Purchase this article with an account.
Sunny Kwok, Yanhui Ma, Xueliang Pan, Jun Liu; Regional Rate-Dependent Mechanical Response of the Optic Nerve Head. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6186.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To measure and compare anterior and posterior optic nerve head (ONH) and peripapillary tissue (PPT) mechanical response during inflation tests of different rates.
Inflation tests were performed in six porcine whole globes within 72 hours post-mortem. Extraocular tissues were removed and the optic nerve was trimmed flush with the peripapillary sclera. The globes were secured in a custom-built holder and the holder was immersed in saline. Two 20G needles were inserted into the anterior chamber to control and monitor IOP. Inflation from 5 to 40 mmHg at rates of 0.04, 0.4, 4, and 40 mmHg/sec was performed in each eye with a randomized order. The rates were selected to represent a range of physiologic IOP fluctuations at different time scales (Morris et al, IOVS 2013). Ultrasound B-mode images were collected in the nasal-temporal direction using a 50 MHz probe (Vevo 2100, VisualSonics). An ultrasound speckle tracking algorithm (Tang & Liu, JBME 2012) was used to calculate the displacement field at 2.5 mmHg steps, and least squares estimation yielded regional strains in the ONH and PPT. Paired t-tests were used to analyze differences in radial strains at IOP = 30 mmHg between different inflation rates.
Compressive radial strains (Table 1) in all regions increased nonlinearly as IOP increased (Fig 1). The anterior ONH had significantly larger radial strains than other regions (p's < 0.05). Strain response was not statistically different at three inflation rates (40, 4, and 0.4 mmHg/sec) in all four regions (p’s > 0.05). The strain in the anterior ONH increased significantly at a rate of 0.04 mmHg/sec than at other three rates (p's < 0.05, Fig 1A). Similarly, anterior and posterior PPT had larger radial strains at the 0.04 mmHg/sec rate than other rates (p’s < 0.05). The strain in posterior ONH did not change across all tested rates (Fig 1A, p's > 0.05).
The anterior ONH was subject to significantly higher strain at all IOP fluctuation rates, suggesting a higher vulnerability to pressure insult in this region. Our results also suggest that fast IOP fluctuations at rates greater than 0.4 mmHg/sec could still create substantial strains in the anterior ONH (>4%) despite a smaller magnitude than quasi-static (chronic) IOP elevation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Table 1: Radial strains at IOP = 30 mmHg
Figure 1: (A) Radial strain of different regions and (B) strain maps of a representative eye at different inflation rates
This PDF is available to Subscribers Only