Gaze Evoked Deformations of the Optic Nerve Head in Thyroid Eye Disease

Abstract

Purpose : To assess the effect of optic nerve traction (during eye movements) on optic nerve head (ONH) deformations in subjects with thyroid eye disease (TED), using optical coherence tomography (OCT) and computational modelling.

Methods : OCT images of the ONH of 10 healthy volunteers (n = 20) and 1 patient with unilateral ocular thyroid symptoms (n = 1) were taken in primary gaze. Additional images were captured with subjects performing horizontal eye rotations of 20 degrees in adduction and abduction. The resulting ONH deformation (shear) was measured by registering the central B-scans at the Bruch’s membrane (BM) opening, then recording angular displacement of the peripapillary BM on both the nasal and temporal sides of the scleral canal (Figure). To interpret our clinical observations, two finite element models were built:
One finite-element model of the orbit was used to approximate a healthy eye. A modified eye model was also created to mimic the effects of TED. Horizontal eye movements were simulated in order to compare model deformations with those observed experimentally.

Results : In our experimental observations of healthy eyes, angular displacement of the BM was greater on the nasal side of the scleral canal than the temporal side in both adduction and abduction. Deformation of both sides was greater in adduction than abduction. These patterns were also observed in the TED eye. For this eye, deformations were larger than those in the set of healthy eyes.
In the model of the normal eye, deformation in the BM was similar in both adduction and abduction. In the model of the thyroid-affected eye, the pattern of deformation agreed with OCT in abduction but not adduction. Simulated eye movement in the TED eye caused elevated stress concentration in the peripapillary sclera.

Conclusions : Our preliminary results suggest that proptosis or orbital congestion caused by Graves’ disease may exacerbate the mechanical effects of eye movement at the optic nerve head. This may explain some cases of dysthyroid optic neuropathy. More patient data is needed to account for variation in the nature and severity of tissue changes that accompany TED.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

A: Healthy ONH in primary gaze. B: The same ONH in 20 degrees of abduction. C: Overlay of A and B illustrating relative tissue displacement. D-F: Corresponding images for an eye with signs of thyroid eye disease. G: Angular displacement of the Bruch’s membrane.