Clinical outcomes after implantation of a combination of intrastromal corneal ring segments in different optical zones in advanced keratoconus

Abstract

Purpose:

To evaluate the efficacy and safety of combined intrastromal corneal ring segment (ICRS) implantation in different optical zones for advanced keratoconus.

Methods:

This retrospective study analyzed 32 eyes from 30 patients who underwent combined implantation of an ICRS (320° arc, 200 µm) in the 5-mm zone and a high-myopia ICRS (400 µm) in the 6-mm zone. Pre- and postoperative (6 months) assessments included best-corrected distance visual acuity (BCVA), manifest refraction spherical equivalent (MRSE), keratometry (K), and asphericity (Q-value).

Results:

A total of 32 eyes from 30 patients (mean age: 31.1 ± 10.43 years) were analyzed. Significant postoperative improvements were observed in BCVA (P = 0.002), MRSE (P < 0.001), K1, K2, mean K (P < 0.001), maximum K, tomographic astigmatism, and Q-value (P < 0.001). No intraoperative or postoperative complications were reported.

Conclusions:

Combined ICRS and high-myopia ICRS implantation improves visual acuity, reduces refractive error, and enhances corneal topography in advanced keratoconus. Further studies are needed to confirm long-term stability and safety.

Keratoconus is a chronic corneal ectasia marked by progressive stromal thinning and steepening of the corneal surface, which results in irregular astigmatism and impaired vision.[1,2,3,4,5,6,7,8,9,10] The therapeutic strategy depends on the stage of the disease. In the initial phases, spectacles or contact lenses may provide acceptable visual correction.[11,12,13,14,15,16] To delay progression, corneal collagen cross-linking with riboflavin and ultraviolet light has become the standard option.[17] In more advanced stages, implantation of intrastromal corneal ring segments (ICRSs) offers a minimally invasive means to reshape the cornea and decrease curvature.[18] When structural compromise is severe and visual function cannot be restored by these approaches, corneal transplantation—either lamellar or penetrating—remains necessary.[19,20]

Because keratoplasty carries risks such as immune rejection, limited graft availability, and long recovery times, there is increasing interest in less invasive alternatives.[21] ICRS implantation has emerged as a relevant option since it alters corneal biomechanics while maintaining native tissue integrity.[18] These semicircular implants flatten the cornea, and their geometry can be tailored by adjusting thickness and arc length, allowing individualized treatment of astigmatism and corneal shape irregularities.[22] Among commercially available devices, the Ferrara ring (AJL Ophthalmic, Victoria, Spain) is one of the most frequently used, featuring a triangular cross-section and multiple size configurations.[23]

More recently, a special model named high-myopia ICRS (HM-ICRS) was introduced for keratoconus patients with significant myopia.[24] Also developed by AJL Ophthalmic, this device was created to improve refractive correction, particularly in cases with thin corneas or contraindications to excimer laser procedures.

A novel surgical strategy has been proposed for advanced keratoconus: combining a conventional ICRS placed at the 5-mm optical zone with an HM-ICRS implanted concentrically at the 6-mm zone. This wider distribution of intracorneal material is expected to induce greater flattening than isolated ICRS insertion. Nevertheless, there are no published studies systematically analyzing the safety and effectiveness of this combined concentric approach.

Considering the rising demand for minimally invasive, reversible, and tissue-preserving solutions for keratoconus, this investigation was designed to evaluate the outcomes of concentric ICRS implantation. We hypothesize that the combined technique provides enhanced corneal flattening and adequate visual rehabilitation in individuals with advanced keratoconus.

Methods

This retrospective observational study was based on a review of medical records from patients who underwent combined implantation of ICRS and HM-ICRS to treat advanced keratoconus at a specialized ophthalmic hospital in Brazil. The study was approved by the Ethics Committee of a Federal University under the code CAAE 31320920.8.0000.8058 and adhered to the principles of the Declaration of Helsinki. Informed consent was obtained from all participants or legal guardians to use their medical information in this research.

Inclusion criteria included the diagnosis of advanced keratoconus treated with combined implantation of a Ferrara ring with a 320° arc and 200 micrometers of thickness and an HM-ICRS with 400 micrometers of thickness, either in one or two surgical stages. Advanced keratoconus was defined by a maximum keratometry (K) value greater than 60 D and classified as A4 or B4 according to the ABCD staging system by Belin on the Pentacam Corneal Tomography (Oculus Optikgeräte, Wetzlar, Germany). Additional criteria included a best-corrected distance visual acuity (BCVA) of 0.3 logMAR or worse, contact lens intolerance, prior corneal transplantation indication, and a minimum follow-up period of 6 months.

Exclusion criteria included conditions that could interfere with the study outcomes, such as cataracts, corneal scars, previous eye surgery (including corneal cross-linking), systemic autoimmune diseases, severe dry eye, active allergic conditions, fundoscopic abnormalities affecting visual acuity (e.g., diabetic retinopathy), advanced glaucoma, pregnancy or lactation, mental disabilities, Down syndrome, and amblyopia. Individuals with less than 90 days of follow-up were also excluded.

All surgeries were performed by a single surgeon (PF), under topical anesthesia, using the Ziemer Z8 femtosecond laser (Ziemer Ophthalmic Systems AG, Switzerland) to create corneal tunnels at a depth corresponding to 70% of the thinnest point’s thickness along the ring path, ensuring precise centralization on the Purkinje reflex. The internal diameter of the tunnel created was 4.4 mm, and the external diameter was 5.73 mm; the energy used to create the tunnel and incision was 1.3 mJ, and the incision was made at the 90° meridian in all cases. The laser application time was 15 seconds, and the ICRSs were implanted immediately afterward. Fig 1 demonstrates the usual late postoperative appearance of a combined implant of HM-ICRS and ICRS of 320° arc length. The internal diameter of the tunnel created was 5.82 mm, and the external diameter was 7.68 mm for the HM-ICRS.

Figure 1.

Biomicroscopy Photograph of the Late Postoperative Anterior Segment of Combined HM-ICRS + ICRS Implantation. Biomicroscopy photograph of the anterior segment of a patient who underwent combined implantation of intracorneal ring segments. The image shows two concentric ring segments: an external standard ICRS and an internal HM-ICRS with a smaller inner diameter, designed for additional myopia correction. The cornea exhibits good integration of both segments, with no visible complications

We reviewed the medical records of patients who underwent pre- and postoperative ICRS. The same ophthalmologist conducted All evaluations and surgeries 1 and 3 months after the procedures. The records included BCVA, mean refractive spherical equivalent (MRSE), and Scheimpflug tomography data, including K1, K2, mean and maximum K, tomographic astigmatism, and asphericity (Q value). For this study, due to the nature of the disease and subsequent difficulties to obtain accurate refractive measures, BCVA was considered as the best achievable visual acuity, using contact lenses, spectacles, or a phoropter.

The sample size adequacy was evaluated retrospectively using the G.Power® 3.1 program (Franz Faul, Universitat Kiel, Germany) to ensure sufficient statistical power for the variables analyzed. A minimum of 19 eyes (95% CI: 11 to 26) was required at a 5% significance level, with a 95% confidence interval and a statistical power of 99% to detect significant differences.

Statistical analyses were performed on data tabulated in CSV spreadsheets using the JASP v. 0.18.3 program (The JASP Team, Amsterdam, Netherlands). Descriptive frequency, centralization, and distribution measures were presented for the data collected. The normality of the data was verified using the Kolmogorov–Smirnov test. The parameters evaluated over time were compared using Student’s t-test and Friedman’s repeated-measures ANOVA with Bonferroni’s post-hoc correction. A significance level of 5% (P < 0.05) was adopted in all analyses. For the late follow-up period evaluations, data from the latest evaluation with at least 6 months from the surgery were used. The Double Angle Plot for astigmatism vectorial analysis was generated using the Excel spreadsheet the American Society of Cataract and Refractive Surgery provided.^[A]

Results

This study analyzed 32 eyes from 30 patients who underwent concentric implantation of ICRS and HM-ICRS between March 2020 and April 2024. The median follow-up time was 11 months (range: 6–24 months). Table 1 summarizes the preoperative and postoperative refractive and tomographic characteristics of the participants, while Fig. 2 illustrates the differences between pre- and postoperative evaluations for visual and tomographic outcomes. Of the 32 eyes included, 14 (43.75%) were right eyes. Among the 30 participants, 15 (50%) were female, with a mean age of 31.1 ± 10.43 years.

Table 1.

Clinical and tomographic variables

		Preoperative		1mo Postop.		3mo Postop.		Late Postop.
BCVA (LogMAR)		0.58±0.31 (n=24)		0.47±0.25 (n=21)		0.37±0.23 (n=25)*		0.34±0.17 (n=21)*
MRSE (D)		-10.5±6.52 (n=28)		-7.18±5.54 (n=18)*		-6.08±5.45 (n=25)*		-5.88±4.74 (n=19)*
Mean K (D)		58.79±10.95 (n=32)		50.11±11.46 (n=27)*		49.38±10.18 (n=31)*		49.34±9.51 (n=32)*
Max K (D)		68.18±13.72±(n=32)		63.67±12.624 (n=27)*		63.42±10.32 (n=31)*		61.96±10.30 (n=32)*
K1 (D)		56.63±10.88 (n=32)		48.56±11.43 (n=27)*		47.81±10.13 (n=31)*		47.89±9.66 (n=32)*
K2 (D)		61.19±11.2 (n=32)		51.84±11.57 (n=27)*		51.13±10.42 (n=31)*		50.96±9.46 (n=32)*
T. Astig.(D)		4.58±3.09 (n=32)		3.30±2.24 (n=27)*		3.32±2.50 (n=31)*		3.07±2.27 (n=32)*
Asphericity (Q)		-1.25±0.72 (n=32)		-0.05±1.36 (n=27)*		-0.08±1.38 (n=31)*		-0.01±1.22 (n=32)*

Values are presented as mean±standard deviation. Late postoperative period was defined as the latest follow-up after 6 months. Mo: month. Postop: Postoperative. BCVA: Best Corrected Visual Acuity. K: Keratometry. K1: Flat K. K2: Steep K. T. Astig.: Tomographic Astigmatism. *Statistically significant difference from preoperative values (P<0.05)

Figure 2.

Clinical and Tomographic Postoperative Comparisons after Intracorneal Ring Segment Implantation. Comparative analysis of preoperative and postoperative clinical and tomographic parameters in patients undergoing combined intracorneal ring segment implantation. The error bars represent. (a) Best-corrected visual acuity (BCVA), showing significant postoperative improvement in both groups. (b) Corneal asphericity, demonstrating a reduction postoperatively, indicative of a more regular corneal surface. (c) Flat keratometry (K1), showing a decrease in corneal curvature. (d) Steep keratometry (K2), with a postoperative reduction in curvature. (e) Mean keratometry (Kmean), reflecting an overall decrease in corneal power. (f) Maximum keratometry (Kmax), with a postoperative decrease, indicating a smoothing effect on the corneal surface

Statistically significant improvements were observed in visual parameters following the combined implantation of intrastromal corneal ring segments. BCVA improved from a preoperative mean of 0.58 ± 0.31 logMAR to 0.34 ± 0.17 logMAR postoperatively (P < 0.001), while MRSE improved from -10.5 ± 6.522 D to -5.882 ± 4.74 D (P = 0.005).

Tomographic parameters also showed significant improvement. The mean K readings decreased from 58.79 ± 10.95 D to 49.34 ± 9.51 D (P < 0.001), while the maximum K readings reduced from 68.18 ± 13.72 D to 61.96 ± 10.30 D (P < 0.001). Similarly, both principal meridians demonstrated improvement: K1 changed from 56.63 ± 10.88 D to 47.89 ± 9.66 D (P < 0.001), and K2 from 61.19 ± 11.20 D to 50.96 ± 9.46 D (P < 0.001). Tomographic astigmatism decreased from 4.58 ± 3.09 D to 3.07 ± 2.27 D (P = 0.004). Additionally, asphericity (Q-value) improved substantially, shifting from -1.25 ± 0.72 preoperatively to -0.01 ± 1.22 postoperatively (P < 0.001).

The vectorial analysis of astigmatism is presented in Fig. 3, showing a reduction in magnitude and a high degree of axis stability following intracorneal ring segment implantation.

Figure 3.

Double Angle Plot for Corneal Astigmatism Analysis. Vectorial representation of preoperative (a) and postoperative (b) corneal astigmatism following combined intracorneal ring segment implantation. Each concentric circle represents 4 D steps. The blue line represents the 95% confidence interval for the dataset, while the red line represents the 95% confidence interval around the centroid. Preoperatively, the centroid was 1.77 D at 78° with a variability of ± 5.34 D, and the mean astigmatism magnitude was 4.62 ± 3.06 D. Postoperatively, the centroid shifted to 1.40 D at 71° ± 3.58 D, while the mean astigmatism magnitude decreased to 3.07 ± 2.23 D. These findings indicate a significant reduction in overall astigmatism magnitude, suggesting improved corneal regularity with a slight centroid shift, reflecting good axis stability after the procedure

No intraoperative or postoperative complications were reported in this study.

Discussion

The results suggest that both treatment strategies can effectively reduce corneal curvature, asphericity, and astigmatism. Additionally, this retrospective study observed no complications, reinforcing the safety of this approach.

Several earlier reports excluded keratoconus patients with keratometric values above 60 D from ICRS surgery, citing reduced predictability and higher failure rates in advanced disease.[15,16,17] Others emphasized the risk of adverse events, such as nonhealing epithelial defects, anterior or posterior perforations, segment displacement, and extrusion.[25,26] The development of femtosecond laser channels, however, has markedly increased both accuracy and safety, broadening the indications for ICRS even in severe cases.[27] Furthermore, newer segment geometries, including long-arc designs and reduced optical zones, have been associated with greater corneal flattening and more regular topographic outcomes.[23]

In this context, Soares et al.[21] reported that long-arc ICRS can serve as a safe and effective alternative for delaying or even avoiding corneal grafting in advanced keratoconus. Their series demonstrated consistent functional and anatomical improvements: BCVA improved from 0.63 ± 0.29 to 0.31 ± 0.16 logMAR, while keratometric indices showed significant reductions (K1 from 54.41 ± 4.46 D to 49.36 ± 4.11 D, K2 from 61.15 ± 4.37 D to 53.71 ± 4.05 D, mean K from 57.55 ± 4.17 D to 51.44 ± 3.94 D, and maximum K from 69.80 ± 8.20 D to 63.43 ± 6.31 D). The corneal asphericity also improved from -1.57 ± 0.35 to -0.77 ± 0.56. In our cohort of patients with maximum keratometry above 60 D, combined implantation of HM-ICRS with standard ICRS similarly produced significant flattening of K1, K2, and mean K values, along with meaningful BCVA gains, suggesting that this dual approach may postpone the need for transplantation while enhancing corneal regularity.

Rocha et al.[28] recently compared various therapeutic strategies for advanced keratoconus, underscoring the importance of a stepwise, indication-based approach. They observed complication rates of 14.28% following DALK and 17.86% among patients unable to adapt to contact lenses. By contrast, the ICRS group experienced no complications, echoing our own findings. Their analysis also showed visual improvement in 77% of patients fitted with scleral lenses, 57% after ICRS surgery, and 70% post-DALK. Despite these gains, 42.85% of DALK and 53.85% of ICRS patients required additional interventions. The best corrected visual acuity of 20/25 was eventually achieved in 85% of DALK and 72% of ICRS cases. Importantly, because scleral lenses do not arrest disease progression, complementary interventions remain necessary in progressive keratoconus.

To our knowledge, no previous work has specifically assessed the concentric combination of HM-ICRS and conventional ICRS in the same cornea. Nevertheless, Hashemi et al.[29] described five eyes that underwent a hybrid approach using an INTACS segment with an additional Keraring. They noted further flattening of up to 4.4 D and improvement in vision in four of the cases. Although the implant models and surgical techniques differ, their observations support the rationale that adding a secondary intracorneal segment can potentiate the effect of the primary implant.

Coscarelli et al.[24] investigated HM-ICRS in high myopic patients, reporting reductions of approximately 4 D in spherical equivalent and 2.9 D in mean keratometry. These changes were smaller than those observed in our study, probably reflecting differences in baseline characteristics, since their cohort did not include keratoconus cases and presented a mean K of only 44.4 ± 1.53 D (maximum 47.2 D). Even so, their findings highlight the potential of HM-ICRS for refractive correction, consistent with the significant MRSE improvement we documented.

Overall, several authors have confirmed that long-arc ICRS can reduce corneal steepening in advanced keratoconus, with mean keratometric flattening between 4 and 9 D.[24,29,30,31,32,33] Torquetti et al.[30] additionally documented an average increase of 0.84 in Q-value, which is in agreement with our results and further supports the efficacy of this surgical strategy. However, direct comparison across studies remains limited by heterogeneity in patient profiles and clinical protocols.

The clinical implications of these findings are particularly relevant for decision-making in advanced keratoconus management. The combined implantation of ICRS and HM-ICRS appears especially beneficial in patients with severe myopia and highly irregular corneal topography, who might otherwise be considered candidates for keratoplasty. In cases where contact lens adaptation is difficult due to corneal asymmetry, this approach can improve both visual quality and topographic regularity, potentially delaying or even avoiding the need for corneal transplantation. The results observed with simultaneous implantation show possible advantages of addressing multiple optical zones in a single procedure.

In our cohort, despite the significant improvements in corneal regularity and keratometric parameters, a substantial residual refractive error persisted in several eyes—consistent with the advanced ectatic profile of this population. Consequently, some patients may still require contact lens wear to achieve optimal visual performance, including the possible need for mini-scleral lenses. Importantly, ICRS implantation typically improves corneal symmetry and surface regularity, which is known to increase contact lens tolerance and reduce the complexity of fitting in postoperative keratoconus eyes.[18] Conversely, patients who remain intolerant to contact lenses, or in whom adequate optical correction cannot be achieved, may particularly benefit from this surgical strategy as the improved corneal architecture can offer meaningful visual rehabilitation while delaying the need for keratoplasty.

Another alternative for managing the residual refractive error in keratoconus is the implantation of phakic intraocular lenses, which has shown favorable outcomes in selected patients with stable ectasia and sufficient endothelial reserve.[34,35] Phakic intraocular lenses can effectively correct high myopia and regular astigmatism; however, they are less suitable when corneal irregularity predominates, or when the visual limitation arises primarily from higher-order aberrations rather than spherical or cylindrical components. In contrast, the combined implantation of standard ICRS and HM-ICRS directly addresses the biomechanical and geometric abnormalities of the ectatic cornea, aiming to regularize the optical surface rather than compensate for its irregularity, being suitable for this cohort, which consisted of highly irregular corneas with advanced ectatic deformation.

This study aimed to assess the clinical outcomes of combined ICRS and HM-ICRS implantation in advanced keratoconus, considering the growing demand for minimally invasive and reversible treatments and the current lack of scientific data on concentric ICRS implantation. The results confirmed our hypothesis that this technique provides superior corneal flattening and visual rehabilitation with significant improvements in keratometric parameters, asphericity, and best-corrected visual acuity, particularly in the simultaneous implantation group. While the absence of complications in this sample and the promising outcomes are encouraging, the long-term safety and efficacy of the intervention must be confirmed in future studies. These findings should be interpreted in light of the inherent limitations of the present study, including its retrospective design, the absence of a control group, the relatively short follow-up period, the heterogeneous timing of implantation, and the need for further evaluation of long-term stability. Future prospective, randomized studies with larger sample sizes are necessary to refine patient selection criteria, optimize nomograms, and ensure the technique’s widespread reproducibility in different clinical settings.

Conclusions

Combined implantation of standard ICRS and HM-ICRS in different optical zones was evaluated in patients with advanced keratoconus and was associated with changes in clinical and tomographic parameters during follow-up. Additional prospective controlled studies with longer follow-up are necessary to further evaluate this approach.

Authors’ contributions

Jordana Sandes Barbosa Soares – Concept, Design, Definition of Intellectual Content, Clinical Studies, Data Acquisition, Manuscript Review. Mateus Lins dos Santos – Literature Search, Data Analysis, Statistical Analysis, Manuscript Preparation, Manuscript Editing. Leonardo Torquetti Costa - Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review. Edna Motta Almodin - Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review. Bernardo Kaplan Moscovici - Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review. Guilherme Ferrara – Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review. Sandro Antonini Coscarelli Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review. Paulo Ferrara – Concept, Design, Clinical Studies, Data Acquisition, Manuscript Review.

Ethical approval and informed consent statements

This study was approved by the Federal University of Goiás Research Ethics Committee under the code CAAE 31320920.8.0000.8058. All participants have agreed with their participation in this study and its publication after detailed and accessible verbal explanation and by signing a written informed consent form. All data used in this study was anonymized.

Data availability statement

Anonymized data used in this study will be provided upon contact with the corresponding author, given reasonable request.

Conflicts of interest

PF has commercial interests associated with Ferrara Rings. The remaining authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Additional resources

A. American Society of Cataract and Refractive Surgery (ASCRS). Astigmatism Double Angle Plot Tool [Internet]. Available from: https://www.ascrs.org/tools/astigmatism-double-angle-plot-tool.

Funding Statement

Nil.