Intrastromal Corneal Rings for Myopia, Keratoconus, and Corneal Ectasia

Abstract

Intracorneal ring segments (ICRS) are devices designed to improve visual acuity, contact lens tolerance, and quality of life of patients with keratoconus. Since Barraquer's first description of intrastromal devices for correction of the eye refraction, through Colin's studies demonstrating the flattening effect and improvement of corneal asymmetry induced by ICRS, to the more modern models of progressive thickness ICRS, effectiveness, and safety have been demonstrated. The mechanism of action is explained by the Barraquer's "law of thickness" that states: "when tissue is added to the periphery of the cornea, a flattening effect is achieved." There are several types of ICRS. Their main differences lie in the arc of length, cross-sectional geometry, thickness, optical zone, and diameters. The main indications of ICRS include, but are not limited to, contact lens intolerance with poor best-corrected visual acuity, clear central cornea, and good visual acuity potential. ICRS implantation is not indicated in keratoconus patients with keratometry readings >65 D, or in pregnant women. This is an ambulatory procedure; tunnel creation can be performed with mechanical or femtosecond-assisted techniques. There is no evidence on the superiority of one technique versus the other, being both equally effective, with a theoretical advantage of safety towards the femtosecond-assisted procedure. Studies have shown a better result in patients with moderate keratoconus (Grade III-IV), with keratometry readings <57 D, as long as ICRS are implanted into an appropriate depth. Recent studies have shown an improvement of spherical equivalent with a mean change from 0.84 D to 7.6 D.