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  • Thyroid Eye Disease and Gaze-Evoked ONH Deformations

    By Lynda Seminara
    Selected by Prem S. Subramanian, MD, PhD
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    Journal Highlights

    British Journal of Ophthalmology
    Published online Jan. 19, 2021

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    Fisher et al. questioned whether gaze-evoked deformations of the optic nerve head (ONH) are, in turn, aggravated by thyroid eye disease (TED). Based on their computational models and OCT images, TED appeared to amplify these distortions. The authors emphasized that larger studies would be needed to confirm the findings.

    For this exploration, the authors built three finite-element models (one healthy eye, one eye with proptosis, one eye with extraocular tissue stiffening) and two hypothetical models (softening and lack of extraocular tissue). Horizontal eye movements were simulated in the orbits, and each deformation of the ONH was evaluated. For verification, OCT images of the ONH were obtained from 10 healthy volunteers and a patient with TED while the participants’ eyes were in primary gaze, adduction, and abduction.

    The effects of TED on ONH mechanics were assessed by measuring the tilt angle (i.e., relative anteroposterior displacement of Bruch membrane opening) in the models and the human participants. Negative tilt angles indicated that the nasal side of the opening moved posteriorly relative to the temporal side, and vice versa.

    The authors found that gaze-evoked deformations were greater in eyes with proptosis and with stiffer extraocular tissue than in the healthy eye. In contrast, deformations were less pronounced in the models with soft or no extraocular tissue, in both adduction and abduction. The mean tilt angle for healthy volunteers was 1.46 ± 0.25 degrees in adduction and −0.42 ± 0.12 degrees in abduction. The volunteer with TED had the largest tilt angles: 5.37 degrees in adduction and −2.21 degrees in abduction.

    Although gaze-evoked ONH deformations often are ascribed to optic nerve traction, the authors suggested that the distortions observed in their finite-element models may relate to the presence and stiffness of orbital fat. Moreover, fat obstruction may explain why ONH deformations were more severe in the patient with TED than in healthy eyes, they said. To validate these findings, they recommended exploring gaze-evoked deformations in a large series of patients with TED.

    The original article can be found here.