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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 17  |  Issue : 1  |  Page : 1-8

Combined cross-linking with femtosecond laser Myoring implantation versus combined cross-linking with femtosecond laser Keraring implantation for treatment of keratoconus


Department of Ophthalmology, Sohag University Hospital, Sohag University, Sohag, Egypt

Date of Submission13-May-2015
Date of Acceptance26-Aug-2015
Date of Web Publication16-Mar-2016

Correspondence Address:
Mohammed I Hafez
Department of Ophthalmology, Sohag University Hospital, Sohag University, Sohag 82425
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-9173.178760

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  Abstract 

Purpose
The aim of this study was to compare the results with regard to efficacy, safety, and patient satisfaction between two combined procedures: combined femtosecond laser Myoring implantation with cross-linking (CXL) and combined femtosecond laser Keraring implantation with CXL for treatment of keratoconus.
Setting
This study was conducted in Sohag University Hospital, Sohag University, Egypt, in association with Sohag Future Femtosecond Laser Center.
Design
This was a prospective nonrandomized clinical comparative study.
Patients and methods
A total of 46 eyes of 30 patients with keratoconus were included in this study.
Group A included 27 eyes of 17 patients who were subjected to combined CXL with femtosecond laser Myoring implantation, and group B included 19 eyes of 13 patients who were subjected to combined CXL with femtosecond laser Keraring implantation. All eyes were subjected to preoperative and postoperative uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest refraction, slit lamp examination of anterior segment, intraocular pressure, fundus examination, and keratometry and pachymetry assessment with Pentacam corneal topographies at 3 and 6 months of follow-up.
Results
In group A, the preoperative mean ± SD UCVA was 1.30 ± 0.28 (logMAR), whereas the postoperative mean UCVA was 0.90 ± 0.12. The preoperative mean BCVA was 0.70 ± 0.23, whereas the postoperative mean BCVA was 0.30 ± 0.17. The preoperative keratometric average ± SD was 53.27 ± 0.62 D, whereas the postoperative keratometric average was 45.83 ± 0.64 D. The postoperative astigmatic correction was 1.51 ± 0.42 D. In group B, the preoperative mean UCVA was 1.30 ± 0.33, whereas the postoperative mean UCVA was 1 ± 0.16. The preoperative mean BCVA was 0.90 ± 0.46, whereas the postoperative mean BCVA was 0.60 ± 0.32. The preoperative keratometric average was 50.97 ± 0.48, whereas the postoperative keratometric average was 49.01 ± 0.32. The postoperative astigmatic correction was 3.07 ± 0.15.
Conclusion
This study proved that combined CXL with Myoring implantation is effective in the correction of the myopic component of keratoconus. Combined CXL with Keraring implantation is effective in the correction of the astigmatic component in keratoconus. The type and the site of keratoconus cone together with the K readings can help in the preoperative decision of which type of ring is best in each keratoconus case. This study proved that there is a synergistic action when CXL is combined with intracorneal rings (Myoring or Keraring).

Keywords: cross-linking, femtosecond laser, Keraring, keratoconus, Myoring


How to cite this article:
Hafez MI. Combined cross-linking with femtosecond laser Myoring implantation versus combined cross-linking with femtosecond laser Keraring implantation for treatment of keratoconus. Delta J Ophthalmol 2016;17:1-8

How to cite this URL:
Hafez MI. Combined cross-linking with femtosecond laser Myoring implantation versus combined cross-linking with femtosecond laser Keraring implantation for treatment of keratoconus. Delta J Ophthalmol [serial online] 2016 [cited 2017 Oct 23];17:1-8. Available from: http://www.djo.eg.net/text.asp?2016/17/1/1/178760


  Introduction Top


Keratoconus is an asymmetric, bilateral, progressive, and noninflammatory ectasia due to gradual biomechanical instability of the cornea. Its reported frequency is approximately one in 2000 in the general population. The condition usually begins at puberty and progresses in ~20% of patients to such an extent that penetrating keratoplasty becomes necessary to preserve vision [1].

Implantation of corneal ring segments into a circular corneal tunnel improves visual acuity and reduces central corneal steepening in keratoconus. A new surgical system referred to as the corneal intrastromal implantation system (CISIS), in which the Myoring flexible full-ring implant is inserted into a corneal pocket, proved effective in the treatment of high myopia and keratoconus [2].

Keraring is an intracorneal ring segment (ICRS) that is used to treat keratoconus. It acts by regularizing the anterior corneal surface, thus decreasing myopia and regular and irregular astigmatism. They are available in different arc lengths and are made of polymethylmethacrylate. They are triangular in cross-section in contrast to other ICRS such as Ferrara rings, and they have a 600-μm base and an apical diameter of 5 mm. Ferrara rings are also hexagonal in cross-section but INTACS are oval in cross-section.

Myoring is a 360° continuous full-ring implant to be implanted into a corneal pocket for the treatment of myopia and keratoconus. The internationally patented device combines two contradictory qualities: rigidity for the modeling and stabilization of the corneal shape after implantation, and flexibility (shape memory) for the implantation through a small pocket entry to preserve the corneal biomechanics. The nomogram for the selection of the right Myoring dimension for keratoconus is very simple and depends only on the value of the central K average-reading according to SIM K1 +SIM K2/2 [3].

Femtosecond laser technology allows the surgeon to program a corneal stromal dissection at a predetermined depth with an extremely high degree of accuracy, thus avoiding the potential inaccuracies of a mechanical dissection that is dependent on the surgeon's manual skills [4].

Corneal collagen cross-linking (CXL) strengthens the stromal collagen fibrillae of the cornea, halting and stabilizing the evolution of keratoconus with a long-term increase in corneal biomechanical rigidity. CXL stiffens the human cornea by ∼500%, increases the collagen fiber diameter by 12.2%, and induces the formation of high-molecular-weight collagen polymers, with a remarkable chemical stability [1].


  Patients and methods Top


The aim of this study was to compare combined CXL with femtosecond laser Myoring implantation (DIOPTEX GmbH, Linz, Austria) and combined CXL with femtosecond laser Keraring (Mediphacos Inc., Belo Horizonte, Brazil; http://www.mediphacos.com/en/produtos_implanteIntraEstromalKeraring.asp) implantation for the treatment of keratoconus to understand which ring is suitable in which keratoconus stage and cone properties.

The design of this study was a prospective nonrandomized interventional comparative clinical trial that was performed in Sohag University Hospital (Egypt) after the approval of the ethical committee and written consent was obtained from the patients after full explanation of the procedure for the treatment of keratoconus and the nature of their disease.

Forty-six eyes of 30 patients with keratoconus were treated with intracorneal ring (ICR) implantation (Myoring or Keraring) combined with CXL to correct the refractive components (myopic or astigmatic) of keratoconus. The studied eyes were divided into two groups:

  1. Group A included 27 eyes of 17 patients who were subjected to combined CXL with femtosecond laser Myoring (DIOPTEX GmbH) implantation.
  2. Group B included 19 eyes of 13 patients who were subjected to combined CXL with femtosecond laser Keraring (Mediphacos Inc.) implantation.


All eyes were subjected to the following preoperative and postoperative measures:

  1. Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA).
  2. Manifest and cycloplegic refraction.
  3. Slit lamp examination of anterior segment.
  4. Intraocular pressure and fundus examination.
  5. Pentacam (OCULUS, Arlington Washington, USA): keratometry and pachymetry were assessed using corneal topographies at 3 and 6 months of follow-up.
  6. Anterior segment optical coherent topography (OCT) to assist the depth of the rings.


Surgical procedure

The following devices were used in this study:

  1. The KXL System (Avedro, Waltham, Massachusetts, USA) accelerated CXL [Figure 1].
    Figure 1: The cross-linking CXL System (Avedro).

    Click here to view
  2. Advanced femtosecond laser (iFS; Abbott, Chicago, Illinois, USA) [Figure 2]a. [Figure 2]b shows the appearance of the femtosecond laser during descend of the patient interface (or the cone) onto the suction ring.
    Figure 2: (a) Advanced femtosecond laser (iFS; Abbott), and (b) application of the patient interface or cone of the femtosecond laser onto the suction ring.

    Click here to view


Combined cross-linking with femtosecond laser Myoring implantation

The intraoperative parameters of the devices were as follows:

  1. Femtosecond laser parameters for the corneal pocket were as follows: diameter, 9 mm; depth, 300 μm; incision site, at the temporal side of the eye; incision diameter, 5-6 mm according to the ring; and width of the pocket, 8 mm.
  2. Pocket CXL injection of riboflavin (Vibex Xtra, Avedro, Waltham, Massachusetts, USA) in the pocket every 1 min for 5 min, followed by 8 min accelerated CXL using the pulsed mode with 30 mW/cm 3 power.


The first step to start with was application of the suction ring onto the cornea [Figure 3]a. [Figure 3]b shows the creation of the corneal pocket with femtosecond laser. [Figure 3]c shows the creation of the opening incision site of the pocket at the temporal side. [Figure 3]d shows gentle opening of the corneal pocket was made with a spatula. [Figure 3]e shows ensuring complete opening of the pocket. [Figure 3]f shows injection of riboflavin (Vibex Xtra) into the pocket. [Figure 3]g shows pocket CXL using accelerated pulsed mode. [Figure 3]h shows the remaining riboflavin was washed from the pocket with BSS.
Figure 3: Combined cross-linking (CXL) with femtosecond laser Myoring implantation: (a) application of the suction ring; (b) creation of the corneal pocket with femtosecond laser; (c) creation of the opening incision site of the pocket at the temporal side; (d) gentle opening of the corneal pocket with a spatula; (e) using a spatula to ensure complete opening of the pocket; (f) injection of ribofl avin (Vibex Xtra) into the pocket; (g) pocket CXL using accelerated pulsed mode; (h) washing the remaining ribofl avin from the pocket with BSS

Click here to view


Ensuring the correct position of the Myoring [Figure 4]a, the Myoring was introduced into the pocket [Figure 4]b. The Myoring was pushed centrally [Figure 4]c, and the correct position of the Myoring inside the pocket was examined [Figure 4]d. The Myoring was adjusted centrally within the corneal pocket [Figure 4]e and the contact lens was applied [Figure 4]f.
Figure 4: Combined cross-linking with femtosecond laser Myoring implantation: (a) ensuring the correct position of the Myoring; (b) introducing the Myoring into the pocket; (c) pushing the Myoring centrally; (d) examination of the correct position of the Myoring inside the pocket; (e) adjustment of the Myoring centrally within the corneal pocket; (f) contact lens application.

Click here to view


Combined cross-linking with femtosecond laser Keraring implantation

The intraoperative parameters of the devices were as follows:

  1. Epithelium-on CXL: dropping of riboflavin (ParaCel, Avedro, Waltham, Massachusetts, USA) on the cornea every 1.5 min for 4.5 min was carried out. Thereafter, dropping of riboflavin (Vibex Xtra) was carried out every 1.5 min for 6 min, followed by 5.20 min accelerated CXL using the pulsed mode with 45 mW/cm 3 power.
  2. Femtosecond laser parameters for the corneal tunnel are as follows: inner diameter, 5 mm; outer diameter, 5.9 mm; depth, 75% of the thinnest central corneal thickness; incision site, at the axis of K2 (the steepest) corneal meridian. Calculations of the thinnest corneal thickness, the depth, and the steepest corneal meridian were performed using the Pentacam.


The first step is marking the corneal center by asking the patient to look at the flashing light point coming from the microscope head. This is followed by marking the center of the cornea at the point of flashing light image [Figure 5]a. [Figure 5]b shows application of the suction ring. [Figure 5]c shows the central blue mark of the corneal center. [Figure 5]d shows creation of the corneal tunnel with femtosecond laser. The patency of the opening incision site of the tunnel was ensured [Figure 5]e. A spatula was passed through the nasal limb of the tunnel [Figure 5]f.
Figure 5: Combined cross-linking with femtosecond laser Keraring implantation: (a) marking the center of the cornea at the point of fl ashing light image; (b) application of the suction ring; (c) notice the central blue mark of the corneal center; (d) creation of the corneal tunnel with femtosecond laser; (e) ensuring the patency of opening incision site of the tunnel; (f) passing a spatula through the nasal limb of the tunnel.

Click here to view


[Figure 6]a shows implantation of the temporal Keraring segment. Pushing the Keraring segment toward its position [Figure 6]b, the nasal Keraring segment was implanted [Figure 6]c. The nasal Keraring segment was pushed toward its position [Figure 6]d. [Figure 6]e shows dropping of the transepithelial riboflavin onto the cornea. [Figure 6]f shows epithelium-on CXL using accelerated pulsed mode.
Figure 6: Combined cross-linking with femtosecond laser Keraring implantation: (a) implantation the temporal Keraring segment; (b) pushing the Keraring segment toward its position; (c) implantation of the nasal Keraring segment; (d) pushing the nasal Keraring segment toward its position, (e) dropping of the transepithelial ribofl avin onto the cornea; (f) epithelium-on CXL using accelerated pulsed mode.

Click here to view



  Results Top


Forty-six eyes of 30 patients (18 male and 12 female) were included in the study, and the male-to-female ratio was 3 : 2. The mean age was 18.45 ± 6.70 years. The preoperative data of patients and the postoperative data at the sixth postoperative month for both groups are summarized in [Table 1] and [Table 2].
Table 1: The preoperative and postoperative data of group A eyes with combined cross-linking with femtosecond laser Myoring implantation

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Table 2: The preoperative and postoperative data of group B eyes with combined cross-linking with femtosecond laser Keraring implantation

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As regards postoperative visual acuity in group A, the UCVA and BCVA showed excellent improvement (two lines or more). What was amazing is the postoperative K average that showed a huge reduction in the myopic component of keratoconus, reaching up to 8 D or more (range: 4.5-10.5 D). However, the improvement in the astigmatic component of keratoconus was little and ranged from 0.50 to 2.00 D.

Thus, almost all patients in this group expressed their satisfaction and happiness with their newly gained postoperative visual acuity, as more details became clearer postoperatively.

In group B, there were different results from group A. There was an excellent improvement with regard to postoperative UCVA and BCVA (two lines or more). The K average showed a good reduction, reaching up to 3 D (range: 2-4 D) or more in some cases.

What took the attention most was the excellent effect of Keraring in reducing the mean preoperative astigmatism from 4.32 to 0.52 D postoperatively. Postoperative astigmatic correction reached up to 4 D or more in some cases. In contrast, the mean postoperative myopic correction was 1.25 D and did not exceed 2 D in any case.

This study showed good postoperative mean UCVA. This can be explained on the basis that there was a good selection for the patients included in this study.

The difference between the two groups is shown in [Table 3] and [Table 4].
Table 3: Example of group A eyes: the preoperative and postoperative data of the right eye of one patient with combined cross-linking and femtosecond laser Myoring implantation

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Table 4: Example of group B eyes: the preoperative and postoperative data of the right eye of one patient with combined cross-linking and femtosecond laser Keraring implantation

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Furthermore, the clinical comparison between the two procedures is shown in [Table 5].
Table 5: The clinical comparison between combined cross-linking with femtosecond laser Myoring implantation and combined cross-linking with femtosecond laser Keraring implantation

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  Discussion Top


Forty-six eyes of 30 patients (18 male and 12 female) were included in the study, and the male-to-female ratio was 3 : 2. The mean age was 18.45 ± 6.70 years.

In all studied eyes, the preoperative and postoperative mean UCVA and BCVA increased two lines or more. In group A the mean postoperative myopic correction was 8.24 D, whereas the mean postoperative astigmatic correction was 1.51 D. This points to the great success of the combined CXL with Myoring implantation in effectively reducing the myopic component of keratoconus with limited effect on the astigmatic component of keratoconus. The Myoring succeeded in flattening all meridians of the cornea nearly symmetrically, which explains its high success in correcting the myopic component of keratoconus more compared with the astigmatic components.

Meanwhile, in group B the mean postoperative myopic correction was 1.45 D, whereas the mean postoperative astigmatic correction was 3.07 D. This points to the great success of the combined CXL with Keraring implantation in effectively reducing the astigmatic component of keratoconus with limited effect on the myopic component of keratoconus. This study showed that Keraring succeeded in flattening the steeper corneal meridians with little influence on the flatter corneal meridians, which explains why Keraring corrects mainly the astigmatic component.

What was strongly noted in this study is simply that there were no signs of postoperative deterioration of any case included in this study. This can be explained on the basis that CXL is the only surgical procedure that can hold the progression of keratoconus. Furthermore, the significant postoperative visual improvement is attributed to the mechanical action of the implanted rings.

Furthermore, there was an important issue that was noticed in this study, which was the use of two different CXL techniques in both groups. Pocket CXL was used with Myoring implantation, whereas epithelium-on CXL was used with Keraring implantation. However, this study compared the combined procedures and may be the technique of CXL used in each group had an extra effect that could not be noted in this study.

Daxer [5] reported that there was no significant difference in the results between Myoring treatment of central and noncentral cones. In contrast, this study revealed that Myoring was best in cases with central or nipple cones.

Furthermore, Daxer [5] showed that in the central cone the corrective power of Myoring acts mainly concentric around the optical axis with a central flattening effect of 10 D. There were close similarities in the results between this study and the study by Daxer, as this study revealed that Myoring reduced the myopic component of Keratoconus up to 10.50 D when used to correct the central cone.

In their study, Daxer et al. [2] and colleagues raised the question whether keratoplasty can be replaced by intracorneal implants in combination with corneal CXL in the future treatment of keratoconus. Such a replacement may significantly reduce the rate of complications as well as the period of discomfort and recovery time for the patient. The CISIS provides a new option for keratoconus management. The technique appears to be safe and effective in decreasing myopia, corneal steepness, and decentration of the corneal apex, and is also potentially reversible. In addition, CISIS can be combined with CXL [2].

Similar results were reported by Jabbarvand et al. [6], who showed that Myoring ICR implantation in keratoconus appears to be an acceptable substitute for keratoplasty in advanced keratoconus. Both studies used femtosecond laser for creation of the intrastromal corneal pocket for Myoring implantation. Furthermore, Daxer et al. [7] reported that treatment of keratoconus with Myoring intracorneal continuous ring implantation significantly improved visual function.

This study proved that combined CXL with Keraring implantation had the best results in cases with oblique or oval cones. In addition, this procedure succeeded in reducing the astigmatic component of keratoconus 4 D or more. Furthermore, this study showed that most of the improvements in keratometry results were in the steep corneal meridians (K2 or Kmax ), with little influence on the flat corneal meridians.

Supporting the results of this study, Gharaibeh et al. [8] reported that Keraring implantation provided a significant improvement in visual acuity, spherical equivalent, and keratometry results. It is an effective treatment for managing keratoconus and might delay or even avoid the need for penetrating keratoplasty.

In this study, advanced femtosecond laser (iFS; Abbott) was used with no recorded intraoperative complications. Similar results were reported by Coimbra et al. [9], who showed that intrastromal corneal ring implantation with the use of a femtosecond laser was a safe procedure, with low risk for complications and significant improvement on visual acuity and topographic data in this setting of patients with secondary corneal ectasia.

This study results were similar to those of Hosny et al. [10], who reported that both complete ring and ring segment implantation are effective for improving corneal and visual parameters in keratoconus. Complete ring implantation may have a greater flattening effect on the anterior corneal surface [10].

Furthermore, they reported that implantation of Myorings and Kerarings by means of femtosecond technology in cases of keratoconus significantly reduced the myopic spherical error due to central corneal flattening. The CISIS provides a new option for keratoconus management. The technique appears to be effective for decreasing myopia, corneal steepness, and decentration of the corneal apex, and it is also potentially reversible. In addition, corneal intrastromal rings can be combined with corneal CXL. Complete ring implantation may have a more flattening effect on the anterior corneal surface [10].

This study proved that there is a synergistic action when CXL is combined with ICRs (Myoring of Keraring). This can be explained by the fact that both procedures have different types of actions on the keratoconic cornea. At a time when CXL succeeded to halt the progression of the keratoconus and to flatten the cornea, the ICRS succeeded to add more corneal flattening, thus giving the augmented synergistic action by reducing both myopic and astigmatic components of the keratoconus.

Similar results were reported by El-Raggal [11], who stated that combined Keraring insertion and CXL can be performed safely in one or two sessions. However, the same-session procedure appears to be more effective with regard to the improvement in the corneal shape [11]. Furthermore, in another study, El-Raggal [12] reported that femtosecond laser channel creation can be performed after CXL; however, the laser power must be modified. The results show that channel dissection and ICRS implantation should be performed before or concurrent with CXL [12].


  Conclusion Top


This study proved that combined CXL with Myoring implantation is effective in the correction of the myopic component of keratoconus. Combined CXL with Keraring implantation is effective in correction of the astigmatic component in keratoconus. The type and the site of keratoconus cone together with the K readings can help in the preoperative decision of which type of both rings is best in each keratoconus case. This study proved that there is a synergistic action when CXL combined with ICRs (Myoring of Keraring).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Spoerl E, Hafezi F, Bradley J. Corneal collagen cross-linking. SLACK Incorporated 2013; 20:139-142.  Back to cited text no. 1
    
2.
Daxer A, Mahmoud H, Venkateswaran RS. Implantation of a complete corneal ring in an intrastromal pocket for keratoconus. J Refract Surg 2011; 27:63-68.  Back to cited text no. 2
    
3.
Dioptex Industries. CISIS, Pocketmaker, Myoring. Available at: http://www.dioptex.com/products/myoring-corneal-implant. [Accessed 15 April 2014]  Back to cited text no. 3
    
4.
Coskunseven E, Kymionis GD, Tsiklis NS, Atun S, Arslan E, Jankov MR, Pallikaris IG. One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. Am J Ophthalmol 2008; 145:775-779.  Back to cited text no. 4
    
5.
Daxer A. Myoring for central and noncentral keratoconus. Int J Keratoconus Ectatic Corneal Dis 2012; 2:17-119.  Back to cited text no. 5
    
6.
Jabbarvand M, Salamatrad A, Hashemian H, Mazloumi M, Khodaparast M. Continuous intracorneal ring implantation for keratoconus using a femtosecond laser. J Cataract Refract Surg 2013; 39:1081-1087.  Back to cited text no. 6
    
7.
Daxer A, Mahmoud H, Venkateswaran RS. Intracorneal continuous ring implantation for keratoconus: one-year follow-up. J Cataract Refract Surg 2010; 36:1296-1302.  Back to cited text no. 7
    
8.
Gharaibeh AM, Muhsen SM, AbuKhader IB, Ababneh OH, Abu-Ameerh MA, Albdour MD KeraRing intrastromal corneal ring segments for correction of keratoconus. Cornea 2012; 31:115-120.  Back to cited text no. 8
    
9.
Coimbra CC, Gomes MT, Campos M, Figueiroa ES Jr, Barbosa EP, Santos MS. Femtosecond assisted intrastromal corneal ring (ISCR) implantation for the treatment of corneal ectasia. Arq Bras Oftalmol 2012; 75:126-130.  Back to cited text no. 9
    
10.
Hosny M, El-Mayah E, Sidky MK, Anis M. Femtosecond laser-assisted implantation of complete versus incomplete rings for keratoconus treatment. Clin Ophthalmol 2015; 9:121-127.   Back to cited text no. 10
    
11.
El-Raggal TM. Sequential versus concurrent KERARINGS insertion and corneal collagen cross-linking for keratoconus. Br J Ophthalmol 2011; 95:37-41.  Back to cited text no. 11
    
12.
El-Raggal TM. Effect of corneal collagen crosslinking on femtosecond laser channel creation for intrastromal corneal ring segment implantation in keratoconus. J Cataract Refract Surg 2011; 37:701-705.  Back to cited text no. 12
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

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



 

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