|Year : 2015 | Volume
| Issue : 1 | Page : 5-9
Refractive meridional corneal collagen cross-linking: a new modified technique for treatment of astigmatism
Mohamed Iqbal Hafez
Department of Ophthalmology, Sohag University Hospital, Sohag, Egypt
|Date of Submission||15-Jul-2014|
|Date of Acceptance||01-Oct-2014|
|Date of Web Publication||29-May-2015|
Mohamed Iqbal Hafez
Department Of Ophthalmology, Sohag University Hospital, 82425, Sohag
Source of Support: None, Conflict of Interest: None
The aim of the study was to evaluate the efficacy and safety of using corneal collagen cross-linking as a refractive procedure to correct corneal astigmatism.
This study was conducted in Sohag University Hospital (Egypt).
This is a prospective, nonrandomized, clinical trial study.
Patients and methods
Fifteen eyes of 11 patients complaining of astigmatism were treated with refractive meridional cross-linking (RMCXL). Group A included eight eyes that had undergone previous cross-linking and implantation of intracorneal rings that failed to correct the astigmatic component of keratoconus. Group B included seven eyes with astigmatism without corneal ectasia. All eyes were subjected to examination of the preoperative and postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction, as well as slit lamp examination of the anterior segment, keratometry, and pachymetry by corneal topographies at 1 week and at 1, 3, and 6 months' follow-up.
In group A, the preoperative mean UDVA was 0.90 ± 0.33 (log MAR ± SD), whereas the postoperative mean UDVA was 0.78 ± 0.27. The preoperative mean CDVA was 0.60 ± 0.38, whereas the postoperative mean CDVA was 0.48 ± 0.26. The mean postoperative astigmatic correction was 1.8 ± 0.36. In group B, the preoperative mean UDVA was 0.78 ± 0.53, whereas the postoperative mean UDVA was 0.52 ± 0.23. The preoperative mean CDVA was 0.52 ± 0.26, whereas the postoperative mean CDVA was 0.30 ± 0.15. The mean postoperative astigmatic correction was 0.90 ± 0.29.
RMCXL showed good refractive correction for astigmatism in both ectatic and nonectatic corneas. RMCXL proved to be a promising new simple, effective, and safe procedure for the treatment of corneal astigmatism with reasonable patient satisfaction.
Keywords: astigmatism, cross-linking, keratoconus, refractive
|How to cite this article:|
Hafez MI. Refractive meridional corneal collagen cross-linking: a new modified technique for treatment of astigmatism. Delta J Ophthalmol 2015;16:5-9
|How to cite this URL:|
Hafez MI. Refractive meridional corneal collagen cross-linking: a new modified technique for treatment of astigmatism. Delta J Ophthalmol [serial online] 2015 [cited 2017 Oct 18];16:5-9. Available from: http://www.djo.eg.net/text.asp?2015/16/1/5/157776
| Introduction|| |
Corneal collagen cross-linking (CXL) is the first surgical procedure that appears to halt the progression of corneal ectatic disorders such as keratoconus and postoperative corneal ectasia after refractive surgery.CXL offers a treatment for corneal disease for which there is no option to address the underlying disorder  .
In most eyes treated with CXL, there was no remarkable improvement in the corneal astigmatism; the basic improvement was the decrease in the corneal curvature, thus decreasing the myopic element of the keratoconus  .
Kanellopoulos reported the novel application of very high-fluence collagen cross-linking with a predictable well-defined myopic refractive (flattening) corneal effect. This technique has the advantages of essentially no postoperative morbidity, immediate visual rehabilitation, and the potential for tapering until the desired result is achieved  .
Refractive meridional cross-linking (RMCXL) is a new term that was introduced by the author to describe the new modified technique for treatment of astigmatism in ectatic and nonectatic corneas.
This new technique is quite simple and is a trial to help patients with astigmatism. In a previous study by the author, the results became clear that CXL was greatly helpful in correcting the myopic component of keratoconus of up to 5 D but with little influence on astigmatism with no obvious explanation. The explanation, however, may be quite simple: CXL affects all meridians of the cornea symmetrically and thus there is no remarkable improvement in the astigmatic component of the refractive error.
RMCXL represents a novel, simple procedure of cross-linking the steep meridians to flatten them, thus correcting astigmatism either partially or totally.
| Patients and methods|| |
This study was designed as a prospective clinical trial that was performed in Sohag University Hospital after obtaining approval from the ethics committee. Written consent form was taken from the patients after explanation of the new procedure for correction of their astigmatism.
In this study, it was decided to evaluate the efficacy of RMCXL in correcting astigmatism in both ectatic and nonectatic eyes.
Fifteen eyes of 11 patients complaining of astigmatism were treated with meridional cross-linking to correct the refractive error. The principle of treatment was to expose the steep corneal meridians to cross-linking to flatten them, thus reducing astigmatism.
The study eyes were divided into two groups:
- Group A included eight eyes. All eyes in this group had undergone previous cross-linking and implantation of intracorneal rings that managed to greatly halt keratoconus progression and correct the myopic component but failed to correct the astigmatic component of the keratoconus. All eyes were subjected to RMCXL.
- Group B included seven eyes with astigmatism without corneal ectasia that were subjected to RMCXL.
All eyes were subjected to examination of the preoperative and postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction, as well as slit lamp examination of the anterior segment, evaluation of intraocular pressure, fundus examination, keratometry, and pachymetry as assessed by Pentacam corneal topographies at 1 week and at 1, 3, and 6 months' follow-up.
The conventional (epithelium-off) CXL procedure was used to treat all eyes.
The device used was first-generation Avedro (Avedro Inc. MA, USA) (KXL System). The parameters used were power 30 mW, energy 7.2 mJ/cm 3 , time 8 min, and pulsed mode [Figure 1]a.
|Figure 1: The device and material used: (a) Avedro (KXL System). (b) VibeX Rap id (0.1% ribofl avin).|
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The riboflavin used was VibeX Rapid, composed of 0.1% riboflavin, saline, and hydroxyproyl methylcellulose, with no dextran. It has a diffusion rate twice that of standard riboflavin [Figure 1]b.
All eyes were subjected to meridional epithelium-off CXL. The eye was marked and a topical anesthetic (benoxinate hydrochloride) was instilled every 10 min for 30 min. Skin disinfection was performed by prepping the skin with povidone iodine 10%.
Marking the steep meridians was the first and the most critical step in this surgical procedure [Figure 2]a. For this purpose, an ophthalmic protractor instrument was used by placing it in the 90° orientation and then marking the steep meridians with the pen marker on both sides [Figure 2]b. Thereafter, the instrument was removed and the connection between the two-dot marks represented the steep meridians [Figure 2]c.
|Figure 2: The operative procedure: (a) Marking the steep meridians with a pen marker. (b) The two-dot marks. (c) Removal of the ophthalmic protractor instrument. (d) Epithelium removal with a blunt-tipped spatula along the two-dot path. (e) Creation of the de-epithelialized corneal track. (f) The arrow points toward the implanted kera ring.|
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The second vital step was removal of the epithelium along the two-dot path with a blunt-tipped spatula [Figure 2]d. Approximately 10° of the steep meridians along their two-dot axes was involved in epithelial removal, so that the steepest meridians were in the middle of these 10°. This created an epithelium-off track along the whole corneal steep meridians, which was named the de-epithelialized corneal track [Figure 2]e. [Figure 2]f shows an arrow that points to the implanted intracorneal kera ring of one eye in group A.
The next step involved soaking of the corneal track with riboflavin [Figure 3]a. VibeX Rapid was chosen because it can only be absorbed through a de-epithelialized corneal area and thus we were assured that only the created corneal track would absorb the riboflavin and only the steep meridians could be cross-linked.
|Figure 3: Continuation of the operative procedure: (a) VibeX Rapid was instilled along the created de-epithelialized corneal track. (b) Ribofl avin was instilled every 2 min for 10 min. (c) Adjustment of Avedro (KXL System) on the eye. (d) Corneal xposure to UVA light for 8 min in pulsed mode. (e) Rat tail appearance of the deepithelialized corneal track. (f) Soft contact lens appli cation on the cornea|
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VibeX Rapid was instilled along the created de-epithelialized corneal track every 2 min for 10 min [Figure 3]b. Avedro (KXL System) was then adjusted on the patient's eye [Figure 3]c. This was followed by corneal exposure to UVA light for 8 min in a pulsed mode using the KXL System while only balanced salt saline was used to irrigate the cornea every 30 s during these 8 min [Figure 3]d.
Surprisingly enough, the de-epithelialized track was highly demarcated by the fluorescence of riboflavin under UVA light during CXL, giving what is called a green rat tail appearance [Figure 3]e.
Finally, irrigation of the cornea with balanced salt saline and soft contact lens application onto the cornea were performed [Figure 3]f.
[Figure 4] shows clearly the rat tail appearance of the de-epithelialized corneal track together with the implanted intrastromal kera rings in one eye from group A.
|Figure 4: Rat tail appearance of the de-epithelialized corneal track together with the implanted int rastromal kera rings.|
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The postoperative treatment included instillation of antibiotic eye drops (Gatifloxacin 0.3%) four times daily. Steroid eye drops (Perdnisolone acetate 1%) were used three times daily from the first postoperative day. Topical gel was used twice daily. Systemic vitamin A and vitamin C were used twice daily. The treatment usually lasted 1-2 weeks postoperatively.
Postoperatively, all patients were examined by the slit lamp to detect re-epithelialization, corneal edema, or haze. The patient was followed up at week 1 and at 1, 3, and 6 months postoperatively.
During the follow-up period, re-epithelialization was seen to usually take place in the first 2-3 days postoperatively. Delayed healing occurred only on the corneal areas above the intrastromal corneal rings in which re-epithelialization took place during the first 5-7 days. The contact lens was removed after complete re-epithelialization had occurred and the patient was advised to wear sunglasses for 1 week.
| Results|| |
Fifteen eyes of 11 patients were included in the study. The mean age was 23.66 ± 4.70 years with an overall male to female ratio of 3:2. The preoperative data of patients and the postoperative data at the sixth postoperative month are summarized in [Table 1] and [Table 2].
|Table 1: Summary of the preoperative and postoperative data of group A eyes|
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|Table 2: Summary of the preoperative and postoperative data of group B eyes|
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In group A, there was remarkable improvement in postoperative UDVA and CDVA (one line or more). The preoperative mean UDVA was 0.90 ± 0.33 (log MAR ± SD), whereas the postoperative mean UDVA was 0.78 ± 0.27. The preoperative mean CDVA was 0.60 ± 0.38, whereas the postoperative mean CDVA was 0.48 ± 0.26.
Furthermore, the mean K average showed a marked reduction reaching up to 2 D in some cases. The preoperative mean K average was 49.27 ± 1.77, whereas the postoperative mean K average was 48.04 ± 1.46. The mean postoperative astigmatic correction was 1.8 ± 0.36.
Surprisingly enough, most of the reduction in the postoperative mean K average was in the steep meridians that showed considerable reduction in the refractive power that ranged from 1 to 2.5 D. These results proved the success of RMCXL in flattening the steep corneal meridians. Further, RMCXL proved to be effective in visual stabilization and improvement. In contrast, the flat corneal meridians showed no remarkable changes in the postoperative K readings.
In addition, the preoperative mean central corneal thickness was 427 ± 15.75 μm, which showed a noticeable reduction postoperatively to 412 ± 14.88 μm.
Group B showed similar results as group A. Both postoperative UDVA and CDVA showed good improvement (one line or more). The preoperative mean UDVA was 0.78 ± 0.53, whereas the postoperative mean UDVA was 0.52 ± 0.23. The preoperative mean CDVA was 0.52 ± 0.26, whereas the postoperative mean CDVA was 0.30 ± 0.15.
The postoperative mean K average showed a considerable reduction reaching up to 1 D. Also, most of the main reduction in postoperative mean K average took place in the steep meridians that became flatter with reduction in their refractive power that ranged from 0.5 to 1.5 D. The preoperative mean K average was 43.72 ± 1.80, whereas the postoperative mean K average was 42.55 ± 1.42. The mean postoperative astigmatic correction was 0.90 ± 0.29.
Furthermore, the preoperative mean central corneal thickness was 510 ± 20.37 μm, which showed a little reduction postoperatively to 502±9.39 μm.
What is amazing in this study is that we managed to achieve postoperative astigmatic reduction in spectacle correction that reached up to 1.8 D in group A and 0.9 D in group B. As a result, many patients were satisfied with their new spectacle prescription as fine details could be clearly visualized with the new glasses.
To appreciate the difference in the results between the two groups, the preoperative and postoperative data of both groups are 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 keratoconus|
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|Table 4: Example of group B eyes: the preoperative and postoperative data of the right eye of one patient with pseudophakia|
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| Discussion|| |
The main principle behind RMCXL is the use of CXL as a refractive tool that induces corneal flattening. The flattening effect of CXL can be beneficial in reducing the refractive power of certain corneal areas according to the corneal topography pattern, which is called topography-guided CXL, a novel technique of the new Avedro KXL II device, which is still under experimental studies and not available in the market yet.
However, the simple idea behind RMCXL is ensuring that only the steep corneal meridians are cross-linked. This was achieved in this study by the novel method of creating the de-epithelialized corneal track with the use of only epithelium-off riboflavin. This ensured that only the steep corneal meridians stroma absorbed the riboflavin while the remaining cornea did not absorb any riboflavin and was not affected by CXL.
Piñero et al.  reported that cross-linking induces a corneal astigmatic change, but it is variable, not predictable, and insufficient to provide effective astigmatic correction. Similar results were reported by Iqbal  who stated that most of the post-cross-linking visual improvement resulted from decrease of myopia and that there was no remarkable improvement in astigmatism as the conventional CXL affects all meridians of the cornea symmetrically. This formed the foundation for the creation of RMCXL.
In this study, Avedro KXL was used with 7.2 mJ/cm 3 energy with pulsed mode. Fifteen eyes of 11 patients complaining of astigmatism, with or without ectasia, were treated with RMCXL. In all eyes, the postoperative UDVA and CDVA improved by one or more lines. The postoperative astigmatic reduction ranged from 0.50 to 2.50 D cylinder with a mean postoperative astigmatic correction of up to 1.8 ± 0.36 in group A and 0.90 ± 0.29 in group B.
Kanellopoulos  used the high-fluence CXL intervention and succeeded in the correction of 2 D of topographic and refractive cylinder in his case report. UDVA changed from 20/50 to 20/20 and refraction from −0.50 to −2.00 at 90 to +0.25 to −0.25 at 90 at the 7-month follow-up. He concluded that this could be a possible novel application of high-fluence CXL with refractive cornea effect, offering rapid and simple rehabilitation, with a tapering of its effect.
Moreover, Kanellopoulos  reported the results of four cases that were treated with a novel device using very high-fluence collagen cross-linking applied in a myopic pattern. An average of 2.3 D was achieved in the first week in all four cases treated with the very high-fluence myopic collagen cross-linking intervention.
| Conclusion|| |
Refractive meridional corneal collagen cross-linking (RMCXL) showed good refractive correction for astigmatism in both ectatic and nonectatic corneas. RMCXL proved to be a promising new simple, effective, and safe procedure for the treatment of corneal astigmatism with reasonable patient satisfaction. However, long-term studies are necessary to prove the efficacy and safety of RMCXL.
| Acknowledgements|| |
Conflicts of interest
| References|| |
Doyle R, Waring J, Santhiago M. Patient selection for corneal collagen cross-linking. In: Hafezi F, Bradley J. Corneal collagen cross-linking
. Geneva, Switzerland: SLACK Incorporated 2013; 5:41-44.
Iqbal M. Analysis of two-year corneal cross-linking results in keratoconus patients. Delta J Ophthalmol 2013; 2:113-120.
Kanellopoulos AJ. Novel myopic refractive correction with transepithelial very high-fluence collagen cross-linking applied in a customized pattern: early clinical results of a feasibility study. Clin Ophthalmol 2014; 8:697-702.
Piñero DP, Alio JL, Klonowski P, Toffaha B Vectorial astigmatic changes after corneal collagen crosslinking in keratoconic corneas previously treated with intracorneal ring segments: a preliminary study. Eur J Ophthalmol 2012; Suppl 7:S69-S80.
Kanellopoulos AJ. Very high fluence collagen cross-linking as a refractive enhancement of a regressed previous astigmatic keratotomy. J Refract Surg 2013; 29:504-505.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]