New approaches of intracorneal ring segments implantation for asymmetric keratoconus treatment: A case series

Dear Editor, Keratoconus is a corneal ectasia causing irregular astigmatism and visual impairment. Intrastromal corneal ring segment (ICRS) implantation is reversible to improve corneal shape and visual function. However, traditional nomograms often prioritize implantation in the steepest corneal area and can fail in highly asymmetric cases, leading to suboptimal outcomes. Concentric ICRS placement offers a tailored approach to address these limitations, improving corneal regularity and visual results in challenging scenarios.[1–5] Case Summaries Case 1 A 40-year-old male presented with grade 4 keratoconus in the left eye (OS) after prior ICRS implantation with suboptimal results. The initial segment was positioned in a 6 mm zone, reducing its flattening effect. A 210° ring segment was added concentrically in the 5 mm zone. Postoperative assessments revealed improved corneal flattening, reduced comatic aberration (from 4.2 µm to 2.1 µm), and uncorrected distance visual acuity (UDVA) improvement to 20/20. Corneal symmetry was significantly enhanced, as evidenced by reduced topographic irregularity indices [Table 1 and Fig. 1].Figure 1: (a) Comparison between preoperative examination imaging (left) and postoperative imaging after implantation of a 140/25 externalized ICRS (center). (b) Pentacam (Oculus, Wetzlar, Germany) tomography of ICRS localization in an externalized optical zone. (c) Comparison between the patient’s preoperative examination imaging (left), postoperative examination imaging following the implantation of a 140/25 externalized ICRS (center), and postoperative examination imaging following the implantation of a 210/25 ICRS internally concentric to the first implant (right). (d) Comparison between the patient’s coma preoperatively (left), postoperatively after implantation of a 140/25 externalized ICRS (center), and postoperatively after implantation of a 210/25 ICRS internally concentric to the first ICRS (right). Improvement in the comatic aberration is apparent. ICRS, intrastromal corneal ring segment. (e) Images from the patient’s preoperative OD examination. (f) Differential maps compare the patient’s preoperative and postoperative examinations before and after concentric ICRS implantation. (g) A comparison between the patient’s coma in the preoperative examination imaging (left) and the postoperative imaging, following implantation of a 140/25 externalized ICRS and an internally concentric 210/25 ICRS (right). Improvements in the comatic aberration are visible. ICRS, intrastromal corneal ring segment; OD, right eye. (h) Case 3 preoperative and postoperative optic imaging. (i) Four sagittal maps of an oval keratoconus from a Ferrara ring segment (Ferrara Ophthalmics, Belo Horizonte, Brazil) nomogram. (j) Positioning of a concentric ICRS, visualized using a slit lamp (right) and centered in Pentacam (Oculus, Wetzlar, Germany) tomography (left).Table 1: Summary of all casesCase 2 A 36-year-old male with enantiomorphic keratoconus underwent concentric implantation of 210° and 140° segments in the right eye (OD). Preoperative coma aberration was significant (3.046 µm). Postoperatively, asymmetry and coma were markedly reduced, leading to a visual improvement of 20/25. Aberrometric analysis indicated a 45% reduction in total higher-order aberrations (HOAs) and a 38% reduction in coma, contributing to improved visual quality [Table 1 and Fig. 1]. Case 3 A 23-year-old male with advanced keratoconus in OS received a 210° segment in the 6 mm zone and a 140° segment in the 5 mm zone. This configuration corrected astigmatism, reduced irregularity indices, and improved UDVA to 20/25, enabling functional independence from corrective lenses. Postoperative analysis revealed stabilization of the keratoconic progression over a 1-year follow-up period [Table 1 and Fig. 1]. Discussion Concentric ICRS implantation represents an innovative solution for challenging asymmetric keratoconus cases. This technique achieves significant corneal regularization and visual rehabilitation by targeting specific optical zones. Our cases demonstrated enhanced visual acuity, reduced HOAs, and improved corneal symmetry compared to prior treatments.[1–5] Traditional ICRS nomograms often fall short in highly asymmetric keratoconus. Our cases illustrate that strategic segment placement tailored to the patient’s unique corneal morphology can optimize outcomes. Adding a 210° segment, complementing an existing 140° implant, enhances flattening in critical zones, particularly in eyes with significant coma aberrations. This tailored approach also minimizes the risk of suboptimal visual outcomes commonly associated with generic nomograms.[1–5] Recent literature supports the utility of combined ICRS configurations in reducing coma and astigmatism. Studies report coma reductions of up to 51% and mean best corrected visual acuity improvements of 0.12 to 0.21 logMAR postoperatively. Our results align with these findings, with some cases achieving over 45% coma reduction and notable visual enhancements. This highlights the importance of individualized strategies in managing complex keratoconus cases.[1–5] Further investigation into the safety and long-term efficacy of concentric ICRS implantation is warranted. This technique has shown promise in addressing the limitations of conventional nomograms, expanding therapeutic possibilities for patients with unsatisfactory outcomes from standard ICRS protocols. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.