Gaze-evoked deformations of the optic nerve head in thyroid eye disease

Purpose To assess gaze evoked deformations of the optic nerve head (ONH) in thyroid eye disease (TED), using computational modelling and optical coherence tomography (OCT). Methods Multiple finite element models were constructed: One model of a healthy eye, and two models mimicking effects of TED; one with proptosis and another with extraocular tissue stiffening. Two additional hypothetical models had extraocular tissue softening or no extraocular tissue at all. Horizontal eye movements were simulated in these models. OCT images of the ONH of 10 healthy volunteers and 1 patient with TED were taken in primary gaze. Additional images were recorded in the same subjects performing eye movements in adduction and abduction. The resulting ONH deformation in the models and human subjects was measured by recording the ‘tilt angle’ (relative antero-posterior deformation of the Bruch’s membrane opening). Effective stress was measured in the peripapillary sclera of the models. Results In our computational models the eyes with proptosis and stiffer extraocular tissue had greater gaze-evoked deformations than the healthy eye model, while the models with softer or no extraocular tissue had lesser deformations, in both adduction and abduction. Scleral stress correlated with the tilt angle measurements. In healthy subjects, the mean tilt angle was 1.46° ± 0.25 in adduction and −0.42° ± 0.12 in abduction. The tilt angle measured in the subject with TED was 5.37° in adduction and −2.21° in abduction. Conclusions Computational modelling and experimental observation suggest that TED can cause increased gaze-evoked deformations of the ONH.