Changes in biomechanical properties of keratoconic corneas following intracorneal ring segment (ICRS) implantation

Abstract

AbstractPurposeStudies using Corvis ST (CST, Oculus; Wetzlar, Germany) and Ocular Response Analyser (ORA, Reichert, Depew, NY, USA) have reported significant differences between keratoconic and healthy corneas. Implantation of intracorneal ring segments (ICRS) using a femtosecond laser represents a reliable surgical option to widen the spectrum of the stage‐related therapy of keratoconus in patients with contact lens intolerance, post‐LASIK‐keratectasia or pellucid marginal degeneration (PMD). Our aim was to evaluate the ability of the Corvis ST and Ocular Response Analyser to detect the possible stiffening effect after Intacs SK (Addition Technology, Inc.) implantation in patients with keratoconus.Patients and MethodsBetween January 2018 and January 2019, ICRS were implanted in 31 eyes of 27 patients (age 31.9 ± 10.2 years) with clear central cornea. The patients had to fulfill the corneal diagnostic tests required for femtosecond laser‐assisted Intacs SK implantation in 80% depth. The following CST/ORA parameters were recorded: deformation amplitude Ratio (DA Ratio), stiffness parameter at applanation 1 (SP A1), Corvis biomechanical index (CBI), tomographic biomechanical index (TBI), Keratoconus Match Index (KMI), corneal hysteresis (CH) and corneal resistance factor (CRF) preoperatively and 6 months after the ICRS implantation.ResultsDA Ratio (5.43 ± 1.0 vs 5.52 ± 1.1, p = 0.4), SP A1 (58.76 ± 17.5 vs 59.11 ± 17.8, p = 0.4) CBI (0.96 ± 0.1 vs 0.97 ± 0.1, p = 0.3), TBI (0.98 ± 0.0 vs 0.99 ± 0.1, p = 0.3) and KMI (−0.03 ± 0.3 vs −0.17 ± 0.2, p = 0.1) did not change significantly between both time‐points. However, CH (7.96 ± 1.2 vs 7.05 ± 0.9) and CRF (6.33 ± 1.2 vs 5.35 ± 1.2) decreased significantly from preoperative to postoperative measurement time‐point (p = 0.03 for both).ConclusionBoth devices ORA and CST are supposed to analyse the dynamic behavior of the cornea during its temporary deformation by an air puff. The lack of significant changes in the standard parameters of the CST reflects the inability of this device to document the stiffening effect of ICRS in keratoconus patients. In contrast, the standard ORA parameters CH and CRF, but not the KMI, showed a significant decrease 6 month postoperatively. The meaning of those findings in relation to the progression of a keratoconus the disease has to be evaluated further.