Topographic, Aberrometric and Visual Changes After Symmetrical and Asymmetrical Intrastromal Corneal Ring Implantation in Patients with Keratoconus

Abstract

Purpose of the study: To evaluate the short-term effects of two 6.0-mm Intrastromal Corneal Ring Segment (ICRS) designs, Symmetrical (S-ICRS) and Asymmetrical (A-ICRS), on visual performance, corneal morphology and optical quality in patients with keratoconus. Methodology: This prospective study included 48 eyes of 48 patients with keratoconus implanted with either S-ICRS (n = 30) or A-ICRS (n = 18). Comprehensive ophthalmic examinations were performed before surgery and 6 months postoperatively, including manifest refraction, Pentacam tomography, corneal topometric indices, Higher-Order Aberrations (HOAs) and best-corrected High- and Low-Contrast Visual Acuity (HCVA and LCVA) under photopic and mesopic conditions, together with Contrast Sensitivity (CS). Associations between optical aberrations and visual function were also analyzed. Results: Both ICRS designs produced significant improvements in refractive error, corneal regularity and topographic parameters. Anterior corneal flattening, reduced astigmatism, improved asphericity and significant enhancement of corneal asymmetry indices (ISV, IVA, KI, CKI, IHA and IHD) were observed. Corneal HOAs decreased, particularly after S-ICRS implantation. Visual function improved under both photopic and mesopic conditions, with greater gains in mesopic LCVA and CS. Significant correlations were found between reductions in total and anterior corneal HOA root mean square values and improvements in visual acuity and contrast sensitivity, indicating that enhanced optical quality was associated with better functional outcomes. Key findings: Implantation of 6.0-mm Intrastromal Corneal Ring Segments (ICRS) significantly improved refractive status, corneal regularity and visual performance in patients with keratoconus after 6 months. Both symmetrical and asymmetrical ICRS designs produced significant anterior corneal flattening, reduced corneal astigmatism and improved corneal topographic asymmetry indices. Corneal higher-order aberrations were significantly reduced after surgery, particularly following symmetrical ICRS implantation, indicating improved optical quality. Best-corrected visual acuity and contrast sensitivity improved under both photopic and mesopic conditions, with the greatest functional gains observed under mesopic illumination. Conclusion: Implantation of 6.0 mm ICRS significantly improves corneal morphology, optical quality and visual performance in keratoconus. Both symmetrical and asymmetrical designs were effective, although their effects differed according to disease severity and ring geometry.