Comparative Study of Asymmetric Versus Non-asymmetric Intrastromal Corneal Ring Segments for the Management of Keratoconus

Abstract

PURPOSE: To compare the outcomes obtained with models of asymmetric and non-asymmetric intracorneal ring segments (ICRS) in keratoconic eyes with asymmetric topo-graphic patterns. METHODS: In this prospective observational study, ICRS were implanted alternately in patients with the same tomographic patterns of keratoconus assigned to four groups. Patients with the “duck” phenotype received one asymmetric or non-asymmetric ICRS and patients with the “snowman” pheno-type received two asymmetric or non-asymmetric ICRS. Visual, refractive, astigmatism, keratometric, and corneal aberrometry changes were evaluated over a 6-month follow-up period. RESULTS: Sixty-eight eyes were analyzed. No significant difference was observed between the use of one asymmetric and one non-asymmetric ICRS in duck phenotypes. In snowman keratoconus, the inferior-superior index decreased significantly ( P = .03) with asymmetric but not with non-asymmetric ICRS implantation. Total corneal higher order aberrations and coma rates were lower, but not significantly so, after the implantation of two asymmetric ICRS in snowman phenotypes (2.85 ± 0.89 to 2.60 ± 0.91 µm, P = .20 and 2.64 ± 0.93 to 2.39 ± 0.98 µm, P = .21), and significantly higher after the implantation of two non-asymmetric ICRS (2.56 ± 1.28 to 3.08 ± 1.62 µm, P = .02 and 2.34 ± 1.27 to 2.84 ± 1.62 µm, P = .02). CONCLUSIONS: Asymmetric ICRS did not improve the outcomes of ICRS implantation in duck keratoconus. However, the implantation of two asymmetric ICRS was more effective than that of two non-asymmetric ICRS for decreasing vertical asymmetry and preventing increases in corneal aberration in the snowman phenotype of keratoconus. [ J Refract Surg . 2021;37(8):552–561.]

Customized corneal allogenic intrastromal ring segments (CAIRS) for keratoconus with decentered asymmetric cone

“…[ 1 2 3 4 5 6 7 8 9 10 11 ] However, many topographical characteristics make customization of intrastromal segments more desirable. [ 24 25 26 27 28 29 30 31 ] In this case series, we created tapered segments for patients with pericentral or paracentral decentered cones who showed gradation of keratometric values with one side being steeper than the other. We attempted to do this by varying the volume of tissue implanted in different zones – adding more volume where greater flattening was required and less where less flattening was required.…”

“…Asymmetric synthetic ICRS have previously been reported to regularize the corneal shape and result in appreciable visual improvement in patients with a significant difference between corneal topographic and comatic axes. [ 25 26 27 28 29 30 31 ] These asymmetric segments are available as fixed combinations of arc length, diameter, thickness variation, width variation, and in clockwise and anti-clockwise versions. Moreover, the thickness changes at a uniform rate from one end to the other, without varying stretches of uniform thickness as we were able to do in the case of CAIRS.…”

Asymmetric Intrastromal Corneal Ring Segments with Progressive Base Width and Thickness for Keratoconus: Evaluation of Efficacy and Analysis of Epithelial Remodeling

“…In this study, primary coma, which is known to be the principal clinically relevant high-order aberration in keratoconic corneas [ 31 ], improved significantly, by 38.8%, after AJL PRO + implantation. Many studies of symmetric or asymmetric ICRS treatment have reported a significant improvement in asymmetric aberrations, such as primary coma and coma-like aberrations, which are known to have a negative effect on vision quality [ 9 , 11 , 32 , 33 ].…”

“…ICRSs may be symmetric or asymmetric, with different arc lengths, diameters, cross-sectional shapes, thicknesses and widths. Symmetric ICRS implantation has yielded good refractive and topographic astigmatism correction in patients with asymmetric keratoconus but does not optimally manage coma-like aberration in these patients, potentially limiting visual improvement [ 8 , 9 , 10 , 11 ]. Different types of ICRSs have recently been developed for the treatment of asymmetric keratoconus.…”

“…The thickness or width of these segments varies so as to treat the keratoconus heterogeneously, targeting certain areas of the cornea, according to the phenotype. Asymmetric ICRS implantation has resulted in good visual, refractive and topographic outcomes, with a particularly large decrease in coma-like aberration [ 6 , 9 , 12 , 13 , 14 , 15 ].…”