Purchase this article with an account.
Junhua Tang, Richard Hart, Cynthia Roberts, Paul Weber, Xueliang Pan, Jun Liu; Regional variation of scleral strains measured on human whole globes using ultrasound speckle tracking. Invest. Ophthalmol. Vis. Sci. 2013;54(15):54.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Scleral mechanical properties are important in affecting the optic nerve head response to intraocular pressure (IOP) elevations. The purpose of this study is to examine the regional (anterior to posterior) variance of scleral mechanical responses to IOP elevations on whole human globes using non-invasive ultrasound speckle tracking.
Five human globes from 4 donors (age: 62 to 75 yo) were tested within 6 days post mortem. The globes were secured by a thin needle (32G) penetrating through the equator in the superior-inferior direction and another needle (28G) through the central cornea into the anterior chamber. An ultrasound probe (55MHz, Vevo660, Visualsonics) was employed to scan the anterior, equatorial, and posterior sclera in a randomized order. All three regions were on the temporal side of the globe. Two scans (along the meridian direction and the circumferential directions) were taken in each region. Prior to measurements, each globe was subject to preconditioning and allowed for recovery. IOP was then gradually increased from 5 to 15 mmHg at steps of 2.5 mmHg and then 15 to 45 mmHg at steps of 5 mmHg with ultrasound signals being acquired at each step. The displacements and strains were calculated using the algorithm described previously (Tang & Liu, J Biomech Eng 2012, 134(9)).
The average tangential strains were 0.27±0.24 %, 0.54±0.36 %, 0.66±0.39 %, and 0.78±0.43 % in the posterior sclera, 0.18±0.12 %, 0.30±0.19 %, 0.42±0.24 %, and 0.55±0.41 % in the equatorial sclera, and 0.12±0.07%, 0.24±0.09 %, 0.34±0.14 %, and 0.43±0.17 % in the anterior sclera at pressures of 15, 25, 35 and 45 mmHg, respectively. The tangential strains in the posterior sclera were significantly larger than in the anterior sclera at pressures of 20, 25, 30, and 40 mmHg (P’s < 0.05, paired t-tests). No significant difference was found between the tangential strains along the meridian direction and those along the circumferential direction, likely due to the small sample size for this preliminary study.
Scleral mechanical responses to IOP were characterized in human whole globes. Significant regional variations were found in the mechanical response to IOP in human sclera with the posterior having the largest strains at the same IOP elevations. These results could provide useful information for developing biomechanical models of the whole ocular shell.
This PDF is available to Subscribers Only