Biomechanics of the Human Optic Chiasmal Compression Xiaofei Wang A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Engineering and Information Technology The University of New South Wales August 2014 PLEASE TYPE THE .UNIVERSITY OF NEW SOUTH WAl.,,~S Thesis/Dissertation Sheet Surname or Family name: Wang First name: Xiaofei Other name/s: Abbreviation for degree as given in the University calendar: PhD School: Engineering and Information Technology Faculty: UNSW Canberra at ADFA Title: Biomechanics of the human optic chiasmal compression Abstract 350 words maximum: (PLEASE TYPE) Bitemporal hemianopia is a type of partial visual field defect in which vision is impaired in the temporal halves of the visual fields of both eyes. Bitemporal hemianopia has many known causes but the most common cause is the chiasmal compression caused by a pitu itary tumour. However, the precise mechanism of bitemporal hemianopia is still not clear. This thesis aims to explore the possible causes of bitemporal hemianopia by investigating the biomechanics of chiasmal compression. · · Simple optic chiasmal compression models and nerve fibre models were developed first, using finite element modelling, for analysis of the mechanical behaviours of the chiasm. An ilndividual-specific optic ch iasmal compression model was then built to account for more accurate geometry and material properties of the chiasm. Multi-scale analyses were then performed to examine the micro-scale interactions of the nerve fibres using representative .volume elements. To further improve the fidelity of the model, the detailed nerve fibre arrangements in the optic chiasm were investigated using photomicrographic image analysis of the human chiasmal slices. Finally, an ex viva experiment of optic ch iasmal compression was conducted for further validation of the numerical method. Strain distributions in the optic chiasm and optic nerve fibres were obtained from the numerical models. The results of the chiasmal model broadly agreed with the limited experimental results in the literature, ind icating that the fin ite element modelling can be a useful tool for analysing chiasmal compression. Simulation results showed that, under the same loading conditions, the strain distri bution in crossed nerve fibres was much more nonuniform and locally higher than in uncrossed nerve fibres. This strain difference may account for the phenomenon of bitemporal hemianopia. The nerve fibre arrangement study added more details to the present understanding of fibre trajectories in the optic chiasm. The FEM model simulated the ex viva experi ment reasonably well which further underlines the usefulness of FEM in investigating the ch iasmal compression . Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South W ales or its agents the right to archive and to make available my thesis or dissertaiion in whole or in part in the University libraries in all forms of media, now or here after known , subject to the provisions of the Copyright Act 1968. I retain all property rights , such as patent rights. I also retain the right to use in future works (such as articles or books) all or pa rt of this thesis or dissertation. I also authorise University Microfi lms to u_se the 350 word abstract of my thesis in Dissertation Abstrads International (this is applicable to doctora l theses only). ~~ -- ~ · · · ·· ··· ·· ··· · · · · ·· ; ......... ..JE /A .1/ Zo.l4.. Signature Date · ·· ······~····· · · · The University recognises th at there may be exceptional circumstances requiring restrictions on copyin g or-conditions on use. Requests fo r restriction for a period of up to 2 years must be made in writing. Requests for a longer pericid of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS ORIGINALITY STATEMENT 'I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of thi s thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation a mguistic expression is acknowledged.' Signed Date 1~ / .~ .. ...... .~ ..7/ . ... ...' .'f .. ........ ...... ..... COPYRIGHT STATEMENT 'I hereby grant the University of New South Wales or its agents the right ,Jo· archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertatio Signed 1 Date .. !± .................. ... .. ...... ..... 71.i !. .~ ........~ . .. .. AUTHENTICITY STATEMENT 'I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any~ minor variations in formatting, they are the result of the :~:~:~io~todigttal .·· ·· ·············· ·· ··········· J-7/11 Date ···· ··· ······· ·· ·· ·· ·· ··· ···· /01~... ... ... ... ... ... ........... ..... .... ...... ... Acknowledgements I would like to thank my supervisor Associate Professor Andrew Neely for giving me the opportunity to do my PhD thesis. This thesis would have not been possible without his continuous support, patience, encouragement and immense knowledge. He is not only a supervisor but also a friend. I would also like to thank my co-supervisor Professor Christian Lueck in the Canberra Hospital and the Australian National University, for his tremendous support and guidance. He always provides detailed and valuable feedback quickly. I am very grateful for having a chance to work with him. I would like to thank my colleagues Neeranjali Jain and Swaranjali Jain, for their extremely useful inputs to this project. I would also like to thank the following people for their involvement in this project and helpful discussions: Gawn McIlwaine, Dr Murat Tahtali, Thomas Lillicrap and Professor Sanjiv Jain. It’s an honour to work with so many smart people. I would like to thank all my friends and colleagues in Canberra for making my time here enjoyable and memorable. Most of all, I would like to thank Jinge Luo, Yafei Wang, Yali Wang and my parents for their constant support and encouragement. ii Publications Arising from this Thesis Journal Articles 1. Wang X, Neely A, McIlwaine G and Lueck C. Multi-scale analysis of optic chiasmal compression by finite element modelling. Journal of Biomechanics. 47 (10), pp. 2292-2299. 2. Wang X, Neely A, McIlwaine G, Tahtali M, Lillicrap T and Lueck C. Finite element modelling of optic chiasmal compression. Journal of Neuro- Ophthalmology. (In press) published online, DOI: 10.1097/WNO.0000000000000145 3. Jain N, Jain S, Wang X, Neely A, Tahtali M, Jain S and Lueck C. Visualisation of nerve fibre orientations in the human optic chiasm using photomicrographic image analysis. (Prepare to submit to Journal of Anatomy) 4. Wang X, Neely A, Jain N, Jain S, Tahtali M, Jain S and Lueck C. Biomechanics of the human optic chiasmal compression. (Prepare to submit to Investigative Ophthalmology & Visual Science) Refereed Conference Papers 1. Wang X, Neely A, Lueck C, Tahtali M, McIlwaine G and Lillicrap T. Parametric studies of optic chiasmal compression biomechanics using finite element modelling, 7th Australasian Congress on Applied Mechanics, ACAM 7 9-12 December 2012, Adelaide, Australia. 2. Wang X, Neely A, McIlwaine G and Lueck C. Biomechanics of chiasmal compression: sensitivity of the mechanical behaviours of nerve fibres to variations in material property and geometry. 11th World Congress on Computational Mechanics, 20-25 July 2014, Barcelona, Spain. Conference Abstracts and Poster Presentations 1. McIlwaine G, Wang X, Neely A, Tahtali M, Lueck C. Why does chiasmal compression cause bitemporal hemianopia? The Oxford Ophthalmological Conference, Oxford, UK, 1-4 July, 2012 2. Lueck C, Wang X, Neely A, Tahtali M, McIlwaine G, Lillicrap T. Finite element modelling of chiasmal compression: nearer to an understanding of iii bitemporal hemianopia? The 39th Meeting of the North American Neuro- Ophthalmology Society, Snowbird, UT, USA, 9-14 February, 2013. 3. Lueck C, Wang X, Neely A, Tahtali M, Lillicrap T, McIlwaine G (2013). Finite Element Modelling of Chiasmal