Corneal Biomechanical Changes Following Corneal Allogenic Intrastromal Ring Segment (Cairs) Implantation

Corneal Allogenic Intrastromal Ring Segments (CAIRS) implantation requires partial thickness radial incision(s) to the surface and a lamellar ring cut. Corneal incisions are known to biomechanically weaken the cornea and there is concern that CAIRS may negatively impact the biomechanical integrity of the keratoconic cornea.

Case series. 

Common biomechanical markers: stiffness parameter at the first applanation (SP-A1), deformation amplitude (DA), integrated radius (IR), Ambrosio relational thickness horizontal (ARTh), and stress-strain index (SSI) were measured prior to, and after CAIRS implantation in 15 eyes of 13 patients. Of the 15 surgeries, 3 were combined with corneal cross-linking (CXL), the remaining 12 surgeries consisted of CAIRS implantation alone. The surface incision was on average 1.3 mm in length and the lamellar cut placed at an average depth of 230 microns [192,300].

Following CAIRS implantation, SP-A1 measured the same or stiffer in 12/15 (80%) of surgeries (stiffer in 33%), DA the same or stiffer in 13/15 (87%) of surgeries (stiffer in 40%), IR the same or stiffer in 12/15 (80%) of surgeries (stiffer in 60%), ARTh the same or thicker in 10/15 (67%) of surgeries (thicker in 33%), SSI the same or stiffer in 12/15 (80%) of surgeries (stiffer in 67%). The three surgeries wherein immediately sequential CXL was performed did not differ significantly from the CAIRS only surgeries (Mann-Whitney u-test >0.05) and data was pooled as a result. The mean for each parameter was not statistically significantly different from pre-op to post-op.

This case series does not demonstrate a negative impact by CAIRS corneal incisions. Most biomechanical markers were the same or improved following CAIRS implantation. ARTh demonstrated the greatest weakening with 33% of cases worsening after implantation. The interpretation of biomechanical measurements in the keratoconic cornea remains difficult.