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実験的検証モデルを用いたヒト眼球損傷過程に関す る数値解析
アリレザ, キャリミ
https://doi.org/10.15017/1807025
出版情報：Kyushu University, 2016, 博士（工学）, 課程博士 バージョン：
権利関係：Fulltext available.
氏 名 ：アリレザ キャリミ
（様式２）論 文 名 ：Computational analysis for the human eye injury using an experimentally verified anatomical-based model
(
実験的検証モデルを用いたヒト眼球損傷過程に関する数値解析） 区 分 ：甲
論 文 内 容 の 要 旨
Injuries to the eye are accompanied with a harsh over-pressure to its components which are difficult to be diagnosed by ophthalmologists. Numerical models, such as Finite Element (FE), would be applicable for understanding the injury process in each eye component under various loading conditions. The objective of this study was to propose a suitable anatomical-based eye model for injury investigation to all components of the eye. In addition, since understanding the process of injuries to the eye, especially the anterior part, such as the blunt trauma, or in the posterior part, such as the Optic Nerve Head (ONH) injury as a result of increasing the IntraOcular Pressure (IOP), are difficult or almost impossible to be studied experimentally, this study was aimed at analyzing the injury to the anterior and posterior components of the eye using an anatomical-based model. However, in order to have a suitable as well as a reliable eye model, the mechanical properties of the eye components and the experimental validation of the model are deemed important. The mechanical properties of the sclera, owing to its essential role in load bearing during mechanical deformation of the eye as well as the ONH injury in the posterior side of the eye, were separately investigated. The sclera is the most outer component of the eye which retains the intra components of the eye. The optic nerve is the most posterior component of the eye which transfers the signal of vision into the brain for interpretation. The attachment site of the optic nerve to the sclera named as the ONH. The mechanical properties of the sclera were incorporated into our anatomical-based eye model, and then experimentally and numerically verified via the penetration test. A well verified anatomical-based eye model can be employed in various types of injury simulations when the experimental studies in this regard are not available. To show the applications of the model, especially for the anterior and posterior parts, the injuries to the eye components as a consequence of tennis ball impact as well as IOP alteration were analyzed.
In chapter 1, the anatomy of the eye in brief was provided. Comparative analyses on the eye models were carried out and the pros and cons of each of which was discussed. The anatomical-based eye model was established.
The mechanical properties of the sclera were assigned to our anatomical-based eye model, and then experimentally and numerically verified under five different loading rates using penetrating test. Finally, the injury to the anterior and posterior components of the eye were analyzed.
In chapter 2, the mechanical properties of the sclera were experimentally measured in order to be incorporated into our eye model. Due to the crucial role of sclera’s mechanical properties in the ONH injury as well as a wide range of sclera’s elastic modulus, it was decided to experimentally measure the mechanical behavior of this tissue under various loading rates. Since the eye globe during the injury subjects to the mechanical deformation under various rates, having the mechanical properties of the sclera at various rates of loading enabled us to employ a better model as a function of applied load. In addition, such data can be used in other types of injury simulation to the eye. To measure the properties, the fresh dissected sclera tissues were subjected to the series of loadings and its resulted stress-strain as well as stress-relaxation data were interpreted thru the linear elastic, nonlinear hyperelastic, and linear viscoelastic material models. The results showed the elastic modulus range of 1.10-2.92 MPa.
In chapter 3, using the CT/MRI/literature data, an anatomical-based computational model of the eye was established (Fig. 1). The attachment sites of the muscle and the head of the optic nerve into the sclera in this figure were magnified. The eye model was then verified via the set of penetrating experimental tests under five different loading rates up to 1 mm deformation in the apex of the cornea. In order to show the advantage of our eye model compared to the other ones, three eye models were established. The first two models, namely the 1st and the 2nd, were considered as the simple models since the 1st model was considered the eye as a unique component with simple linear elastic behavior.
Similarly, the 2nd model was made of the main eye parts, such as the cornea, lens, sclera, and vitreous body. Other two
models were anatomical-based eye models, and particularly, in our model the iris and the aqueous body at the anterior side were considered separately (Fig. 1). After subjecting these eye models to the same loading condition as that of the experimental penetrating one, the results revealed that our model due to considering all the components of the eye has the most suitable agreement with the experimental stress-strain data in contrast to the simple models, i.e., 1st and 2nd models. When the iris and the aqueous body both were considered as the same solid component (3rd model) despite the anatomical-based model (our model), the small difference from that of the experimental data was observed. At the same amount of displacement, the 3rd model showed lower stress values, and up to 1 mm deformation in the cornea, the stress of this model was 17 kPa whereas the experimental results showed the stress of 50 kPa at the highest strain rate. On the other hand, our anatomical-based model displayed the stress of 50 kPa which shows a very good agreement with the experimental data. The 1st and 2nd models also revealed the stresses of 100 and 270 kPa, respectively, which are way out of the range of the experimental data. In this chapter we could show the advantage of our anatomical-based eye model to compute the amount of stresses and deformations as a consequence of blunt trauma impact compared to the experimental data.
Fig.1. Our proposed anatomical-based eye model.
In chapter 4, since up to now we could propose a well verified eye model which is enriched with the real mechanical properties of the sclera/optic nerve, it was decided to simulate injury to the anterior and posterior sides of the eye as a result of tennis ball impact as well as IOP alteration. Since it has been reported that the blunt trauma impact and IOP alteration can significantly affect the visual acuity by changing the shape of the cornea and lens in the anterior side as well the ONH biomechanics in the posterior side of the eye, using our eye model the amount of stresses and deformations in all the components of the eye were precisely investigated. For the blunt trauma impact, a tennis ball at the speed of 69.29 m/s was hit the eye and for the posterior injury investigation, three different IOP values, i.e., 10, 20, 30 mmHg, were applied on the components which are in direct contact with the aqueous body. The analyses have performed using two different elastic modulus for the sclera/optic nerve, as the reference data (5.50 MPa) and our experimental data (1.65 MPa). The highest stress as a result of tennis ball impact was observed in the cornea at both elastic moduli. The stress in the sclera, retina, and optic nerve were affected by alteration of the elastic modulus while the rest of the components have not been changed. In addition, the results at the IOP of 30 mmHg revealed the radius of curvature of 7.89 and 2.5 mm for the cornea and lens, respectively. The results in this regard were completely in agreement with the clinical data. Since a considerable deformation was observed in the ONH site, the role of the sclera/optic nerve elastic modulus in the deformation and stress of the ONH site was separately investigated in detail.
The results in this regard disclosed the deformations of 10.42 and 16.02 µm at the elastic modulus of 5.50 and 1.65 MPa, respectively, resulting that the deformation of sclera in our anatomical-based model and our experimental material property of sclera was closer to the clinical data.
In chapter 5, the main findings of this study were summarized and highlighted. In addition, some points for the future works were also provided.
