Collagen crosslinking and degradation have been associated with changes in tissue stiffness. Although femtosecond laser irradiation might induce either collagen crosslinking or collagen degradation, the photomodulation effects are still unclear. Our goal was to characterize effects of photomodulation. We found that collagen crosslinking and degradation were related to the number of treatments, and photomodulation-involved reactants diffuse. The precision of photomodulation was at the micrometer level in both lateral and axial directions. Polarized light microscopy shows no change in collagen architecture in the treatment boundary and without the production of damaging thermoacoustic effects.
We characterized the stiffness and anisotropy of the equatorial sclera and its dependence on intraocular pressure (IOP). Porcine eyes were tested using ultrasound elastography under IOP control. Shear waves were induced using a mechanical shaker, and an off-axis 17.8 MHz transducer used to track the wave propagation in the equatorial and anterior-posterior directions. Wave speed was measured and used to estimate directional Young’s moduli. Anisotropy was defined as the ratio of the equatorial moduli to the anterior-posterior moduli. Sclera was stiffer in the equatorial direction, with anisotropy decreasing with IOP, from, 5.1 at 10 mmHg to 3.7 at 30 mmHg.
Most soft tissues, such as cornea and sclera, exhibit mechanical anisotropy. Obtaining the anisotropy properties of the sclera can be helpful in understanding the mechanical properties of the eyes in the development and progression of glaucoma and myopia. In this work, we have demonstrated a method of quantifying the anisotropic Young’s modulus values for sclera, using a confocal Lamb wave based acoustic radiation force optical coherence elastography (ARF-OCE). We have measured mechanical anisotropy in porcine sclera by measuring the Young’s modulus along both the equator direction and anterior to posterior direction. The results demonstrate the Young’s modus in the equator direction is 15-30% higher than that in the anterior to posterior direction.
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