pain; 4 ⫽ severe pain
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correction, a small palpebral fissure or deep-set eye, or a neovascularized cornea due to incorrect contact lens use. In addition, LASEK should be considered the procedure of choice to reduce the risk of late flap trauma or dislocation. Laser-assisted subepithelial keratectomy may be a better method than LASIK for customized ablations. It may provide an improved flap–stromal interface that enhances the visual benefit provided by wavefront technology. The LASEK procedure requires more surgical training, but if creation of the epithelial flap is unsuccessful, the surgeon can easily convert to PRK. Further investigation is needed to evaluate LASEK for the correction of higher levels of myopia. We performed a study of LASEK in a group 58 patients with myopia of ⫺6.0 to ⫺10.0 D. The initial results of a 1-year follow-up are promising. In conclusion, our study demonstrated that LASEK can be an effective and safe method for the correction of low to moderate myopia up to ⫺7.5 D. It provided significantly quicker visual recovery and caused less haze than conventional PRK, and it eliminated post-PRK pain.
9.
10.
11.
12.
13. 14.
15.
16.
17.
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ing growth factor  superfamily and their receptors in the corneal stromal wound healing process after excimer laser keratectomy [letter]. Br J Ophthalmol 1998; 82:462– 463 25. Malley DS, Steinert RF, Puliafito CA, Dobi ET. Immunofluorescence study of corneal wound healing after excimer laser anterior keratectomy in the monkey eye. Arch Ophthalmol 1990; 108:1316 –1322 26. Wilson SE, Walker JW, Chwang EL, He Y-G. Hepatocyte growth factor, keratinocyte growth factor, their receptors, fibroblast growth factor receptor-2, and the cells of the cornea. Invest Ophthalmol Vis Sci 1993; 34:2544 –2561 27. Kaji Y, Soya K, Amano S, et al. Relation between corneal haze and transforming growth factor-1 after photore-
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fractive keratectomy and laser in situ keratomileusis. J Cataract Refract Surg 2001; 27:1840 –1846 28. Choi YS, Kim JY, Wee WR, Lee JH. Effect of the application of human amniotic membrane on rabbit corneal wound healing after excimer laser photorefractive keratectomy. Cornea 1998; 17:389 –395 From the Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. Presented in part at the XIX Congress of the European Society of Cataract & Refractive Surgeons, Amsterdam, The Netherlands, September 2001. Supported by the University Hospital Brno, Brno, Czech Republic. Neither author has a financial or proprietary interest in any product mentioned.
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