Delta Journal of Ophthalmology

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 19  |  Issue : 3  |  Page : 178--190

Myoring and Ferrara ring segment implantation using femtosecond laser for treatment of keratoconus


Mohamed I EL-Kasaby 
 Department of Ophthalmology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Correspondence Address:
Mohamed I EL-Kasaby
Department of Ophthalmology, Faculty of Medicine, Al-Azhar University, Assist prof of Ophthalmology Cairo, Egypt; 93 AL-Mahdy Bin Baraka Street, Seventh Avenue, Nasr City 11816
Egypt

Abstract

Purpose To compare visual acuity, refraction, and topographic corneal changes after implantation of a MyoRing versus Ferrara ring segment for management of keratoconus. Patients and methods This is a prospective nonrandomized clinical comparative study. Forty eyes of 25 patients with keratoconus grades 2–4 were included in the study and were divided into two groups: group A (MyoRing group) included 20 eyes of patients with keratoconus subjected to femtosecond laser-assisted MyoRing implantation and group B included 20 eyes of patients with keratoconus subjected to femtosecond laser-assisted Ferrara ring segment implantation. Results Forty eyes of 25 patients (12 males and 13 females) with keratoconus grades 2–4 were enrolled in this study. The mean age of the patients in group A was 26.62±6.18 years and in group B was 24.72±5.06 years. The mean central corneal thickness improved from 440.25 to 476.57 µm in group A and from 441.35 to 470.63 μm in group B. The mean keratometric (K) reading decreased from 49.97±14.26 to 44.55±2.16 D in group A and from 48.69+4.26 to 44.85±1.92 D in group B. There was a statistically significant improvement in the postoperative uncorrected distance visual acuity, corrected distance visual acuity, K readings, manifest spherical and cylindrical refractive errors, and spherical equivalent in both groups. No serious intraoperative complications were reported. Conclusion Both MyoRing and Ferrara ring segments are effective modalities for treatment of grades 2–4 keratoconus, but MyoRing had a superior capability in improving the keratoconus parameters as well as in halting the progression of the disease.



How to cite this article:
EL-Kasaby MI. Myoring and Ferrara ring segment implantation using femtosecond laser for treatment of keratoconus.Delta J Ophthalmol 2018;19:178-190


How to cite this URL:
EL-Kasaby MI. Myoring and Ferrara ring segment implantation using femtosecond laser for treatment of keratoconus. Delta J Ophthalmol [serial online] 2018 [cited 2018 Oct 18 ];19:178-190
Available from: http://www.djo.eg.net/text.asp?2018/19/3/178/242152


Full Text



 Introduction



Keratoconus is a bilateral progressive, noninflammatory ectatic corneal disease characterized by changes in corneal collagen structure and organization. Though the etiology remains unknown, novel techniques are continuously emerging for the diagnosis and management of the disease. Intracorneal ring segment (ICRS) implantation can improve vision by flattening the cornea in patients with mild to moderate degree of keratoconus [1].

The recently proposed MyoRing is a complete intrastromal ring designed to be placed into a corneal pocket. A potential advantage of the MyoRing over other corneal ring segments (CRSs) is its effectiveness in advanced keratoconus with a higher reduction of the keratometric (K) power [2]. Alio et al. [3] reported in a pilot study that femtosecond laser-assisted MyoRing implantation had satisfactory 6-month results regarding vision, refraction, corneal keratometry, and corneal biomechanical properties.

The aim of this study was to compare visual acuity, refraction, and topographic corneal changes after MyoRing versus Ferrara ring segment implantation for management of keratoconus.

 Patients and methods



Forty eyes of 25 patients with keratoconus grades 2–4 were enrolled in this nonrandomized prospective study. This study was conducted in Nour EL-Hayaha Eye Center (Cairo) between June 2015 and July 2017. Patients with a history of previous ocular surgery and coexisting ocular diseases other than keratoconus were excluded. Patients who failed to complete follow-up examinations 1 month after surgery were also excluded.

The demographic data, material, and position of intracorneal ring, and ocular examination results, including measurements of uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (BDVA), using automated chart projector (ACP.8; Topcon Corporation, Tokyo, Japan), and converted to the logarithm of the minimum angle of resolution (logMAR), were recorded. The refractive status was assessed using an auto refractometer (KR-8100; Topcon Corporation). Intraocular pressure was measured by Goldman applanation tonometry (CT-80; Topcon Corporation). Slit lamp examination and fundus evaluation were done by using an indirect ophthalmoscope.

Corneal indices were evaluated using the Pentacam (Oculus Pentacam; Optikgerate GmbH, Wetzlar, Germany).

Inclusion criteria included age between 18 and 35 years, maximum K reading less than 60 D (based on Pentacam examination), and a central corneal thickness (CCT) of at least 370 µm. Patients who had corneal scarring, any concomitant ocular disease, or any history of ocular surgery were excluded from the study. Patients who failed to complete follow-up examinations 1 month after the surgery were also excluded.

Patients were classified into two groups:Group A: eyes of this group were subjected to a continuous (360°) intrastromal 6-mm MyoRing (Dioptex GmbH, Linz, Austria) implantation.Group B: eyes of this group were subjected to Ferrara ring segment (Mediphacos Inc., Belo Horizonte, Brazil) implantation.

A written informed consent was signed by all patients. The study was approved by the Ethical Committee of the Faculty of Medicine, Al-Azhar University.

Surgical technique

In group A, topical antibiotics were prescribed 2 days before surgery. After topical anesthesia (0.5% propacaine hydrochloride eye drops), the pupil center was marked with a Sinskey hook. This mark was used as a reference point to locate the incision and to center the ring during implantation. A temporal upper corneal incision of 90° of arc length was made. Afterward, an intrastromal pocket was created using the femtosecond laser (Victus Femtosecond Laser SW, version 3.2; Technolas Perfect Vision GmbH, Munich, Germany) at a depth of 80% of the corneal thickness. An 8.0-mm pocket diameter was formed (frequency 80 KHz, energy 0.95 μJ, spot spacing and line spacing of 5.2 μm). Once the pocket was created, a continuous 360° intrastromal ring, MyoRing, with a diameter of 6 mm and thickness of 350 µm was implanted.

In group B, a tunnel for Ferrara ring implantation was created at a depth of 80% of the corneal thickness with the aid of the femtosecond laser. After clearance of gas bubbles, a spatula was passed gently, and the intracorneal Ferrara ring segment was then implanted under full aseptic conditions using a special forceps, and was placed in the final position using a Sinskey hook. Topical antibiotics and a contact lens were applied.

After the procedure in both groups, topical antibiotics (for 1 week) and lubricant eye drops (for 2 months) were prescribed, and no corticosteroids were prescribed at all.

Follow-up visits were scheduled at 1 day, 1 week, and 1, 3, 6, and 18 months after surgery. During follow-up visits, patients were subjected to UDVA and BDVA assessment, slit lamp examination, and fundus examination. Anterior segment OCT (Heidelberg Engineering Inc., Franklin, Massachusetts, USA) was used postoperatively to determine the tunnel depth for the implant.

Pentacam examination was repeated at 1, 3, 6, and 18 months postoperatively.

Statistical analysis

The sample size was calculated according to Raosoft, and all statistical calculations were done using statistical package for the social science (version 20.00; SPSS Inc., Chicago, Illinois, USA). Quantitative data with parametric distribution were assessed using analysis of variance t test. The confidence interval was set to 95%, and the margin of error accepted was set to 5%. The P value was considered nonsignificant at the level of more than 0.05, significant at the level of less than 0.05 and 0.01, and highly significant at the level of less than 0.001. Pearson’s linear correlation coefficient (r) was estimated to show the relationship between quantitative parameters [4].

 Results



Forty eyes of 25 patients (12 males; 48% and 13 females; 52%) with keratoconus grades 2–4 were enrolled in this study ([Table 1]). Group A included 20 eyes of 12 patients [six (50%) males and six (50%) females]. Group B included 20 eyes of 13 patients [six (46.15%) males and seven (53.85%) females]. The mean age of both groups was 25.67±5.14 years (range, 18–35 years). In group A, the mean age of the participants was 26.62±6.18 years (range, 20–35 years), whereas in group B, the mean age of the participants was 24.72±5.06 years (range, 18–34 years). Statistically, the differences between both groups regarding age and sex were insignificant.{Table 1}

All patients completed the regular follow-up visits up to 18 months.

Overall, 22 (55%) eyes had keratoconus grade 2, 14 (35%) eyes had keratoconus grade 3, and four (10%) eyes had keratoconus grade 4. In group A, 12 (60%) eyes had keratoconus grade 2, six (30%) eyes had keratoconus grade 3, and two (10%) eyes had keratoconus grade 4. In group B, 10 (50%) eyes had keratoconus grade 2, eight (40%) eyes had keratoconus grade 3, and two (10%) eyes had keratoconus grade 4 ([Table 1]). In MyoRing group, the mean horizontal radius of curvature (rh) was 7.01±0.79 D, the mean vertical radius of curvature (rv) was 6.53±0.68 D, and the mean radius of curvature (rm) was 6.77±0.71 D, which improved postoperatively to 7.90±0.59, 7.45±0.57, and 7.68±0.51 D, respectively (P<0.000, [Figure 1],[Figure 2],[Figure 3]). In group B, the mean rh was 7.02±0.63 D, mean rv was 6.81±0.64 D, and the mean rm was 7.92±0.59 D, which improved postoperatively to 7.88±0.32, 7.51±0.56, and 7.69±0.46, respectively (P<0.003, [Figure 4] and [Figure 5], [Table 2]).{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Table 2}

In group A ([Table 4]), the mean k1 was 47.37±4.64 D, with axis 52.02±5.32, and the mean k2 was 52.57±5.24 D, with axis 97.31±29.33. The mean K reading preoperatively was 49.97±4.26 D, with axis 74.66±29.79. At the end of follow-up visits (at 18 months postoperatively), the mean k1 reading improved to 43.32±3.14 D (P<0.000) with axis 38.93±9.79 (P<0.383), and the mean k2 improved to 45.77±2.16 D (P<0.000) with axis 121.30±23.62 (P<0.000) ([Figure 6]). In group B, the mean k1 was 47.06±2.59 D with axis 145.00±36.20, and the mean k2 was 50.33±3.61 D with axis 88.19±21.22. The mean K reading was 48.69±4.26 D with axis 75.91±116.59. At the end of follow-up visits (at 18 months postoperatively), the mean k1 readings improved to 44.04±2.92 D (P<0.001) with axis 34.64±15.88 (P<0.3) and k2 improved to 45.65±1.9 D (P<0.000) with axis 135.30±45.3 (P<0.000) ([Figure 6] and [Figure 7], [Table 3]).{Table 3}{Table 4}{Figure 6}{Figure 7}

In group A, the mean astigmatic error improved from −5.2 D preoperatively to −2.45 D at the end of the follow-up period, whereas in group B, the mean astigmatic error improved from −3.27 D preoperatively to −1.61 D at the end of the follow-up period.

In group A, the mean corneal eccentricity preoperatively was −2.23±0.84 mm. It was changed postoperatively to −1.17±0.35 mm (P<0.396). The mean CCT was 440.25±44.49 µm preoperatively, and it improved to 476.57±41.36 µm postoperatively (P<0.011). The thinnest corneal location preoperatively was 421.50±44.28 µm. It improved to 452.20±37.50 µm postoperatively (P<0.023). In group B, the mean corneal eccentricity preoperatively was −0.78±0.28 mm. It was changed postoperatively to −0.44±0.31 mm (P<0.219). The mean CCT preoperatively was 441.35±43.02 µm. It improved to 470.63±41.96 µm postoperatively (P<0.036). The thinnest corneal location preoperatively was 433.50±40.91 µm. It improved to 454.20±41.28 µm postoperatively (P<0.023).

The mean preoperative and postoperative Q values, in group A, are reported in [Table 4], with a statistically significant differences before and after surgery (P<0.001). The preoperative and postoperative data regarding CCT, thinnest corneal location, anterior chamber (AC) depth, angle of AC, pupil diameter, ART max, front elevation, and back elevation of both groups are illustrated in [Table 4] and [Table 5].{Table 5}

The mean refraction preoperatively in A group ([Figure 8],[Figure 9],[Figure 10],[Figure 11],[Figure 12]) was −4.87±3.06 D (sphere) and −6.25±2.18 D (cylinder) with axis 77.80±45.77. It improved postoperatively to −0.44±1.64 D (sphere) and −1.75±0.94 D (cylinder) with axis 90.95±26.99 (P<0.000, <0.000, and <0.036, respectively). The mean refraction preoperatively in group B was −3.40±2.48 D (sphere) and −4.02±2.42 D (cylinder) with axis 122.50±32.83. It improved postoperatively to −0.51±1.84 D (sphere) and −1.81±1.03 D (cylinder) with axis 112.00±17.50 (P<0.002, <0.017, and <0.031, respectively).{Figure 8}{Figure 9}{Figure 10}{Figure 11}{Figure 12}

In group A, the mean uncorrected visual acuity improved from 0.06±0.11 to 0.31±0.11 (P<0.000), whereas the mean best-corrected visual acuity improved from 0.11±0.09 to 0.44±0.11 (P<0.000). In group B, the mean UDVA improved from 0.05±0.13 to 0.24±0.10 (P<0.001), whereas the mean BDVA improved from 0.13±0.11 to 0.31±0.9 (P<0.000).

In group B, one (5%) case showed no improvement in keratoconus parameters ([Figure 13]); two (10%) cases showed progression in keratoconus parameters during the follow-up period and needed corneal collagen cross-linking, which was done 14 months after Ferrara ring segment implantation; and two (10%) cases showed extrusion after blunt trauma 6 weeks and 10 months after Ferrara ring segment implantation. No complications were reported in group A.{Figure 13}

 Discussion



The results of the present study showed a significant improvement in K readings, spherical errors, cylindrical errors, UDVA as well as BDVA after both MyoRing and Ferrara ring segment implantation in keratoconus early at the first follow-up visits and continued to be maximally manifested ∼3 months after surgery.

The present study showed that femtosecond-assisted intracorneal MyoRing implantation improved visual acuity and refraction, and decreased K readings after the procedure in patients with different grades of keratoconus. The results showed a significant improvement of K readings, spherical errors, cylindrical errors as well as UDVA and BDVA. The safety, efficacy, and predictability of the procedure were acceptable and in line with other studies. In group A, k1 and k2 were improved. This correlates with the 18-month study done by Mohebbi and colleagues on 47 eyes with keratoconus. They reported preoperative mean Kmax 53.57±3.72 D, which was changed postoperatively to 46.20±4.34 D at the third month and 47.08±3.84 D at the sixth month [5]. Moreover, it is consistent with a study done by Al-Tuwairqi et al. [6], who investigated 18 eyes with femtosecond laser-assisted MyoRing implantation with mean preoperative Kmax 51.46±4.38 D, which was changed postoperatively to 45.10±3.37 D at the third month and to 43.71±1.57 D at the sixth month.

The mean preoperative Q value in group A was improved postoperatively with statistically significant difference between preoperative and postoperative Q value. This finding is in accordance with a study done by Torquetti and Ferrara, who reported that ICRS implantation significantly reduced the mean corneal asphericity from −0.85 to −0.32 (P=0.000) [7],[8]. A study performed by Alio and colleagues reported that an increase of mean CCT of ∼11.5 µm was observed in the CCT 6 months after the operation. Differences could be attributed to the difference in the thickness of the rings that were used, the difference in the severity of keratoconus, variability of Pentacam CCT measurement, or the difference in the follow-up period [3]. In the current study, AC depth showed a significant decrease which may be secondary to the flattening of the anterior surface and/or the increase in the corneal thickness following the MyoRing implantation. This study disagrees with a study reported by Mohebbi et al. [5], but agrees with a study reported by Alio et al. [3]. In the present study, the mean preoperative spherical error showed a highly statistically significant difference at the follow-up periods postoperatively. This agrees with a study published by Hosny et al. [9] who investigated 15 femtosecond-assisted MyoRing implantation with improvement in spherical error postoperatively. In the present study, the mean preoperative UCVA and BCVA increased three lines or more postoperatively. MyoRing implantation is highly effective in reducing both myopic and astigmatic errors [9]. Jabbarvand and colleagues in a study done on 98 keratoconic eyes had little improvement, where the mean preoperative spherical error was −5.48±4.30 D. Postoperatively, the mean improvement in spherical error was 0.08±2.81 D at the first month, 0.08±2.90 D at the third month, 0.10±2.90 D at the sixth month, and 0.09±2.91 D at the 12th month [2]. This is in agreement with a study done by Alio et al. [3], who evaluated the cylindrical error after implantation of the MyoRing on 12 eyes by means of femtosecond laser technology. They reported a highly statistically significant improvement of cylindrical error. In the present study, the mean BCVA improved significantly at the first, third, sixth, and at 18th months postoperatively.

In group B, the Ferrara ring segment was effective in flattening the steeper meridians with a little influence on the flatter corneal meridians. Gharaieh and colleagues reported that Ferrara ring segment implantation provided a significant improvement in visual acuity, spherical equivalent, and keratometry results. They concluded that it is an effective treatment modality for keratoconus and may delay or even avoid the need for keratoplasty [10]. This study results were similar to those of Hosny and colleagues, who reported that both complete ring and ring segment implantations are effective for improving corneal and visual parameters in patients with keratoconus. They also reported that complete ring is superior over ring segment implantation regarding the anterior corneal surface [9].

In the current study, the mean preoperative spherical error showed highly statistically significant differences along the follow-up periods. Ancèle et al. [11] studied the effect of Ferrara ring implantation on 25 eyes with keratoconus. They reported a mean preoperative spherical error of −4.39±5.18 D, which significantly decreased to −1.83±3.16 D at the sixth month postoperatively. In the present study, the mean preoperative cylindrical error decreased postoperatively with statistically significant differences along the follow-up periods. Kwitko and Severo in a retrospective study with a mean follow-up period of 13.0 months assessed the outcome of Ferrara ICRS implantation on 51 keratoconus eyes. They reported that the mean preoperative cylindrical error was −3.82±2.13 D, which dropped postoperatively to −2.16±2.07 D [12]. Ancèle et al. [11] and Hamdi [13] reported that the mean preoperative cylindrical error improved significantly at the sixth month postoperatively. Unlike the refractive results, the improvement in UDVA and BDVA at the 18-month follow-up was greater in our study as compared with other studies.

In this study, the anterior segment OCT showed that the mean achieved depth of implanted rings matches with the planned depth. In 2013, Pérez-Merino et al. reported that the planned CRS depth was higher by 15–20 µm than the achieved depth, and they showed a small tilt of the intracorneal ring between 7 and 90 days postoperatively [14]. There was a statistically significant reduction of mean spherical and mean cylindrical readings throughout the follow-up period between the two groups, being more in group A.

In group A, postoperative complications were nil, whereas in group B, two cases developed extrusion after blunt trauma, two cases showed keratoconus progression that required corneal collagen cross-linking, and one case showed no improvement in keratoconus parameters after Ferrara ring segment implantation.

 Conclusion



Both MyoRing and Ferrara ring segments are effective modalities for treatment of grades 2 to 4 keratoconus, but MyoRing had a superior capability in improving the keratoconus parameters as well as in halting the progression of the disease.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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