CORNEAL STRAIN INDUCED BY INTRASTROMAL RING SEGMENT IMPLANTATION VISUALIZED WITH THE NOVEL OPTICAL COHERENCE ELASTOGRAPHY

Recently, we reported a novel technique to visualize corneal strain based on optical coherence tomography (OCT) imaging and small-amplitude IOP modulation that permits an evaluation of corneal biomechanics in a condition very close to the eye’s natural state. In order to better understand the underlying mechanisms of the ICRS-induced refractive change, it is fundamental to quantify the stress and strain fields provoked by ICRS implantation. Therefore, the purpose of the present study is to record the axial strain field in the cornea directly after creating a stromal tunnel and implanting an intracorneal ring segment (ICRS).

Freshly enucleated porcine eyes were obtained and assigned either to ICRS implantation, tunnel creation only or virgin control. Immediately after manual tunnel creation and ICRS positioning, the entire eye globe was mounted on 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 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 on 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 after ICRS implantation. Corneal curvature changes were concentrated on regions where strain was induced.

For the first time it was possible to obtain strain maps of the corneas after ICRS implantation using optical coherence elastography. ICRS implantation induces localized strains in the regions subjected to refractive changes, 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.