Intracorneal Ring Segments in Keratoconus: A Narrative Literature Review.

Background: Keratoconus is a bilateral, non-inflammatory corneal ectasia characterized by progressive thinning and conical protrusion, leading to irregular astigmatism, usually in association with high myopia. Visual rehabilitation options include corneal collagen cross-linking (CXL), rigid gas permeable contact lenses, intracorneal ring segments (ICRS), phakic intraocular lenses, and corneal transplantation. ICRS are synthetic, biocompatible implants or allogenic corneal tissue, designed to reduce corneal curvature and optimize the refractive profiles. Initially used in 1978 to treat myopia, their role in keratoconus was established in 2000. This review explores ICRS types, surgical techniques, and emerging developments. Methods: A literature review was conducted using PubMed. A total of 117 peer-reviewed manuscripts, including review articles, randomized controlled trials, case series, and reports, were analysed. Reference lists of publications were also reviewed. Results: ICRS types include MyoRings, KeraRings, Ferrara Rings, and Intacs, each with unique design characteristics and implantation methods. Corneal allogenic intrastromal ring segments represent the latest innovation in ICRS. Femtosecond laser-assisted tunnel creation offers improved control over stromal depth and uniformity, reducing complications compared to mechanical dissection. Studies indicate slight corneal stiffening post-ICRS implantation, with no significant changes in intraocular pressure. Topographic changes post-ICRS show significant corneal flattening and reduction in astigmatism. Complications include epithelial defects, segment migration, and keratitis, but long-term follow-up reveals low rates of serious adverse events. Conclusion: ICRS provide an effective option for enhancing vision in select keratoconus patients, ultimately lowering the chances of requiring a corneal transplant. They are of particular use in those intolerant to contact lenses and without central corneal scarring. Future research should focus on long-term outcomes. Combining ICRS with other procedures like CXL may enhance outcomes, though careful patient selection is crucial.