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Jonathan Mamou, Daniel Rohrbach, Quan V Hoang, Harriet O Lloyd, Sally A McFadden, Ronald H Silverman; Acoustic microscopy: an imaging tool to assess elastic properties of ocular tissues at the micrometer scale. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1719. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Assessing the mechanical properties of ocular tissue may provide insight into the mechanisms underlying a wide range of conditions. Scanning acoustic microscopy (SAM) is an ultrasound-based imaging modality that allows formation of quantitative 2D images of acoustical and mechanical properties of thin section of tissues at the micrometer scale. In this study, SAM was used to form images of bulk modulus and other mechanical parameters with a resolution better than 8 µm from human eyes and pig corneas.
Samples were obtained from 12 human donor eyes and 6 healthy pig eyes. Enucleated animal eyes were embedded in Tissue-Tek OCT compound, flash-frozen, and cryosectioned into 12-μm slices. Eye-bank eyes were immediately fixed in modified Davidson’s solution, embedded in paraffin, and sectioned into 12-μm slices. The SAM system was equipped with an F-1.16, 250-MHz transducer and had a 7-μm lateral focal-point beam width. Samples were raster scanned in 2D in 2-µm steps using high-precision motor stages. The amplified phase-resolved data were processed to yield estimates of speed of sound, acoustic impedance, attenuation, bulk modulus and mass density at each location.
SAM images of the bulk modulus and the acoustic attenuation of the angle region of a human eye are shown in Fig. 1. The co-registered histology image permits easy recognition of anatomical features. These images reveal that the bulk modulus within the central sclera is higher (2.73 ± 0.16 GPa) than that of the ciliary muscle (2.51 ± 0.08 GPa, p<0.001), which is higher than that of the trabecular meshwork (2.44 ± 0.05 GPa, p<0.001). Similarly, Fig. 2 reveals that the speed of sound in the epithelium of a pig cornea is lower (i.e., 1538 ±18 m/s) than in the stroma (1591 ± 28 m/s, p<0.001).
These studies demonstrate that SAM methods are capable of providing fine-resolution quantitative images that may be invaluable in investigating and understanding the biomechanical properties of ocular tissues in diseases where tissue elasticity is believed to play an important role, such as myopia, glaucoma, and keratoconus.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1: SAM images of the angle region of a human eye with co-registered histology photomicrograph. (I: iris, CP: ciliary process, CM: ciliary muscle, TM: trabecular meshwork, Sc: sclera)
Figure 2: Speed of sound image of a pig cornea
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