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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 20  |  Issue : 1  |  Page : 104-112

Assessment of post-LASIK flap thickness created by mechanical microkeratomes by anterior segment optical coherence tomography


1 Faculty of Medicine, Al-Azhar University, Assiut, Egypt
2 Department of Ophthalmology, Faculty of Medicine, Al-Azhar University, Assiut, Egypt

Date of Submission21-Sep-2021
Date of Decision03-Nov-2021
Date of Acceptance09-Nov-2021
Date of Web Publication4-Mar-2022

Correspondence Address:
MBBCh Islam A.M Amr
Faculty of Medicine, Al-Azhar University, Assiut, 71511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/azmj.azmj_116_21

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  Abstract 


Background and aim Laser-assisted in situ keratomileusis (LASIK) is the most popular refractive surgical operation for the correction of myopia, hyperopia, and astigmatism. Corneal flap creation is an essential step for the success of LASIK. The aim of the work is to evaluate the accuracy of the post-LASIK flap thickness created by mechanical microkeratomes using Anterior segment optical coherence tomography (ASOCT).
Patients and methods This study included 60 eyes (of 30 patients), who underwent LASIK for refractive error correction. The patients were divided into two groups: (a) group A involved 30 eyes of 15 patients; in this group, the mechanical microkeratome Moria M2 (Moria M2, 110) was used. (b) Group B involved 30 eyes of 15 patients; in this group, the microkeratome Moria M2 (Moria M2, 100 with medlogic plano head) was used.
Results As regards postoperative changes in flap thickness, the results of the current study showed that there were no considerable changes in thickness of the flap between 1 week, 1 month, 3 months, and 6 months postoperatively in either group.
Conclusion Moria M2 100 with medlogic plano head created LASIK flaps with thinner thickness, and more predictability and more preservation of bed thickness than those created with the Moria M2 110.

Keywords: laser-assisted in situ keratomileusis flap, mechanical microkeratomes, optical coherence tomography


How to cite this article:
Amr IA, Yousef HS, Ahmed AN. Assessment of post-LASIK flap thickness created by mechanical microkeratomes by anterior segment optical coherence tomography. Al-Azhar Assiut Med J 2022;20:104-12

How to cite this URL:
Amr IA, Yousef HS, Ahmed AN. Assessment of post-LASIK flap thickness created by mechanical microkeratomes by anterior segment optical coherence tomography. Al-Azhar Assiut Med J [serial online] 2022 [cited 2022 Jun 29];20:104-12. Available from: http://www.azmj.eg.net/text.asp?2022/20/1/104/339062




  Introduction Top


Laser-assisted in situ keratomileusis (LASIK) is a rapid, easy, pain-free procedure with faster sight recovery and reduced incidence of subepithelial haziness as in PRK [1]. Corneal flap creation is an essential phase for the success of LASIK [2], and there are many ways to generate the corneal flap by the femtosecond laser or mechanical corneal flap. Mechanical microkeratomes create the flap (199) by an oscillating blade and shearing force transmitted through the corneal stroma, while ultrashort laser pulses are used by femtosecond laser systems and make corneal tissue cuts by the photodisruption process [3]. The danger of complications during surgery is increased when mechanical microkeratome is used to make the corneal flap, such as irregular flaps, free flaps, incomplete flaps, and torn flaps [4]. The ideal flap is thin (average 100 μm), stable, uniform, central, with no wrinkles [3]. Thin flaps are now critical, leaving more stromal layers, and reducing the incidence of post-LASIK ectasia. But very thin flaps are more prone to complications such as an irregular, incomplete, free flap, loophole, torn flap, or the displaced flap. The femtosecond laser has helped this new strategy create thinner plates within better predictability, and such less complications [5]. Various microkeratomes can be used to make the corneal flap. The Moria M2 (Moria) is a compact and commonly used disposable autohead with a mechanical stop designed for safety [6]. Many studies found significant differences in flap thickness created by different mechanical microkeratomes [7]. Anterior segment optical coherence tomography (ASOCT) can facilitate the diagnosis and recording of corneal conditions such as degeneration, various inflammatory diseases, and atrophy. ASOCT can be used to diagnose and treat ulcers, corneal infiltrates, pricking, or scarring [8]. ASOCT is now the most widely used corneal imaging system, not only to assess flap thickness after LASIK, but also to assess flap morphology and determine the lateral cut angle at the interface of the flap margin [9].

The aim of the work is to evaluate the accuracy of the post-LASIK flap thickness created by mechanical microkeratomes using ASOCT.


  Patients and methods Top


The research was conducted on Al-Nahar Eye Surgery Center in Assiut.

Research design: prospective research.

Patients

The current research was conducted on 60 eyes (of 30 patients), who underwent laser refractive error correction.

The patients were divided into two groups:
  1. Group A: included 30 eyes of 15 patients. In this set, the Moria M2 microkeratome (Moria M2, 110; Anthony, France) was used.
  2. Group B: included 30 eyes of 15 patients. In this set, the microkeratome Moria M2 (Moria M2, 100 within the medlogic plano head) was used.


Inclusion criteria

  1. Age from 20 to 50 years.
  2. Scan the appearance of the cornea on the slit lamp.
  3. Normal lens, normal intraocular pressure, and normal fundus examination results.
  4. Spherical error from hyperopia + 4 D to −10 D myopia.
  5. Refractive astigmatism from +4 D to −4 D astigmatism.


Exclusion criteria

  1. Corneal diseases such as inflammation and dystrophies.
  2. Abnormal lenses (cataracts, subluxation, aphakia, etc.) abnormal posterior segment.
  3. Spherical error more than +4 or more than −10 myopia.
  4. Astigmatism more than +4 excessive astigmatism or more than −4 myopic astigmatism.
  5. Patients under 20 years of age or more than 50 years of age.
  6. Noncompliant patient.


Methodology

All patients were subjected to the following:


  1. History
    • Systemic: (a) patients were asked about their previous general medical history [2]. Patients were asked about their status in relation to pregnancy, breastfeeding, use of oral contraceptives, or use of hormone replacement therapy. Ocular: patients were asked about their ocular history regarding ophthalmic medical and surgical history, history of contact lens use, trauma, and use of eye drops. History of use of eyeglasses and variations in previous prescriptions in the past year.


  2. Clinical examination:
    1. Vision: visual acuity of patients were measured and their refraction, both manifest and cycloplegic, were also measured.
    2. External examination, slit-lamp examination, intraocular pressure measurement, and fundus examination to exclude any intraocular or extraocular pathology.
    3. Ocular motility and assessment of phorias and tropias, confrontational visual field test.


  3. Investigations:
    • Corneal topography and corneal thickness were measured by the Scheimpflug Camera Pentacam, CSO (Costruzione strumenti oftalmici), Firenze, Italy.


  4. Operative technique:
    1. Immediate preoperative counseling:
      • Before starting treatment, patients were instructed about what to expect during the procedure, that is the sounds, smells, and steps taken. Anxious patients were given oral analgesics.
    2. Preoperative medications:
      • Surgery were performed under topical anesthesia. Benoxinate 4% (Benox ED) eye drops were instilled three times, 5 min apart. Povidone–iodine 10% was used for the preparation of the skin. Povidone–iodine 5% drops were applied to the ocular surface, left for 30 s, then irrigated. A sterile drape was placed over the skin and eyelashes ([Figure 1]).
      Figure 1 Devices used in LASIK surgeries: (a) M2 110 microkeratome metallic head. (b) Med logic plano head 100 microkeratome. (c) The M2 single-use mechanical microkeratome. (d) Moria motor adaptor microkeratome evolution 3. LASIK, laser-assisted in situ keratomileusis.

      Click here to view
    3. Operative details:
      • The procedure first began by numbing the corneal surface, by the balanced salt solution for irrigation, and drying the epithelium within the cellulose sponge. The standard LASIK marker was used to distinguish the cornea. All procedures were performed first on the right eye, and then on the left eye, by the same blade. For the right eye, the incision was made from the temporal and inferior side to the nasal side, and for the left eye, the incision was made from the nasal side to the temporal side. A Moria, M-2 microkeratome (Antony, France, SN 8862) was used to make the flap within either the m2 110 µm head or the m2 100 µm with medlogic plano head. The suction ring has been applied. Then the cuff was placed over the piece and fixed in place. Then the blade was pushed forward, then back, and the blade was released. The microkeratome was removed, and the flap was reversed. Stromal ablation was applied. The blown layer was then dried to remove tissue residues, and then irrigated. The cap was put back in place, the front was irrigated again, the flap was repositioned according to the alignment marks, and allowed to dry for 2 min.
    4. Topical antibiotic (Moxifloxacin 0.5% Vigamox ED) and steroids (Predinsolone 1% Optipred ED) were applied.
      • All cases were operated within an Bausch& Lomb Teneo 317 model 2 excimer laser (Bausch& Lomb, London, England, SN IEC 60825-1.2014). All LASIK flaps were created within the Moria-2 keratoplasty by either the 110 µm head or the 100 µm tip within the medlogic plano tip.
    5. Postoperative regimen:
      • Steroids and antibiotics were applied for 1 week and then discontinued, and lubricants were used for 3 months.
    6. Postoperative measurements:
      • All eyes were evaluated by Topcon ASOCT 3D OCT-2000 FA Plus, Tokyo, Japan − SN 789079 at 1 week, 1 month, 3 months, and 6 months after surgery. The thickness of each flap was measured at three points (center and nose 2 mm and temporal 2 mm from the corneal apex) ([Figure 2]).
Figure 2 Topcon 3D OCT-2000 series.

Click here to view


Ethical consideration

All participants in the current study were informed of the nature and details of the current work, and written consent was obtained for each participant. The study was approved by the local ethics committee, Assiut College of Medicine and Al-Azhar University. The study is conducted in accordance with Helsinki standards as revised in 2013.

Statistical analysis

Information was tested by the Statistical Software for the Social Sciences (SPSS), version 18.0. Quantitative information were represented as refer to ±SD. Qualitative information was represented as frequency and percentage.


  Results Top


Our research results showed highly statistically distinguished difference (P<0.001) among the examined groups as regards OD CFT, OD 2 mm N, OD 2 mm T, OS CFT, OS 2 mm N, and OS 2 mm T at postoperative 1 week, and at 1, 3, and 6 months.

Among group A, at 1 week postoperative, the refer to thicknesses of the flap in OD were 136.4±11.5 μm at the center, 135.7±11.4 μm at 2 mm nasal, and 135.4±11.3 μm at 2 mm temporal. In OS, the refer to thicknesses of the flap were 134.1±10.7 μm at center, 133.2±10.3 μm at 2 mm nasal, and 133.3±10.5 μm at 2 mm temporal. At 1 month postoperative, the refer to thicknesses of the flap in OD were 134.4±11.2 μm at center, 133.5±11.2 μm at 2 mm nasal, and 133.5±11.1 μm at 2 mm temporal. In OS, the flap thicknesses were 132.2±11.2 μm at center, 131.7±10.9 μm at 2 mm nasal, and 131.7±10.8 μm at 2 mm temporal. At 3 month postoperative, the refer to flap thicknesses in OD were 134.4±11.3 μm at center, 133.5±11.3 μm at 2 mm nasal, and 133.6±11.2 μm at 2 mm temporal. In OS, the refer to flap thicknesses were 132.3±11.3 μm at center 131.8±11 μm at 2 mm nasal, and 131.9±11 μm at 2 mm temporal. At 6 month postoperative, the refer to thicknesses of the flap in OD were 134.5±11.5 μm at center, 133.7±11.6 μm at 2 mm nasal, and 133.6±11.4 μm at 2 mm temporal. In OS, the refer to flap thicknesses were 132.4±11.4 μm at center, 132.0±11.1 μm at 2 mm nasal, and 131.9±11.1 μm at 2 mm temporal.

Among group B, at 1 week postoperative, the refer to flap thicknesses in OD were 118.5±8.6 μm at center, 117.9±8.8 μm at 2 mm nasal, and 117.9±8.7 μm at 2 mm temporal. In OS, the flap thicknesses were 116.1±8.8 μm at center, 116.0±8.9 μm at 2 mm nasal, and 115.6±8.8 μm at 2 mm temporal. At 1 month postoperative, the refer to flap thicknesses in OD were 116.9±8.3 μm at center, 116.7±8.2 μm at 2 mm nasal, and 116.4±8.4 μm at 2 mm temporal. In OS, the flap thicknesses were 114.3±8.5 μm at center, 114.0±8.1 μm at 2 mm nasal, and 114.1±8.1 μm at 2 mm temporal. At 3 month postoperative, the refer to flap thicknesses in OD were 117±8.1 μm at center, 116.6±8 μm at 2 mm nasal, and 116.3±8.1 μm at 2 mm temporal. In OS, the refer to flap thicknesses were 114.2±8.1 μm at center, 113.8±8.1 μm at 2 mm nasal, and 114.0±8.1 μm at 2 mm temporal. At 6 month postoperative, the refer to flap thicknesses in OD were 117.0±8.6 μm at center, 116.7±8.4 μm at 2 mm nasal, and 116.3±8.6 μm at 2 mm temporal. In OS, the refer to flap thicknesses were 114.4±8.7 μm at center, 114.0±8.2 μm at 2 mm nasal, and 114.2±8.32 mm at 2 mm temporal.

The results of clinical assessment, laboratory, and radiological findings are tabulated and statistically analyzed as follows:

[Table 1] explains no statistically distinguished difference (P>0.05) among the examined groups as regards age and sex.
Table 1 Comparison among the examined groups as regards age and sex

Click here to view


[Table 2] explains: no statistically distinguished difference (P>0.05) among the examined groups as regards OD K1, OS, K1, OS K2, OD sphere, OD cylinder, OD CCT, OS CCT, and OS UCVA. There was statistically distinguished difference (P<0.05) among the examined groups as regards OD K2 and OS cylinder. There was highly statistically distinguished difference (P<0.001) among the examined groups as regards OS sphere and OD UCVA.
Table 2 Comparison among the examined groups as regards preoperative information

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[Table 3] explains: there was no statistically distinguished difference (P>0.05) among the examined groups as regards 1 week postoperative OD UCVA, OS UCVA, OD BCVTHE, and OS BCVA. There was highly statistically distinguished difference (P<0.001) among the examined groups as regards 1 week postoperative OD CFT, OD 2 mm N, OD 2 mm T, OS CFT, OS 2 mm N, and OS 2 mm T.
Table 3 Comparison among the examined groups as regards 1-week postoperative information

Click here to view


[Table 4] explains: no statistically distinguished difference (P>0.05) among the examined groups as regards 1-month postoperative OD UCVA, OS UCVA, OD BCVTHE, and OS BCVA. There was highly statistically distinguished difference (P<0.001) among the examined groups as regards 1 month postoperative OD CFT, OD 2 mm N, OD 2 mm T, OS CFT, OS 2 mm N, and OS 2 mm T.
Table 4 Comparison among the examined groups as regards 1 month postoperative information

Click here to view


[Table 5] explains: no statistically distinguished difference (P>0.05) among the examined groups as regards 3 months postoperative OD UCVA, OS UCVA, OD BCVTHE, and OS BCVA. There was highly statistically distinguished difference (P<0.001) among examined groups as regards 3 months postoperative OD CFT, OD 2 mm N, OD 2 mm T, OS CFT, OS 2 mm N, and OS 2 mm T.
Table 5 Comparison among the examined groups as regard 3-month postoperative information

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[Table 6] explains: no statistically distinguished difference (P>0.05) among the examined groups as regards 6 months postoperative OD UCVA, OS UCVA, OD BCVTHE, and OS BCVA. There was highly statistically distinguished difference (P<0.001) among the examined groups as regards 6 months postoperative OD CFT, OD 2 mm N, OD 2 mm T, OS CFT, OS 2 mm N, and OS 2 mm T ([Figure 3] and [Figure 4]).
Table 6 Comparison among the examined groups as regards 6-month postoperative information

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Figure 3 Some pictures of ASOCT of flap thickness M2 110.

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Figure 4 Some pictures of ASOCT of flap thickness M2 100 with med logic plano head.

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  Discussion Top


Our research was implemented on 60 eyes (of 30 patients), who underwent laser in-situ keratomileusis for refractive error correction.

There were 26.4±11.5 and 18.5±8.6 µm thicker than the intended thickness in group A and group B, respectively. The achieved central flap thickness difference from the intended thickness showed statistically distinguished values among the two groups. The results show higher flap accuracy and reproducibility in group B compared with group A.

In Karabelthe et al. [10], 72 (37 right eyes and 35 left eyes) consecutive LASIK procedures conducted on 37 patients (20 females and 17 males) for myopia and/or myopic astigmatism were evaluated. The Moria M2 single-use head 90 microkeratome was used to generate the superior hinged flap. The central thickness of the cornea was measured in all eyes. The thicknesses of the flaps were 131.2±19.5 µm (91–192 µm), 136.97±20.07 µm (106–192 µm), and 134.16±19.85 µm (91–192 µm) in the left, right, and both eyes, respectively. They concluded that the Moria M2 single-use head 90 microkeratome cut relatively thicker flaps than were intended.

Mimouni et al. [11] included 6242 eyes of 3121 patients. Bilateral laser in situ keratomileusis (LASIK) was applied by either an SBK-90 microkeratome head for group A or an M2-90 microkeratome head for group B. Group A included 2560 (41%) eyes, and group B involved 3682 (59%) eyes. The refer to age of the patient were 32.2±9.8 years (SD); 1648 (52.8%) patients were men and 1473 (47.2%) were women. Distinguished thinner flaps were resulted in the eyes in group A compared with the eyes in group B (108.9±15.3 and 118.4±22.7 mm, respectively, P<0.001).

Azzam et al. [12] performed the prospective clinical research involving 60 eyes of 30 patients. They were classified into three groups (20 eyes in each group). The corneal flaps were treated with the Moria SBK device, the Alcon Wavelight FS-200 FS laser, or the Moria MK laser. ASOCT was performed 1 month after surgery to assess the central flap thickness and lateral cut angle. The refer to cutoff angle of error was −39.00±19.00, 24.75±12.56, and 25.65±10.31° in the SBK, FS, and MK groups, respectively (P<0.001). The refer to variances among the intended and achieved flap thickness were 16.25±29.73 μm in the MK group, −1.20±6.86 μm in the FS group, and 1.50±8.06 μm in the SBK group (P=0.340). There were marked variances among the three groups with regard to the intended and achieved lateral cutoff angle. Flap thickness were more predictable in the SBK and FS groups, with little discrepancy among the intended and achieved flap thickness, while in the MK group, the difference was statistically distinguished.

The results of the current research showed that there were no statistical significance in the thickness of the corneal flap among the right and left eye in either group.

According to the current research, Karabelthe et al. [10] found that there is no difference among the right and left eye. The refer to flap thicknesses were 136.97±20.07 μm (range: 106–192 μm) at right, 131.2±19.5 μm (range: 91–192 μm) at left, and 134.16±19.85 μm (range: 91–192 μm) in both eyes. Also, Chen et al. performed [14] bilateral LASIK in 54 eyes (27 patients) by the single-use Moria M2 head and the slice thickness was assessed to be 155.6±14.8 μm in the right eye and 151.6±12.5 μm in the left eye.

In contrast to our results, Mimouni et al. [11] observed that the right eye has a thicker corneal flap than the left eye (P<0.000). The refer to values in the right eye were 110.1±15.2 mm in group A and 107.6±15.4 mm in group B and in the left eye, 122.6±22.8 and 114.2±21.9 mm, respectively.

Regarding postoperative variations in flap thickness, the results of the current research showed that there were no distinguished variations in flap thickness among 1 week and 1 month and 3 months and 6 months after surgery in either group. These results were supported by Hu et al. [13] in that the flap thicknesses measured by ASOCT at seven points in the 7 mm diameter are 1 week and 1 month after surgery in 115 patients undergoing LASIK. There are no distinguished variations in flap thickness between 1 week and 1 month after surgery.

Limitation of the study

Sample profile: Caucasian (Egyptian) population only.

Time: time-dependent changes in flap thickness and bed thickness may vary with years.


  Conclusion Top


From our research we concluded that:

LASIK plates created within Moria M2 100 within the medlogic plano head have lesser thickness and greater predictability and preservation of bed thickness than those created with Moria M2 110.

Recommendations

From our study, we recommend the use of Moria M2 100 with medlogic plano head with all patients in LASIK procedure due to its thinner thickness, and more predictability and more preservation of bed thickness than the Moria M2 110.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Sutton GL, Kim P. Laser in situ keratomileusis in 2010-the review. Clin Exp Ophthalmol 2010; 38:192–210.  Back to cited text no. 1
    
2.
Salomao MQ, Wilson SE. Femtosecond laser in laser insitukeratomileusis. J Cataract Refract Surg 2010; 36:1024–1032.  Back to cited text no. 2
    
3.
Espandar L, Meyer J. Intraoperative and postoperative complications of laser in situ keratomileusis flap creation by intralase femtosecond laser and mechanical microkeratomes. Middle East Afr J Ophthalmol 2010; 17:56–59.  Back to cited text no. 3
    
4.
Al-Mezaine HS, Al-Amro SA, Al-Obeidan S. Intraoperative flap complications in laser in situ keratomileusis within two types of microkeratomes. Saudi J Ophthalmol 2011; 25:239–243.  Back to cited text no. 4
    
5.
Zhou Y, Tian L, Wang N, Dougherty PJ. Anterior segment optical coherence tomography measurement of LASIK flaps: femtosecond laser vsmicrokeratome. J Refract Surg 2011; 27:408–416.  Back to cited text no. 5
    
6.
Kanellopoulos AJ, Asimellis G. Three dimensional LASIK flap thickness variability: topographic central, paracentral and peripheral assessment in flaps created by dimensional LASIK the mechanical microkeratome(M2) and two different femtosecond lasers (FS60 and FS200). Clin Ophthalmol 2013; 7:675–683.  Back to cited text no. 6
    
7.
Aslanides IM, Tsiklis NS, Astyrakakis NI, Pallikaris LG, Jankov MR. LASIK flap characteristics by the Moria M2 microkeratome within the 90-microm single use head. J Refract Surg 2007; 23:45–49.  Back to cited text no. 7
    
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Dua HS, Sinha R, D’Souza S, Potgieter F, Ross A, Kenaway M, Scott I, Said DG. Descemet membrane detachment: the novel concept in diagnosis and classification. Am J Ophthalmol 2020; 218:84–98. ‏  Back to cited text no. 8
    
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Ahn H, Kim JK, Kim CK, Han GH, Seo KY, Kim EK, Kim T-I. Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and the microkeratome. J Cataract Refract Surg 2011; 37:349–357.  Back to cited text no. 9
    
10.
Karabelthe Y, Muftuoglu O, Kaythe F. Corneal flap thickness within the Moria M2 single-use head 90 microkeratome in 72 consecutive LASIK procedures. Clin Ophthalmol 2017; 11:487.  Back to cited text no. 10
    
11.
Mimouni M, Vainer I, Assad N, Nemet A, Selthe T, Munzer G et al. Incidence, indications, and outcomes of eyes needing early flap lifting after LASIK. Cornea 2018; 37:1118–1123.  Back to cited text no. 11
    
12.
Azzam S, Hosny M, Chehab Z, Anis M. Flap thickness and side-cut angle by sub-Bowman keratomileusismicrokeratome, 200-kHz femtosecond laser system, and Moria M2 microkeratome. Delta J Ophthalmol 2020; 21:242.  Back to cited text no. 12
    
13.
Hu YQ, Ye XY, Zhou XL, Li Y, Xu CH, Tian L-L., Zhu H, Sheng YH. Practical method to calculate post-LASIK corneal power: the Actual Ka+ p method. Int J Ophthalmol 2010; 3:337.  Back to cited text no. 13
    
14.
Chen HJ, Xia YJ, Zhong YY, Song XL, Chen YC. Anterior segment optical coherence tomography measurement of flap thickness after myopic LASIK using Moria one use plus microkeratome. J Refract Surg 2010; 26:403–410.  Back to cited text no. 14
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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