Understanding the mechanical properties of the iris can help to have an insight into the eye diseases with abnormalities of the iris morphology. Material parameters of the iris were simply calculated relying on the ex vivo experiment. However, the mechanical response of the iris in vivo is different from that ex vivo, therefore, a method was put forward to determine the material parameters of the iris using the optimization method in combination with the finite element method based on the in vivo experiment. Ocular hypertension was induced by rapid perfusion to the anterior chamber, during perfusion intraocular pressures in the anterior and posterior chamber were record by sensors, images of the anterior segment were captured by the ultrasonic system. The displacement of the characteristic points on the surface of the iris was calculated. A finite element model of the anterior chamber was developed using the ultrasonic image before perfusion, the multi-island genetic algorithm was employed to determine the material parameters of the iris by minimizing the difference between the finite element simulation and the experimental measurements. Material parameters of the iris in vivo were identified as the iris was taken as a nearly incompressible second-order Ogden solid. Values of the parameters μ ₁, α ₁, μ ₂ and α ₂ were 0.0861 ± 0.0080 MPa, 54.2546 ± 12.7180, 0.0754 ± 0.0200 MPa, and 48.0716 ± 15.7796 respectively. The stability of the inverse finite element method was verified, the sensitivity of the model parameters was investigated. Material properties of the iris in vivo could be determined using the multi-island genetic algorithm coupled with the finite element method based on the experiment.

The vitreous body keeps the lens and retina in place and protects these tissues from physical insults. Existing studies have reported that the mechanical properties of vitreous body varied after liquefaction, suggesting mechanical properties could be effective parameters to identify vitreous liquefaction process. Thus, in this work, we aimed to propose a method to determine the mechanical properties of vitreous bodies. Fresh porcine eyes were divided into three groups, including the untreated group, the 24 h liquefaction group and the 48 h liquefaction group, which was injected collagenase and then kept for 24 h or 48 h. The indentation tests were carried out on the vitreous body in its natural location while the posterior segment of the eye was fixed in the container. A finite element model of a specimen undertaking indentation was constructed to simulate the indentation test with surface tension of vitreous body considered. Using the inverse method, the mechanical parameters of the vitreous body and the surface tension coefficient were determined. For the same parameter, values were highest in the untreated group, followed by the 24 h liquefaction group and the lowest in the 48 h liquefaction group. For C₁₀ in the neo-Hookean model, the significant differences were found between the untreated group and liquefaction groups. This work quantified vitreous body mechanical properties successfully using inverse method, which provides a new method for identifying vitreous liquefactions related studies.

Glaucoma is a trans-synaptic neurodegenerative disease, and the pathological increase in intraocular pressure (IOP) is a major risk factor of glaucoma. High IOP alters microstructure and morphologies of the brain tissue. Since mechanical properties of the brain are sensitive to the alteration of the tissue microstructure, we investigate how varying durations of chronic elevated IOP alter brain mechanical properties. A chronic high IOP rat model was induced by episcleral vein cauterization with subconjunctival injection of 5-Fluorouracil. At 2, 4 and 8 weeks after induction, indentation tests were performed on the brain slices to measure mechanical properties in the hippocampus, lateral geniculate nucleus and occipital lobe of both hemispheres. Meanwhile, the brain’s microstructure was assessed via F-actin and myelin staining. Compared to the blank control group, the Young’s modulus decreased in all three brain regions in the highIOP experimental groups. F-actin fluorescence intensity and myelin area fraction were reduced in the hippocampus, while β-amyloid levels and tau phosphorylation were elevated in the experimental groups. Our study provides insight into Alzheimer’s disease pathogenesis by demonstrating how chronic high IOP alters the brain’s mechanical properties.