INTRASTROMAL RING SEGMENT IMPLANTATION RESULTS IN CORNEAL MECHANICAL STRENGTHENING VISUALIZED WITH OPTICALCOHERENCE ELASTOGRAPHY

To quantify the mechanical impact of intracorneal ring segment (ICRS) implantation of different dimensions in an ex vivo eye model.

OPTIC team, Computer Vision Laboratory, ETH Zurich, Switzerland and ELZA Institute, Dietikon/Zurich, Switzerland

A total of 30 enucleated porcine eyes were obtained and assigned either to ICRS implantation (thickness 300μm, angle 120°, 210° or 325°), tunnel creation only or virgin control. For mechanical evaluation, each eye globe was mounted on a customized holder and intraocular pressure (IOP) was increased in steps of 0.5 mmHg from 15 to 17 mmHg, simulating physiologic diurnal IOP fluctuations. At each step, an optical coherence tomography volume scan was recorded. Deformations between subsequent scans, as well as the locally induced axial strains were analyzed using a vector-based phase difference method. The effective E-modulus was derived from the overall induced strain as a measure of global mechanical impact.

ICRS implantation increased the effective E-modulus from 146 and 163 kPa in virgin and tunnel-only eyes to 149, 192 and 330 kPa in eyes that received a 5 mm optical zone ICRS with 120°, 210° and 325° arc length, respectively, and to 209 kPa in a 6 mm optical zone ICRS with 325° arc length. The most consistent effect was a shift towards positive strains in the posterior stroma by 0.1 to 0.46 ‰ (factor 1.15 to 2.15) after ICRS surgery.

ICRS implantation reduces the overall tissue strain under the load of the IOP and provokes posterior tissue relaxation. This effect is more dominant the longer the arc length and the smaller the optical zone of the ICRS is. ICRS have not only a geometrical, but also a mechanical impact on corneal tissue. This behavior might have clinical implications when ICRS implantation is performed in biomechanically weakened keratoconus corneas.