3-D assessment of gaze-induced eye shape deformations and downgaze-induced vitreous chamber volume increase in highly myopic eyes with staphyloma.

PURPOSE: To determine if the stress of normal eye movements results in gaze-induced globe deformations, vitreous chamber axial length and vitreous chamber axial volume (VCAV) change in highly myopic eyes.
METHODS: A prospective imaging study was performed on 82 eyes of 43 patients with high myopia (>27 mm of axial length) with a clinical diagnosis of staphyloma. Three-dimensional MRI scans were acquired while subjects gazed in five directions (primary, nasal, temporal, superior and inferior). Surface renderings were generated, and a processing pipeline was created to automate alignment of the eye and to measure VCAV within 5.5 mm of the visual axis for each eye in every gaze. The degree of gaze-induced globe deformation was determined by calculating the Dice coefficient to assess the degree of overlap of the sclera at each eccentric gaze with that found in primary gaze. Each eccentric gaze VCAV was compared to VCAV in primary gaze using a fixed-effects regression allowing for subject-specific and eye-specific effects.
RESULTS: The Dice coefficient showed significant gaze-induced eye shape changes in all gazes (all p<0.0001). There were no statistically significant gaze-induced VCAV changes when comparing primary gaze to nasal, temporal or upgaze. However, when changing from primary to downgaze, VCAV was increased by +4.79 mm3 (p=0.002, 95% CI 1.71 to 7.86).
CONCLUSION: Significant gaze-induced globe deformation was noted in all gazes, but a reversible, instantaneous VCAV increase occurred only in downgaze, which is consistent with studies supporting the association of environmental factors such as near work with myopia development and progression. © Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.