Kunya Zhang

Three-Dimensional Reconstruction and Finite Element Modeling Analysis of the Rabbit Optic Nerve Head in Acute High Intraocular Pressure

To construct a three-dimensional (3D) rabbit optic nerve head (ONH) model by optical coherence tomography (OCT) images, demonstrate the effectiveness and validity of the model by comparison with changes in the ONH in vivo acute high intraocular pressure (IOP) of the living rabbit. Stress and deformation field analysis of the 3D rabbit ONH model was performed using the finite element method (FEM). Immediately after saline was perfused into the anterior chamber of the rabbit eye in an acute high IOP experiment, the same rabbit eye was scanned by OCT, the OCT had a scan speed of 27000 A scans per second with 3.0×3.0×2.3 mm3 (horizontal × vertical × axial) range. The changes of the in vivo ONH in OCT images were compared with the results of the FEM analysis, the morphological deformations were in accordance with the tendency predicted using FEM analysis.

Experimental system for analyzing biomechanical properties of iris tissue based on stereo vision

We designed an experimental system based on stereo vision in order to analyze quantificational biomechanical properties of iris tissue without destroying the structure and function of iris in this paper. This experimental system, which was designed and improved upon the primary experimental device, consists of three vidicons assembled with tripod, a circular desk scaled from one degree to 360 degrees, a signal generator, a special lamp-house, a pupil-blocking simulating device, a negative pressure device, a constant temperature trough assembled with a fixed bracket, a load-pressure trough and a small electric elevator. The new experimental system could simulate the pupil-blocking phenomena. The animal research was proved that the results were consistent with the clinical observation. The new experimental system could also obtain continuous pressure data and corresponding 2D image of iris from three different degrees in the course of load-pressure. The experimental system not only is an ideal experimental system to measure biomechanical properties of iris tissue and pupil-blocking force quantitatively, but also can be used to research small distortion characteristic of other biologic material.

Three-dimensional Hessian matrix-based quantitative vascular imaging of rat iris with optical-resolution photoacoustic microscopy in vivo

Abstract. For the diagnosis and evaluation of ophthalmic diseases, imaging and quantitative characterization of vasculature in the iris are very important. The recently developed photoacoustic imaging, which is ultrasensitive in imaging endogenous hemoglobin molecules, provides a highly efficient label-free method for imaging blood vasculature in the iris. However, the development of advanced vascular quantification algorithms is still needed to enable accurate characterization of the underlying vasculature. We have developed a vascular information quantification algorithm by adopting a three-dimensional (3-D) Hessian matrix and applied for processing iris vasculature images obtained with a custom-built optical-resolution photoacoustic imaging system (OR-PAM). For the first time, we demonstrate in vivo 3-D vascular structures of a rat iris with a the label-free imaging method and also accurately extract quantitative vascular information, such as vessel diameter, vascular density, and vascular tortuosity. Our results indicate that the developed algorithm is capable of quantifying the vasculature in the 3-D photoacoustic images of the iris in-vivo, thus enhancing the diagnostic capability of the OR-PAM system for vascular-related ophthalmic diseases in vivo.

EFFECT OF MECHANICAL PROPERTIES OF THE SUBSTRATE TISSUES ON THE DETERMINATION OF ELASTIC MODULUS OF THE SCLERA USING INDENTATION TEST

The sclera is an important connective tissue that protects the sensitive layers within the eyeball. Identifying the mechanical properties of the sclera near the posterior pole is necessary to analyze the deformation of the sclera and stresses changing in the optic nerve head tissues. We propose a method to determine the mechanical properties of the sclera using dimensional analysis, finite element method and the indentation test. The elastic moduli of the sclera for different indentation depths and positions were identified. We found that the elastic moduli of the sclera varied with indentation depth. This was due to the effect of the mechanical properties of the substrate tissues inside the sclera. The elastic modulus of the choroid had the biggest effect on the determination elastic modulus of the sclera, whereas that of the vitreous body could be ignored when the ratio of the indentation depth to the thickness of the sclera was less than 0.5. The effects of mechanical properties of the substrate tissues become more pronounced at greater indentation depths.

Method to Determine Nonlinear Mechanical Properties Based on the Blood Vessel Inflation Experiment

Objective: To determine the nonlinear mechanical properties of blood vessel. Methods: The deformation information of in vitro blood vessel was obtained when the loadpressure increases gradually from 0 Pa to 300 mmHg using the self-designed device, which includes the image capturing part and the loading part. Then the radial deformations of blood vessel in different load pressure were computed using the method of the image processing. The constitutive relationship is taken as an exponential expression proposed by Fung. Results: The nonlinear parameters can obtain using the method of the curve fitting. This method can be used to determine the nonlinear mechanical properties of the blood vessel.

An Inverse Approach to Determine the Elastic Modulus of Bone Tissue by the Indentation Tests

Recently, based on the finite element method and dimensional analysis, we proposed an inverse approach to determine the elastic modulus of power-law engineering materials by using indentation tests. In this study, we make an attempt to apply the method developed to some elastoplastcic biological materials, such as bone tissue, which do not exhibit power-law behaviour. The elastic modulus of sheep vertebra and several bones of adult are identified. It is found that the relative errors of the identified elastic modulus are very small. It is proved that the inverse approach developed for power-law materials can be applied to identify elastic modulus of bone tissue.

Research on the Relationship between Angle Closure and Morphological Changes in Iris Based on the Animal Experiment Simulating Pupillary Block

Objective: To explore the mechanism of the phenomenon of Primary Angle Closure Glaucoma’s (PACG) blocking of the iris-cornea angle and to predict the development of PACG in the future. Material and Methods: Based on the biomechanical experiment of the whole iris and inducted parameter β, the mechanical balanceable equation was established. Simulating the relationship as follows: the differential pressure between the anterior and posterior chambers (P) and the contour of the iris, the P and the iris-cornea angle, the more anterior lens position and the iris-cornea angle, etc. Results: The curve of the iris-cornea angle and P is exponential rule. The increase of P is a very important factor of the blocking of the iris-cornea angle. The relation between the more anterior lens position and the convex shape of iris is plus correlation but the more anterior lens position and the change of iris-cornea angle is negative correlation.