Kinematics of the Upper Eyelid and the Globe During Downward Excursion With Comparative Analysis in Patients With Thyroid Eye Disease

Abstract

Purpose: To analyze the kinematics of the upper eyelid and the globe on downward excursion for potential use in monitoring thyroid eye disease (TED) progression in an objective manner.

Methods: Ten normal volunteers and 10 patients with TED were studied. A high-speed (240 fps) digital camera with a coaxial light source set at a constant distance from the subjects' eyes was used to record the excursion of the upper eyelid and the globe from extreme upgaze to extreme downgaze. Clinical data, including age, gender, race, thyroid function tests, Vision, Inflammation/Congestion, Strabismus/motility restriction, Appearance/exposure score (primary surgeons' preference of TED grading system), exophthalmometry, and eyelid measurements were collected for all patients with TED. Frame-by-frame analyses of the videos were performed using Python software (version 3.6) and the Open Source Computer Vision Library. Temporal resolution was obtained by measuring the number of frames from initiation of eyelid and globe movement from extreme upgaze (t 0 ) to extreme downgaze (t f ). Spatial resolution was obtained by measuring the number of pixels the eyelid margin and the globe traversed from t 0 to t f . The data were then plotted on a graph to calculate the velocity of the upper eyelid and the globe during downward excursion.

Results: Velocimetric calculations using high-speed photography suggests that downward excursion of the upper eyelid, and the globe occurs in 2 phases: the acceleration phase and the deceleration phase. Comparative analysis of slow-motion videography demonstrates that patients with TED were found to have attenuation in the early acceleration phase of upper eyelid excursion compared with normal subjects. In patients with TED, the difference in velocity between the eyelid and the globe occurs in the early deceleration phase.

Conclusions: The upper eyelid normally synchronizes intimately with the globe during downward eye movement. Data from this study reveal that attenuation mostly in the early deceleration phase of eyelid movement relative to the globe accounts for the dynamic eyelid lag seen on clinical examination. Further analysis is needed to show if a quantified von Graefe sign can be used as an objective means of monitoring progression in TED.