Ultrasonic Assessment of Gaze-Induced Deformation of Posterior Staphyloma in Highly Myopic Eyes by Means of a Semi-Automated Assessment of Local Radius of Curvature

Abstract

Purpose : Ultrasound is a commonly available tool to assess the properties of the posterior eye, allowing us to characterize morphological changes and mechanical properties with kinetic exam. Here, we determine if the stress and strain of eye movements result in gaze-induced deformation of posterior staphyloma in highly myopic (HM) eyes.

Methods : A prospective imaging study was performed on 101 HM eyes (axial length range: 27.0 to 39.3 mm) of 52 patients with a clinical diagnosis of posterior staphyloma. 10 MHz B-scan ultrasound images oriented along the visual axis were acquired while subjects fixated in 5 directions (primary, nasal, temporal, down and up gaze). An algorithm was used to assess the local radius of curvature (K in mm^-1). Specifically, an intensity-based segmentation algorithm tracked the vitreoretinal boundary and calculated K using differential calculus applied to the traced boundary. Positive K implies anterior convexity, whereas negative K implies posterior convexity. Larger K value implies a greater spatial change. The standard deviation (std) of K represents the level of non-uniformity along the curve of the entire posterior wall. One static frame for each scan direction was chosen to calculate the average and std of K in each direction. The Kruskal-Wallis test with the Tukey-Kramer method (as post hoc multiple comparisons) was performed to assess statistical significance between groups.

Results : Overall, we found significant gaze-induced posterior eye shape changes among the different gazes when grouped together (p < 0.001). Specifically, among the vertical scans, the average K in upgaze was 0.019 mm^-1 greater than in primary gaze (p < 0.001). Also, the average K in upgaze was 0.021 mm^-1 greater than in downgaze (p < 0.001). Std of K in upgaze was 0.081 mm^-1 greater than in primary gaze (p < 0.001). Also, std of K in upgaze was 0.058 mm^-1 greater than in downgaze (p < 0.001). There were no significant gaze-induced posterior eye shape changes with horizontal eye movements (all p > 0.05).

Conclusions : Significant gaze-induced staphyloma deformation was confirmed by ultrasound B-scan-based assessment, which is consistent with studies suggesting the association of environmental factors, such as excessive nearwork, with myopia development and progression.

This is a 2021 ARVO Annual Meeting abstract.