325° Arch-Length Intracorneal Ring Implantation Strain Maps Visualized With New Optical Coherence Elastography

The objective of this study was to record the axial corneal strain field in the cornea that resulted directly after creating a stromal tunnel as well as after implanting an intracorneal ring segment (ICRS).

Swiss federal institute of technology

Freshly enucleated porcine eyes were obtained and assigned either to ICRS implantation, to tunnel creation only or to virgin control. Immediately after manual tunnel creation and ICRS positioning, respectively, the entire eye globe was mounted within a customized holder and intraocular pressure (IOP) was adjusted to 15 mmHg. Then, IOP was increased in steps of 1 mmHg to 20 mmHg and decreased again. At each step, an optical coherence tomography volume scan was recorded. Displacements between subsequent scans were retrieved using a vector-based phase difference method. The induced corneal strain in axial direction was determined by taking the axial gradient. In addition, corneal surface was detected and sagittal curvature maps computed.

Corneal tissue presented a localized compressive strain in the direct vicinity of the stromal tunnel, which was independent of the sign of IOP change. The central and peripheral (exterior to the ICRS) cornea demonstrated compressive strains upon IOP increase, and tensile strains upon IOP decrease. ICRS induced an annular shaped tensile strain at its inner border, particularly during IOP increase. The compressive strains close to the tunnel remained with ICRS implantation. Corneal curvature changes were limited to the corneal regions subjected to strain.

Tunnel creation and ICRS implantation induce localized strains in cornea regions that coincide with those of refractive changes[ETN1] [SK2] , suggesting that corneal strain and curvature are directly related. Studying corneal strain in response to surgical intervention may provide new insights on underlying working principles.