Abstract
Myopia is caused by excessive axial eye length, which results in images focused in front of the retina. High (pathologic) myopia can lead to irreversible vision loss. The anatomic changes underlying excessive eye elongation likely occur in the eye wall (sclera), which becomes more flexible than in non-myopic eyes. In the present study, we employed a form-deprivation (FD), guinea pig myopia model and a scanning acoustic microscope (SAM) to study biomechanical properties in the sclera at microscopic levels. 12-µm-thick cryosections of sclera from 7 animals with varying levels of induced myopia were measured using a custom-built SAM. To induce myopia, each animal wore a translucent diffuser in front of the right eye from 4–12 days of life. Intraocular differences in refractive error ranged between −3.2 D to −9.3 D. The SAM was equipped with an F-1.16, 250-MHz transducer with a 160-MHz bandwidth and that provided a 7-µm lateral beam width. Maps of the speed-of-sound (c), acoustic impedance (Z), attenuation (a), Bulk modulus (K) and mass density (ρ) were derived from the frequency-domain representation of each recorded signal using a model-based approach. For the animal with the greatest myopia, values of K, ρ, α, c and Z in the control eye were significantly higher (p<0.05) at the inferior sclera. Moreover, K, c and Z were lower in the myopic eye in the inferior sclera. The results demonstrate the feasibility of assessing scleral material properties at very fine resolutions and indicate that myopia-related changes in those properties vary by location in the sclera. The fine-resolution quantitative images obtained in this study may be valuable in the investigation of the biomechanical properties of ocular tissues in diseases where tissue elasticity plays a role such as in myopia.
Published Version
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