ORIGINAL ARTICLE


https://doi.org/10.5005/jp-journals-10025-1198
International Journal of Keratoconus and Ectatic Corneal Diseases
Volume 10 | Issue 1-2 | Year 2023

Variable Thickness Intracorneal Ring Segment for the Treatment of Keratoconus


Adel Barbara1, Joseph Pikkel2, Jorge L Alio3, Ramez Barbera4, Michael Mimouni5

1,4Department of Ophthalmology, IVISION Cornea and Refractive Surgery Center, Haifa, Israel

2Department of Ophthalmology, Faculty of Health Sciences, Samson Assuta Ashdod Hospital, Ben–Gurion University of the Negev, Beersheba, Israel

3Department of Ophthalmology, Development and Innovation, VISSUM Instituto Oftalmológico, Alicante, Spain; Division of Ophthalmology, Universidad Miguel Hernández, Alicante, Spain

5Department of Ophthalmology, Rambam Health Care Campus, Bruce and Ruth Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa, Israel

Corresponding Author: Michael Mimouni, Department of Ophthalmology, Rambam Health Care Campus, Bruce and Ruth Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa, Israel, Phone: +972-52-329-2429, e-mail: michael@intername.co.il

How to cite this article: Barbara A, Pikkel J, Alio JL, et al. Variable Thickness Intracorneal Ring Segment for the Treatment of Keratoconus. Int J Kerat Ect Cor Dis 2023;10(1–2):8–12.

Source of support: Nil

Conflict of interest: Dr Adel Barbara is associated as Editor-in-Chief of this journal and this manuscript was subjected to this journal’s standard review procedures, with this peer review handled independently of the Editor-in-Chief and his research group.

Received on: 05 February 2024; Accepted on: 25 February 2024; Published on: 23 April 2024

ABSTRACT

Aim: To report outcomes of a new variable thickness intracorneal ring segment (VT-ICRS) for the treatment of keratoconus.

Methods: This was a retrospective interventional case series of consecutive keratoconus eyes that underwent VT-ICRS implantation from January 2018 to December 2020 with a minimum follow-up time of 3 months. Primary outcomes included best spectacle-corrected visual acuity (BSCVA), uncorrected distance visual acuity (UCVA) and adverse events. Secondary outcomes included keratometry and manifest refraction.

Results: Overall, 9 eyes of 7 patients with a mean age of 30.22 ± 8.58 (range, 21–49 years) of which 85.7% (n = 6) were of male gender were included. The mean follow-up time was 9.0 ± 5.3 (range, 4–17) months. No intraoperative or postoperative adverse events were identified during the follow-up period of these patients. At final follow-up, there was significant improvement in logMAR UCVA (from 0.95 ± 0.21 to 0.34 ± 0.31, p < 0.001), manifest sphere (from 1.11 ± 1.69 to −0.13 ± 0.35 D, p = 0.05), manifest cylinder (from −6.61 ± 2.83 to −2.44 ± 2.26 D, p < 0.001), K2 (51.94 ± 5.43 to 49.20 ± 5.78 D, p = 0.01), and logMAR BSCVA (from 0.35 ± 0.10 to 0.15 ± 0.14, p = 0.002). The mean safety index was 1.68 ± 0.53 (range, 1–2.50) and the mean efficacy index was 1.24 ± 0.69 (range, 0.39–2.25). Alpins refractive vector analysis revealed a mean surgically induced astigmatism (SIA) of 4.99 ± 1.20 D (range, 3.79–7.12 D) with a mean SIA axis of 96.3 ± 42.5° (range, 25.1–142°).

Conclusion: The initial results of VT-ICRS for the treatment of keratoconus are encouraging. Future studies should compare VT-ICRS to classic ICRSs for the treatment of keratoconus.

Keywords: Intracorneal, Keratoconus, Ring, Segment, Thickness, Variable.

INTRODUCTION

Keratoconus is an asymmetrical, progressive bilateral corneal disease that causes thinning and irregular steepening of the cornea.1 The progressive steepening and thinning of the cornea, if left untreated, leads to irregular astigmatism and decreased visual acuity.2 Despite advancements in therapies for preventing progression such as corneal crosslinking (CXL), patients may present with significantly impaired best-spectacle corrected visual acuity (BSCVA).

There are several treatment modalities available for keratoconus. Originally developed for the treatment of myopia, Colin et al. introduced the use of intracorneal ring segments (ICRSs) implantation for the management of keratoconus.3 Since then, ICRS implantation has been reported to improve BSCVA and irregular astigmatism,4 particularly in patients presenting with low BSCVA.46 Several advancements have been made in nomograms and types of segments to further improve outcomes.7 Recently, corneal allogenic intrastromal ring segments (CAIRS) has been reported to be a safe and effective treatment option obtaining similar results using human cornea tissue.8

More recently, several asymmetric and variable thickness ICRS (VT-ICRS) models have been reported to be effective for a more customized treatment of keratoconus.912 The purpose of the current study was to report preliminary outcomes of a new VT-ICRS for the treatment of keratoconus.

METHODS

This study was conducted in compliance with the tenets of the Declaration of Helsinki and received Research Ethics Board approval from the Assuta Ashdod Hospital ethics committee (#0181-21-AAA).

Study Participants

This is a retrospective study conducted by means of a chart review of consecutive keratoconus eyes with an Amsler–Krumeich grade II or III that underwent variable thickness intracorneal ring segment (VT-ICRS) implantation from January 2018 to December 2020. A minimum follow-up time of 3 months was required. Included were eyes with a clear cornea, contact lens intolerance and an unsatisfactory BSCVA. Eyes with previous ocular comorbidities other thank keratoconus were excluded. Signed informed consent was obtained from all subjects prior to surgery.

Data Collection

Preoperative demographics that were recorded included gender and age. Additional preoperative data included manifest refraction, K1, K2, minimal corneal thickness, preoperative uncorrected distance visual acuity (UCVA) and BSCVA. Operative data included whether crosslinking (CXL) was performed at the time of the procedure. Data from the postoperative period included manifest refraction, UCVA, BSCVA, K1 and K2.

Variable Thickness Intracorneal Ring Segment

The Barbara Ring VT-ICRS (Fig. 1) has a thickness profile that increases in thickness from the proximal to the distal part of the ring segment. The rationale of the design is that the ICRS is thicker parallel to the steepest axis and less thick where less correction is required.

Fig. 1: The Barbara ring variable thickness ICRS. Thickness and arc at various points of the ring are provided in the illustration

Surgical Technique

The VT-ICRS surgery was performed manually under topical anesthesia with benoxinate 0.1% (Dr. Fischer, Israel) eyedrops. Following insertion of speculum was inserted, the eye was washed with sterile 4% povidone solution (Concept, Israel), the center of the cornea was marked and a 7 mm optical zone Intacs marker was used (AJL, Spain) to mark the incision site and the tunnel position. Ultrasound pachymetry was performed to measure the corneal thickness at the incision site and at the tunnel site. A diamond knife was set to 80% depth of the corneal thickness at the incision site after the incision pocketing was performed with a Soares spreader spatula (AJL, Spain). An Intacs vacuum centering guide was inserted (AJL, Spain) and level 1 suctioning applied, thereafter a 7 mm optical zone dissector (AJL, Spain) was inserted and rotated. The VT-ICRS was inserted with forceps. No suture was used, and no contact lens was applied when only ICRS was performed. Moxifloxacin 0.3% (Vigamox, Alcon, USA) was prescribed six times daily for 1 week and then four times daily for 2 additional weeks. Prednisolone 0.1% (Pred Forte Allergan, USA) three times a day for 2 weeks was prescribed starting from day 2. If combined with CXL, the epithelium was removed from the central 8 mm of the cornea, with the assistance of 20 % alcohol. Riboflavin 0.1% without dextran (Avedro, USA) was instilled every 2 minutes, until the appearance of a strong yellow flare in the anterior chamber (after almost 20 minutes) was identified and until the thinnest corneal point as measured intraoperatively by ultrasound was >400 µm. A speculum was inserted, and the eye was irradiated for a duration of 10 minutes by ultraviolet A (UVA) at 365–370 nm, using the UVX device (Peschke Meditrade, Ltd, Germany) 9 mm beam. The light intensity was 9 mW/cm2 and the light source was 5 cm from the eye. During treatment physiological saline was instilled 5 minutes after the beginning of irradiation. A therapeutic contact lens was applied to the eye posttreatment. Postoperative treatment was identical to the post-VT-ICRS, except that prednisolone was prescribed only 3 days postoperatively four times a day only after the removal of the contact lens and complete re-epithelization was achieved.

The patients were examined at day 1 postoperatively, 1 week, 1 month, and 3 months, 6 months, and 1 year except for cases with the combined VT-ICRS and CXL (which were seen also on day 3 postoperatively).

Study Outcomes

Primary outcomes included BSCVA, UCVA and adverse events. Secondary outcomes included keratometry and manifest refraction.

Statistical Analysis

Data were analyzed with the Minitab Software, version 17 (Minitab Inc., State College, Pennsylvania, USA). For the analysis of continuous data paired t-test was used for normally distributed variables and Wilcoxon signed ranked test for nonparametric variables. Alpins’ vector analysis was conducted to report surgically induced astigmatism (SIA).1315 Standard graphs for reporting outcomes for astigmatism correction were produced using the online ASSORT group analysis calculator.16,17 Safety index and efficacy index were calculated as decimal postoperative BSCVA/preoperative BSCVA and postoperative UCVA/preoperative BSCVA, respectively. In all analyses, a two-sided p < 0.05 was considered statistically significant. All presented means are accompanied by their respective standard deviations.

RESULTS

Overall, 9 eyes of 7 patients with a mean age of 30.22 ± 8.58 (range, 21–49) years of which 85.7% (n = 6) were of male gender were included. The mean follow-up time was 9.0 ± 5.3 (range, 4–17) months. No intraoperative or postoperative adverse events were identified during the follow-up period of these patients. A single eye underwent a combined VT-ICRS and CXL procedure. Table 1 depicts the remaining baseline refractive and keratometry parameters of the patients.

Table 1: Baseline refractive and keratometry parameters of the patients
Parameter Mean ± SD Range
Age (years) 30.22 ± 8.58 21–49
LogMAR UCVA 0.95 ± 0.21 0.70–1.30
Manifest sphere (D) 1.11 ± 1.69 0–4.0
Manifest cylinder (D) −6.61 ± 2.83 0–4
K1 (D) 46.96 ± 4.59 39.85–51.87
K2 (D) 51.94 ± 5.43 45.23–58.92
LogMAR BSCVA 0.35 ± 0.10 0.18–0.48
Central corneal thickness (micron) 424.22 ± 26.06 367–452
BSCVA, best spectacle-corrected visual acuity; D, diopter; K1, flat keratometry; K2, steep keratometry; SD, standard deviation; UCVA, uncorrected distance visual acuity

At final follow-up, there was significant improvement in logMAR UCVA (from 0.95 ± 0.21 to 0.34 ± 0.31, p < 0.001), manifest sphere (from 1.11 ± 1.69 to −0.13±0.35 D, p = 0.05), manifest cylinder (from −6.61 ± 2.83 to −2.44 ± 2.26 D, p < 0.001), K2 (from 51.94 ± 5.43 to 49.20 ± 5.78 D, p = 0.01), and logMAR BSCVA (from 0.35 ± 0.10 to 0.15 ± 0.14, p = 0.002). The mean safety index was 1.68 ± 0.53 (range, 1–2.50) and the mean efficacy index was 1.24 ± 0.69 (range, 0.39–2.25). Table 2 depicts the remaining preoperative and postoperative refractive and keratometric values.

Table 2: Comparison of preoperative and postoperative refractive and keratometry parameters
Parameter Preoperative Postoperative p-value
LogMAR UCVA 0.95 ± 0.21 0.34 ± 0.31 <0.001
Manifest sphere (D) 1.11 ± 1.69 –0.13 ± 0.35 0.05
Manifest cylinder (D) −6.61 ± 2.83 –2.44 ± 2.26 <0.001
K1 (D) 46.96 ± 4.59 46.64 ± 5.25 0.63
K2 (D) 51.94 ± 5.43 49.20 ± 5.78 0.01
LogMAR BSCVA 0.35 ± 0.10 0.15 ± 0.14 0.002
BSCVA, best spectacle-corrected visual acuity; D, diopter; K1, flat keratometry; K2, steep keratometry; UCVA, uncorrected distance visual acuity

Alpins refractive vector analysis revealed a mean SIA of 4.99 ± 1.20 D (range, 3.79–7.12 D) with a mean SIA axis of 96.3 ± 42.5° (range, 25.1–142°). The SIA vector plot is presented in Figure 2. An example of a difference map of one of the patients is provided in Figure 3 with anterior segment optical coherence tomography imaging in Figure 4.

Fig. 2: Surgically induced astigmatism vector plot following variable thickness ICRS

Figs 3A and B: (A) Difference map of one of the patients before (bottom) implantation of the variable thickness ICRS demonstrating significant flattening; (B) Difference map of one of the patients after (top) implantation of the variable thickness ICRS demonstrating significant flattening

Fig. 4: Anterior segment optical coherence tomography showing placement of the variable thickness ring segment within the cornea

DISCUSSION

The current study aimed to assess the preliminary outcomes of a new VT-ICRS for the treatment of keratoconus. There were no adverse events reported following implantation and significant improvement in UCVA, manifest refraction, keratometry and BSCVA were achieved indicating that this is both a safe and effective treatment modality for keratoconus with impacted BSCVA.

Long-term stability was observed after ICRS implantation in eyes with progressive keratoconus, with 92.9% of eyes showing no progression postoperatively, suggesting a potential therapeutic effect on progression.18 Additionally, femtosecond laser-assisted Ferrara ring implantation resulted in long-term stability in a young group of keratoconus patients with a high potential for progression.19 However, instability of keratoconus was reported in 18 eyes after the implantation of Intacs and Ferrara rings. While the ICRS significantly improved visual, refractive, and topographic parameters in the short term, regression was observed after 5 years, indicating that ICRS implantation may not significantly influence progressive keratoconus in young patients with confirmed progression.20 Indeed, for stabilizing keratoconus, CXL is needed and ICRS is primarily used to improve visual acuity rather than stabilize the condition. We performed ICRS in stable or stabilized eyes by CXL only, and in cases where progression is documented, simultaneous CXL and ICRS implantation are considered. In our study, the achieved results in terms of visual acuity improvement and reduction of astigmatism remained stable starting from 1 month post operatively and throughout the follow-up duration.

In the current study, there was a significant improvement in logMAR UCVA from 0.95 ± 0.21 to 0.34 ± 0.31 (p < 0.001). Although not directly comparable, Sardiña et al. recently reported a slightly lower improvement in logMAR UCVA from 0.75 to 0.43 when assessing the AJL-pro VT-ICRS in a multicenter keratoconus study.10 Similarly, Prisant et al. reported a similar improvement in logMAR UCVA from 0.82 to 0.46 following implantation of an asymmetric thickness ICRS.12 Vega–Estrada et al., assessing outcomes in more severe keratoconus, reported a slightly more modest improvement in logMAR UCVA from 1.10 to 0.66 when assessing the VISUMRING VT-ICRS.11

Improvements in manifest refraction secondary to a reduction in central curvature of the anterior corneal surface have been reported following various classic ICRS as well as VT-ICRS implantations.2124 Similarly, the reduction in cylinder is the result of greater flattening achieved in the steepest meridian of the anterior corneal curvature. Vega–Estrada et al. reported significant reductions in median spherical equivalence (from −12.38 to −5.00 D) and sphere (from −10.35 to −2.84 D) with no significant changes in median cylinder (from −4.05 to −4.31) with the VISUMRING VT-ICRS.11 Prisant et al. reported reductions in mean spherical equivalence (from −3.85 to −1.91D), sphere (from −1.74 to −0.90 D), and cylinder (from −4.22 to −2.01 D) following asymmetric thickness ICRS.12 Sardiña et al. reported reductions in mean spherical equivalence (from −3.02 to −1.28 D), sphere (−1.56 to −0.55 D), and cylinder (from −2.92 to −2.16 D) with the AJL-pro VT-ICRS.10 In the current study, there was a modest reduction in sphere (from 1.11 ± 1.69 to −0.13 ± 0.35 D, p = 0.05) whereas there was a larger reduction in cylinder (from −6.61 ± 2.83 to −2.44 ± 2.26 D, p < 0.001).) We speculate that this is due to the thickness profile that increases in thickness from the proximal to the distal part of the ring segment.

In the current study there was a significant improvement in logMAR BSCVA from 0.35 to 0.15. Although not directly analyzed and reported in the current study, this likely reflects an improvement in irregular astigmatism and higher order aberrations. Vega–Estrada et al. reported a similar improvement in median logMAR BSCVA from 0.62 to 0.37 with the VISUMRING VT-ICRS whereas Prisant et al. reported a more modest improvement in mean logMAR BSCVA from 0.31 to 0.21 with the asymmetric thickness ICRS and Sardiña et al. reported a nonsignificant change in mean logMAR BSCVA (0.18–0.10) with the AJL-pro VT-ICRS.1012 When assessing the corneal aberrometric changes associated with the improvement in BSCVA, Sardiña et al. showed that the higher order aberration demonstrating the greatest improvement following VT-ICRS was primary coma aberration.10 Indeed, primary coma aberration is the main aberration degrading the visual acuity in keratoconus eyes and its improvement would explain the gain of spectacle corrected vision.25

The indications for ICRS include mild-to-moderate keratoconus, especially in patients who are contact lens intolerant.26 They can be used as a therapeutic option for visual improvement in patients with low vision that cannot be corrected otherwise.27 Furthermore, ICRS can also be considered in cases where it is not possible to fit and wear rigid contact lenses properly.27 However, it is important to note that ICRS may not be highly effective in advanced keratoconus with significant corneal thinning, ectasia, or opacities.7 One of the advantages of ICRS is that they are reversible and can be removed or exchanged if necessary.26 They provide a less invasive alternative to penetrating keratoplasty, improve visual acuity and corneal shape, allowing for better fitting of contact lenses or reducing the need for them.28 However, it is important to consider the potential complications associated with ICRS. Complications can include infection, corneal thinning, corneal perforation, extrusion of the segments, and induced astigmatism.29 The risk of complications can be minimized with proper patient selection, surgical technique, and postoperative management.29 It is crucial for patients to be well-informed about the potential risks and benefits of ICRS before undergoing the procedure.

In conclusion, ICRSs are a treatment option for mild-to-moderate keratoconus, especially in patients who are contact lens intolerant. They can improve visual acuity and corneal shape, providing an alternative to more invasive procedures. However, it is important to carefully consider the indications, advantages, and potential complications of ICRS before recommending them to patients.

This study has several limitations, the main ones being its retrospective nature, small sample size and preliminary nature. Furthermore, long-term outcomes are of interest to rule out potential long term complications such as ring migration, extrusion and corneal melting.30 An additional limitation is the lack of reporting on the effect of higher order aberrations. Although, similar to most studies, a more real-life surrogate of change in BSCVA was reported in its place. Last, in the current surgical technique, the tunnels were created manually and not with a femtosecond laser. As such, the findings of this study do not apply to femtosecond laser assisted VT-ICRS implantation.

In summary, the initial results of this new VT-ICRS for the treatment of keratoconus are encouraging. Prospective randomized studies are required to determine whether it has advantages over existing modalities.

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