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Cameron Hoerig, Kazuyo Ito, D.Renick Lee, Sally A McFadden, Quan V Hoang, Jonathan Mamou; Relationships between mechanical and microstructural tissue properties in the posterior sclera. Invest. Ophthalmol. Vis. Sci. 2021;62(8):3271.
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© ARVO (1962-2015); The Authors (2016-present)
Scleral microstructural and mechanical properties can be affected by myopia. Second harmonic generation (SHG) microscopy can glean information about collagen microstructure whereas scanning acoustic microscopy (SAM) is sensitive to bulk mechanical tissue properties. This study used SHG and SAM to investigate the relationship between tissue microstructure and mechanical properties in myopic guinea pig (GP) eyes.
One week of form-deprivation myopia was induced in the right eyes of four 1-week-old GPs. Left eyes were untreated controls. GPs were euthanized at 14-days of age; both eyes were enucleated, slowly fresh frozen, and stored at -80°C. Whole unfixed globes were vertically cryosectioned every 12μm. Posterior regions of adjacent tissue sections were scanned with SAM (250-MHz transducer) or SHG (860nm excitation wavelength). Maps of bulk modulus (K), mass density (ρ), sound speed (c), and acoustic attenuation (α) were estimated from SAM data using a Fourier-domain, model-based inverse method. A curvelet-based analysis method operated on SHG images to estimate collagen fiber length (L), straightness (S), orientation (O), and width.
Differences in mean material properties between control and myopic (-5.54, -3.21, -9.29, and -7.13 D) eyes were Δc=-17.55±5.81 m/s, ΔK=-0.11±0.2 GPa, Δρ=-0.01±0.002 g/cm3, and Δα= -0.37±0.19 dB/MHz/cm (all p<0.05). Comparing estimated collagen fiber characteristics to material parameters, the standard deviation of O (σO) most strongly correlated with ρ and α (r=0.79,p<0.0001 and r=-0.75,p<0.0001) while S was most strongly correlated with c and K (r=-0.63,p=0.001 and r=-0.52,p=0.01). Associations were weak between control eye L and σO with distance from the optic nerve head (ONH, r=-0.64,p=0.05 and r=-0.43,p=0.22) whereas myopic eye L and σO were positively correlated with distance (r=0.86,p=0.001 and r=0.83,p=0.003). Similarly, K,c, and α did not vary with distance in control eyes (all p>0.5) but increased further from the ONH in myopic eyes (r=0.83,0.9,0.72,p<0.001).
Bulk mechanical parameters measured with SAM correlated with collagen fiber microstructure, particularly fiber orientation. Results of this study demonstrate the effect of myopia on scleral tissue microstructure and subsequent changes in bulk tissue mechanical properties. SAM may be effective for assessing microstructural and mechanical changes associated with myopia.
This is a 2021 ARVO Annual Meeting abstract.
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