Evaluation of dynamic corneal response parameters and the biomechanical E-staging after Intacs® SK implantation in keratoconus

Purpose: This retrospective longitudinal study evaluated the biomechanical E-staging in KC corneas before and after intracorneal ring segment (ICRS) implantation (Intacs (R) SK, Addition Technology, Illinois, United States). Methods: Biomechanical E-staging for ectatic corneal diseases was applied retrospectively on 49 KC corneas of 41 patients who underwent ICRS implantation. The main outcome parameters included the Corvis Biomechanical Factor (CBiF, the linearized Corvis Biomechanical Index and the biomechanical parameters included), the resulting biomechanical E-staging, the stress-strain index, thinnest corneal thickness (TCT), maximal anterior keratometry (Kmax), and the anterior radius of curvature (ARC). They were evaluated at 1.9 +/- 1.1 months preoperatively and postoperatively after 2.8 +/- 0.7, 5.8 +/- 1.0, and 10.6 +/- 2.3 months. Results: The CBiF decreased (4.9 +/- 0.5 | 4.7 +/- 0.5, P = 0.0013), and the E-staging increased significantly (2.8 +/- 0.8 | 3.1 +/- 0.9, P = 0.0012, paired t-test) from preoperatively to the first postoperative follow-up. The difference remained significant after 6 months; however, there was no more difference after 11 months. TCT was stable, whereas Kmax and ARC significantly decreased after ICRS implantation (TCT: 464 +/- 49, 470 +/- 51, 467 +/- 38, 461 +/- 48; Kmax: 56.3 +/- 4.5, 54.7 +/- 4.5, 54.2 +/- 4.8, 54.1 +/- 4.3; ARC: 51.5 +/- 3.4, 48.3 +/- 3.8, 48.6 +/- 3.0, 48.6 +/- 3.2 preoperatively and 3, 6, and 11 months postoperatively, respectively). Besides Kmax and ARC, Ambrosio's relational thickness to the horizontal profile (ARTh) was the only parameter that was significantly lower than preoperatively at any follow-up (P <= 0.0024, Wilcoxon matched-pairs test). Conclusion: Intacs (R) SK implantation results in an increasing biomechanical E-staging in the first postoperative months with stabilization near preoperative values after 1 year. Significantly lower ARTh values at any follow-up document the ICRS effect and contribute to a slightly higher postoperative biomechanical E-staging value.