Material Properties of Human Ocular Tissue at 7-µm Resolution

Abstract

Quantitative assessment of the material properties of ocular tissues can provide valuable information for investigating several ophthalmic diseases. Quantitative acoustic microscopy (QAM) offers a means of obtaining such information, but few QAM investigations have been conducted on human ocular tissue. We imaged the optic nerve (ON) and iridocorneal angle in 12-µm deparaffinized sections of the human eye using a custom-built acoustic microscope with a 250-MHz transducer (7-µm lateral resolution). The two-dimensional QAM maps of ultrasound attenuation (α), speed of sound ( c), acoustic impedance ( Z), bulk modulus ( K), and mass density (ρ) were generated. Scanned samples were then stained and imaged by light microscopy for comparison with QAM maps. The spatial resolution and contrast of scanning acoustic microscopy (SAM) maps were sufficient to resolve anatomic layers of the retina (Re); anatomic features in SAM maps corresponded to those seen by light microscopy. Significant variations of the acoustic parameters were found. For example, the sclera was 220 MPa stiffer than Re, choroid, and ON tissue. To the authors' knowledge, this is the first systematic study to assess c, Z, K, ρ, and α of human ocular tissue at the high ultrasound frequencies used in this study.

Improved High-Frequency Ultrasound Corneal Biometric Accuracy by Micrometer-Resolution Acoustic-Property Maps of the Cornea

“…However, such an effect never occurred, as illustrated in Figure 2 . From our previous SAM studies on ocular tissues, 23 – 25 , 36 we were able to maintain an approximately constant temperature with variations of less than 1°C even for scanning times as long as 40 minutes. The average scan area of the samples in this study was less than 4 mm 2 and required scanning times of less than 20 minutes.…”

Quantifying scattering from dense media using two-dimensional impedance maps

“…The method based on the 2DZM Fourier transform-based approach could be highly relevant to experimental and (pre-) clinical studies because accurate 2DZMs can be directly obtained using state-of-theart acoustic microscopy systems and algorithms. [31][32][33][34][35][36][37] Therefore, the proposed 2DZM approach could pave the way toward an easier and more complete understanding of ultrasound scattering in soft tissues, ultimately allowing a faster adoption of more reliable QUS methods for a wide variety of preclinical and clinical studies.…”

“…Another important axis of research is the use of experimentally obtained 2DZMs from acoustic microscopy. [31][32][33][34][35][36][37] The 2DZMs obtained from acoustic microscopy systems operating at very high frequencies (i.e., > 250 MHz) provide realistic data to evaluate the 2DZM approaches in real tissues or even in cell pellet biophantoms but remain time consuming. In addition, the spatial resolution of the 2DZMs is approximately the wavelength at the center frequency of the transducer used to collect the data, potentially limiting the bandwidth used for model inversion.…”

Ultrasound-Mediated Ocular Drug Delivery: From Physics and Instrumentation to Future Directions

“…This can result in imaging artifacts and invalid distance measurements. As an example, ultrasound is commonly used in ophthalmology for measuring eye axial length [ 47 ]; however, myopia, glaucoma, age-related macular degeneration, and dry eye disease are all ocular conditions that have been found to result in changes to the mechanical properties of the eye and therefore the speed of sound [ 48 , 49 ]. Normal speed of sound values for various ocular tissues, as reported by Thijssen et al [ 50 ], can be seen in Table 1 .…”