From Synthetic to Biological Rings: CAIRS for Visual Preservation After PMMA ICRS Extrusion in Keratoconus, A Case Report

Purpose: To report the outcome of partial replacement of an extruded PMMA intracorneal ring segment (ICRS) with corneal allogenic intrastromal ring segment (CAIRS) in advanced keratoconus. Case Presentation: A patient with advanced keratoconus previously treated with a pair of Ferrara ring segments, achieved stable visual improvement for over 20 years. In 2024, extrusion of one segment occurred. The extruded PMMA segment was removed and replaced with a full-thickness CAIRS, while the second segment was left in situ. Despite technical challenges in adapting the CAIRS to the pre-existing tunnel, implantation was successful and visual acuity was preserved. Conclusion: Partial exchange of an extruded ICRS with CAIRS is feasible and may maintain prior visual and biomechanical gains, offering an alternative to complete segment removal in selected cases.