July 2019
Volume 60, Issue 9
Free
ARVO Annual Meeting Abstract  |   July 2019
Regional Rate-Dependent Mechanical Response of the Optic Nerve Head
Author Affiliations & Notes
  • Sunny Kwok
    Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
  • Yanhui Ma
    Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
  • Xueliang Pan
    Department of Bioinformatics, The Ohio State University, Ohio, United States
  • Jun Liu
    Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
    Department of Ophthalmology and Visual Science, The Ohio State University, Ohio, United States
  • Footnotes
    Commercial Relationships   Sunny Kwok, None; Yanhui Ma, None; Xueliang Pan, None; Jun Liu, None
  • Footnotes
    Support  NIH RO1EY020929 and NIH RO1EY025358
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 6186. doi:
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    • Get Citation

      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.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : To measure and compare anterior and posterior optic nerve head (ONH) and peripapillary tissue (PPT) mechanical response during inflation tests of different rates.

Methods : 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.

Results : 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).

Conclusions : 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

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

Figure 1: (A) Radial strain of different regions and (B) strain maps of a representative eye at different inflation rates

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