Biomechanical Properties of the Bruch’s Membrane: An Atomic Force Microscopy Study

Abstract

Abstract: : Purpose: The exudative or wet form of age–related macular degeneration (AMD) is characterized by the choroidal neovascularlization (CNV) and is associated with rapid and severe vision loss. In CNV, new choroidal capillaries breach through the Bruch’s membrane and the retinal pigment epithelium (RPE). Changes in the integrity and the physical properties of the Bruch’s membrane have been linked to the AMD pathogenesis. However, the biomechanical properties of the Bruch’s membrane have not been previously studied. Methods: We have examined the structural and elastic properties of porcine Bruch’s membrane using atomic force microscopy (AFM) and electron microscopy (TEM and SEM). Results: For the AFM study, the unfixed cryo–sections of porcine retina–choriod (and the Bruch’s membrane) were simultaneously imaged with a light microscope and an AFM. The tissue elastic modulus in selected areas, including the Bruch’s membrane, was mapped by AFM nano–indentation. The Bruch membrane shows significant higher stiffness in comparison to the neighboring RPE cells and choroidal tissue. The sublayers of the Bruch’s membrane also exhibit distinct elastic characteristics: the Young’s moduli of the collagenous sublayers of Bruch’s membrane are in the range of 2–4 x 10⁶ Pa. The central elastin sublayer of the Bruch’s membrane is significantly softer than the adjacent collagenous layers. Conclusions: This study provides the first direct measurement of biomechanical properties of the Bruch’s membrane.

Keywords: Bruch's membrane • choroid: neovascularization • microscopy: confocal/tunneling