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Junhua Tang, Jun Liu; Ultrasonic Measurement of Human Scleral Strains under Physiological Loadings. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2799.
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Scleral mechanical properties may affect the mechanical environment of the optic nerve head. The purpose of this study is to examine human scleral tensile and through-thickness strains under physiological loadings using non-invasive ultrasound speckle tracking.
Eight human globes were tested within 72 hours post mortem. The posterior half of the sclera shell was mounted onto a custom-built pressurization chamber with a saline column connected to control the intraocular pressure (IOP), which was confirmed by a pressure sensor. An ultrasound system (Vevo660, VisualSonics Inc., Toronto) with a 55MHz transducer was employed to acquire B-mode ultrasound images at the posterior pole along both circumferential and meridian directions. IOP was gradually increased from 5 mmHg to 45 mmHg at steps of 2.5 mmHg. The displacement fields were calculated by ultrasound speckle tracking. Both through-thickness compressive strain and tensile strain images were derived from the displacement fields, and the average strain values were calculated within the cross-sectional image (2 mm wide).
A non-invasive ultrasound method was used to examine the tensile and compressive strains through the thickness of human sclera. Our results showed that the compressive strains were substantially larger than the tensile strains. The current study did not detect a significant difference between meridianal and circumferential tensile strains when averaged through-thickness. Future studies will apply the ultrasound method to investigate regional variations of the viscoelastic properties in the corneoscleral shell.
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