Altered biomechanical properties are an important precursor for degenerative tissue pathologies. In the eye, diagnostic tools are demanded to be non-invasive, quickly-performed and of high resolution. To meet this need, a novel technique is presented based on an under-pressure chamber applying a homogenous mechanical load on the ocular shell similar to the intraocular pressure, and simultaneous phase-sensitive recording of axial displacements and strain by optical coherence tomography. Results are presented that visualize the instantaneous mechanical effect of patterned corneal cross-linking in ex vivo rat eyes, and the creep response of cornea and crystalline lens in an in vivo subject.
A new vibrography approach based on OCT is suggested for the measurement of corneal oscillations during external harmonic excitation avoiding the need of synchronization and thus making corneal vibrography accessible with standard OCT equipment.
The combination of air-puff systems with real-time corneal imaging (i.e. Optical Coherence Tomography (OCT), or Scheimpflug) is a promising approach to assess the dynamic biomechanical properties of the corneal tissue in vivo. In this study we present an experimental system which, together with finite element modeling, allows measurements of corneal biomechanical properties from corneal deformation imaging, both ex vivo and in vivo. A spectral OCT instrument combined with an air puff from a non-contact tonometer in a non-collinear configuration was used to image the corneal deformation over full corneal cross-sections, as well as to obtain high speed measurements of the temporal deformation of the corneal apex. Quantitative analysis allows direct extraction of several deformation parameters, such as apex indentation across time, maximal indentation depth, temporal symmetry and peak distance at maximal deformation. The potential of the technique is demonstrated and compared to air-puff imaging with Scheimpflug. Measurements ex vivo were performed on 14 freshly enucleated porcine eyes and five human donor eyes. Measurements in vivo were performed on nine human eyes. Corneal deformation was studied as a function of Intraocular Pressure (IOP, 15-45 mmHg), dehydration, changes in corneal rigidity (produced by UV corneal cross-linking, CXL), and different boundary conditions (sclera, ocular muscles). Geometrical deformation parameters were used as input for inverse finite element simulation to retrieve the corneal dynamic elastic and viscoelastic parameters. Temporal and spatial deformation profiles were very sensitive to the IOP. CXL produced a significant reduction of the cornea indentation (1.41x), and a change in the temporal symmetry of the corneal deformation profile (1.65x), indicating a change in the viscoelastic properties with treatment. Combining air-puff with dynamic imaging and finite element modeling allows characterizing the corneal biomechanics in-vivo.
Conference Committee Involvement (2)
Emerging Technologies for Cell and Tissue Characterization
28 June 2023 | Munich, Germany
Emerging Technologies for Cell and Tissue Characterization
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