Microscopic Regional Changes in the Elastic Properties of Myopic Guinea Pig Choroid

Abstract

Purpose : In myopia development, the choroid provides an essential interface to translate retinal signals into scleral remodelling, but the mechanisms remain elusive. Using scanning acoustic microscopy (SAM) with 7-µm lateral resolution, we studied the dependency of the choroidal biomechanical properties in myopic guinea pigs (GP) eyes.

Methods : Thirteen 1-week old GPs were form-deprived for 1 week in the right eye to induce myopia while the left eyes were untreated. GPs were then euthanized and both eyes enucleated, flash-frozen and 12-µm thick serial cryosections were obtained in either a vertical (superior/inferior) or horizontal (nasal/temporal) orientation across the posterior pole. Specimens were scanned with a custom-made SAM with a 250-MHz transducer. Bulk modulus (K) and mass density (ρ) 2-dimensional maps were calculated from the SAM data via a frequency-domain approach. SAM maps were manually segmented to isolate choroidal stroma. To assess the biomechanical properties locally, the choroid was divided into adjacent regions of interest (ROIs) sized 0.2 mm laterally and 0.65 mm in anterior-posterior direction. Within each ROI, the mean and standard deviation of each parameter were calculated. The association between biomechanical parameters and region, myopia status and eccentricity relative to the optic nerve was assessed with linear regression analysis.

Results : Relative myopia ranged from -3 to -9.3D. Among control eyes, mean K in the temporal region was greater than the nasal (containing the central axis, +448 MPa, p< 0.001). Per 1 mm in increased eccentricity, nasal K increased by 70 MPa in control eyes (p=0.046). Temporal K decreased by 100 MPa in myopic eyes (p=0.015). Among myopic eyes, ρ was 0.03 g/cm³ greater in the superior vs. nasal region (p=0.04). In the nasal region, ρ was 0.03 g/cm³ greater in control vs. myopic eyes (p< 0.01). Per 1 mm in increased eccentricity, superior ρ increased by 0.01 (p=0.003) and nasal ρ by 0.01 g/cm³ in control eyes (p=0.02), whereas in myopic eyes, nasal ρ decreased by 0.03 g/cm³ (p=0.04) and temporal ρ by 0.04 g/cm³ (p< 0.001).

Conclusions : Choroidal stroma biomechanical properties display myopia-, eccentricity- and region-dependent differences. Our results support the idea that myopia development and possibly scleral remodelling depends on microstructural and biomechanical alterations in the choroidal stroma.

This is a 2021 ARVO Annual Meeting abstract.