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W.H. Chan, A.A. Hussain, J. Marshall; Relationship Between Elasticity and Hydraulic Conductivity of Bruch’s Membrane . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3005.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine the relationship between elasticity and transport functions of ageing human Bruch’s membrane. Methods: A freshly isolated Bruch’s–choroid preparation was mounted in an open horizontal Ussing–type chamber such that the exposed curvature of Bruch’s membrane could be tracked by OCT. Hydrostatic pressure (range 5–30 mmHg) was applied from underneath and the corresponding change in membrane topography recorded. The resulting image analysis allowed calculation of arc–length subtended by Bruch’s in response to the applied pressure. Change in arc–length per unit applied pressure provided an index of elasticity. This analysis also provided a measure of the exposed surface area at a given pressure. Hydraulic conductivity (HC) was subsequently determined employing the same pressure range to induce flow. Calculations of HC using the original preparation area of a 4mm disc were designated ‘apparent’ and those utilising the OCT–derived surface area as ‘absolute’. Altogether, ten samples were examined in the donor range 22–89 years. Results: The elasticity index for Bruch’s–choroid preparations from macular regions ranged from 40 X 10–5 mm/Pa in the 22 year old to 4.31 X 10–5 mm/Pa in the 89 year old donor, the age–dependent decrease being linear with correlation coefficient r = –0.97 and significance p< 0.001. Similar changes were observed in the peripheral fundus, r = –0.54 and p< 0.001. The apparent hydraulic conductivity showed an exponential decline with age but the absolute hydraulic conductivity, taking into account the excessive surface area of the unstretched specimen during mounting, showed a linear decline with age, p< 0.001. Conclusions: The similar age–related demise in the elasticity and transport functions of Bruch’s suggests the presence of oxidative and cross–linking mechanisms that reduce the porosity of the fibrillar ultrastructure of the membrane. Advanced ageing changes associated with age–related macular degeneration (AMD) are therefore expected to severely compromise the integrity of structural and functional mechanisms that control transport rates through Bruch’s. The effect of such alterations on progression of the disease will be discussed.
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