Assessment of stiffness of posterior eye wall in myopic eyes with an ultrasound-based algorithm using strain elastography

Abstract

Purpose : Myopic progression is commonly caused by axial elongation in an eye resulting in the thinning and reduced stiffness of the sclera. There exist limited studies on the stiffness of the posterior eyewall in myopic eyes. Our goal is to examine whether myopic eyes had greater deformability in the posterior eye of a cohort of adults in Singapore.

Methods : Fifty-eight myopic eyes of 29 subjects (ages 37-87) were enrolled.

Ultrasound (US, Quantel Aviso, 20 MHz) B-mode scans were performed in primary gaze across 100 frames to study the posterior of each eye. Manual compression by a handheld ophthalmodynamometer was used at specified intervals to capture the displacement over time and assess the degree of deformability, or strain, of the tissues of the retina-choroid-sclera (RCS) layer in the posterior eye wall.

For each frame, strain elastography was used to measure the relative stiffness (RS) of several regions of interest (ROI) in RCS layer, with orbital fat as the baseline. Softer tissues experience more strain and are expected to be less stiff than harder tissues.

Results : Average RS across 100 frames was compared across eyes for ROIs in RCS layer. At an interval of before-and-after compression, paired t-test showed significant difference between the change in average RS for a ROI (p=0.01) and across 2 different ROIs (p=0.01 and p<0.01) when compared against the baseline orbital fat. Average RS at 2 different intervals of before-and-after compression showed significant difference for an ROI (p=0.01) and of 2 different ROIs (p=0.01 and p=0.04) for paired t-test.

Axial length (AL, measured by IOLMaster) ranged 22.59 to 30.72 mm and spherical error (SE) ranged from 0.7 to -15.7 D. Increase in AL (per 1 mm) showed a decrease in average RS for an RCS layer ROI during compression of -0.283 (R²=0.40, p<0.01) and no compression of -0.0139 (R²=0.19, p=0.04). During compression, increase in SE (per 1 D) showed an increase in average RS of 0.00783 (R²=0.23, p=0.02) for an RCS layer ROI.

Conclusions : Our qualitative and semiquantitative measure of posterior eye wall strain shows promise as an imaging biomarker identifying regions in myopic eyes that are less stiff and more susceptible to deformability that, when combined with other metrics (AL, SE) may help assess at an early stage, the risk of progression of a stable high myopia eye to PM with staphyloma.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.