Finite Element Modeling of Chiasmal Compression

Simon Trevor Thomas

Abstract


It is widely agreed that compression of the optic chiasm by an external pressure causes a visual defect known as bitemporal hemianopia. However, disagreement arises over the mechanism by which this external pressure causes only crossing, nasal nerve fibres within the optic chiasm to be affected, whilst leaving temporal, uncrossed fibres predominantly unaffected. It has recently been proposed that the primary reason for this selective targeting of nasal nerve fibres is due to their crossing geometry amplifying the local pressure experienced by the fibres. This thesis project has extended previous work with the use of Finite Element Analysis (FEA) to model the stress distribution produced in the optic chiasm, when displaced by an abnormal growth in the pituitary gland. Results have shown that in the case of a pre- or post-fixed optic chiasm the region of highest stress produced sits evenly across nasal and temporal nerves. Thus indicating that the location of the crossing nasal nerves within the optic chiasm can not always be the reason for their being selectively targeted, and therefore some other mechanism must be responsible. Investigation has been conducted into the validity of the material properties used in the FEA and into improving the geometric accuracy of the models through the use of data from magnetic resonance images.

Keywords


Bitemporal Hemianopia, Optic Chiasm, FEA

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