Asymmetric Thickness Intracorneal Ring Segments for Keratoconus

Purpose: To describe the anatomical and functional results of the implantation of asymmetric thickness intracorneal ring segments (AS-ICRS) in eyes with keratoconus and asymmetric/irregular astigmatism (type 2 - Duck - and type 3 - Snowman - phenotypes, Fernandez-Vega/Alfonso morphologic Keratoconus classification).

Materials and methods: Retrospective observational study including 19 consecutive patients (21 eyes) with keratoconus who underwent manual implantation of the Keraring^® Asymmetric ICRS (AS). Analysis included demographic and clinical data and Pentacam (Oculus^®) measurements: topographic astigmatism; topographic flat meridian (K1), steepest meridian (K2) and the maximum keratometric point (Kmax); total root mean square (RMS) and high order RMS (HOA) aberrations and comatic Zernike coefficients (Z3¹;Z3^-1) at 0º and 90º meridians.

Results: Overall mean age was 35.3±11.7 years and median follow-up was 7.1 months (range 6-12). At the end of follow-up, a significant improvement from baseline was achieved in both UDVA (0.24±0.22; p=0.017) and CDVA (0.21±0.17; p<0.001). Regarding topographic measurements, the greatest decrease was observed in K2 (2.76±1.9D; p<0.001) and astigmatism (1.97±1.5; p<0.001). Aberrometry analysis showed a reduction of 1.27±3.2µm in the total RMS (p=0.085), 0.24±0.9µm in HOA (p=0.227) and 0.78±0.5 (p<0.001) in the 90º component of comatic aberration. The procedure effects in the CDVA, topographic and aberrometric parameters were higher in type 2 cones without statistical significance (p>0.05 in all).

Conclusion: Implantation of the Keraring^® Asymmetric ICRS in keratoconus with asymmetric/irregular astigmatism allowed an improvement of several clinical, topographic and aberrometric parameters, with clinical efficacy and safety, with a tendency to a greater effect in the type 2 cones.