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Ultrasound Speckle Tracking Methods to Study the Biomechanical Factors of Ocular Disease

Pavlatos, Elias
http://orcid.org/0000-0002-9341-1284
http://rave.ohiolink.edu/etdc/view?acc_num=osu1532039603048926

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Biomedical Engineering.
The biomechanical behavior of the eye is critical to the maintenance of ocular health and is yet to be fully understood. The primary load-bearing structures of the eye are the cornea, sclera, and optic nerve head (ONH) which together make up the ocular shell. Stresses and strains are generated within these tissues by the intraocular pressure (IOP), and abnormal mechanical responses to IOP-induced loading are thought to play an important role in diseases such as keratoconus and glaucoma. Measurement of the IOP-related deformation of the ocular shell is therefore needed to provide insight into these disease processes. In this work, ultrasound speckle tracking was used to characterize the ex vivo mechanical behavior of the ocular shell during controlled changes in IOP. The first study focused on the measurement of 3D strains in the human peripapillary sclera during IOP elevation from 10 to 19 mmHg. Our results showed that the peripapillary sclera experienced through-thickness compression and meridional stretch during inflation, while minimal circumferential dilation was observed. The maximum shear was primarily oriented in the plane created by the through-thickness and meridional directions and had a magnitude slightly larger than the first principal strain (i.e. meridional stretch). The tissue volume showed minimal overall change, confirming the near-incompressibility of the sclera. Substantial strain heterogeneity was present, with local high strain areas likely corresponding to structural heterogeneity caused by traversing blood vessels. The 3D strain characteristics provided new insight into the biomechanical response of the peripapillary sclera during physiological increases in IOP. Additional studies were carried out to measure the deformation of the ONH and peripapillary sclera simultaneously in response to IOP elevation. 2D ultrasound speckle tracking was used in conjunction with inflation testing of porcine and human eyes from 5 to 30 mmHg. The ONH and PPS showed overall posterior displacement in response to IOP elevation, with the displacements being much smaller for human eyes. Posterior displacement of the ONH was larger than and strongly correlated with the posterior displacement of the PPS throughout inflation testing. Scleral canal expansion was much smaller and leveled off more quickly than ONH posterior displacement as IOP increased. In porcine eyes, a clear pattern in strain distribution was seen with the largest strains located in the periphery of the anterior ONH. The strain distributions were more variable in human eyes, and scleral strains were not correlated with the strains within the ONH. Measurement of these deformation patterns contributed to the understanding of IOP-associated glaucoma susceptibility. Lastly, a novel ultrasound-based method called ocular pulse elastography (OPE) was developed to image corneal deformation during the naturally-occurring ocular pulse. The efficacy of the OPE method was evaluated using synthetic radiofrequency data as well as experiments on porcine and human donor eyes. Axial displacements of 0.5 µm and above were accurately measured with less than 10% error. Satisfactory speckle tracking was achieved for out-of-plane displacements up to 32 µm. Using synthetic RF data, the speckle tracking algorithm was proven to be able to detect strains down to 0.0001 axially and 0.00025 laterally with an error less than 10%. The corneal stiffness measured using OPE was shown to be highly correlated with the stiffness measured from standard inflation testing. Experiments in human donor eyes showed excellent repeatability. These results suggested the feasibility of the OPE method as a potential clinical tool for evaluating corneal biomechanics in vivo. Overall, these studies have demonstrated the ability of ultrasound speckle tracking to provide detailed measurements of the mechanical behavior of ocular tissue. This work has provided insight into the disease process of glaucoma and generated a promising method for detecting corneal disease.
Jun Liu (Advisor)
Cynthia Roberts (Committee Member)
Richard Hart (Committee Member)
171 p.
Biomechanics; Biomedical Engineering; Biomedical Research

Recommended Citations

Citations

  • Pavlatos, E. (2018). Ultrasound Speckle Tracking Methods to Study the Biomechanical Factors of Ocular Disease [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532039603048926

    APA Style (7th edition)

  • Pavlatos, Elias. Ultrasound Speckle Tracking Methods to Study the Biomechanical Factors of Ocular Disease. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1532039603048926.

    MLA Style (8th edition)

  • Pavlatos, Elias. "Ultrasound Speckle Tracking Methods to Study the Biomechanical Factors of Ocular Disease." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532039603048926

    Chicago Manual of Style (17th edition)

osu1532039603048926
294
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