Age-related variation in the hydraulic conductivity of Bruch's membrane.

PURPOSE To determine whether alterations in local fluid dynamics are associated with aging of the Bruch's membrane-choroid complex. In the macula, such changes have been postulated as causative factors underlying some pathologic manifestations of age-related macular degeneration (AMD). METHODS The pressure-induced flow of physiological buffer through isolated human Bruch's membrane-choroid complex was measured using a modified Ussing chamber. Values of flow facilitated the calculation of hydraulic conductivity (flow per unit pressure), for individual complexes, which subsequently allowed for the development of an age-related profile. RESULTS In all specimens, flow across the Bruch's membrane-choroid complex was found to be directly proportional to the applied pressure, whereas hydraulic conductivity was independent of pressure over the range studied. The hydraulic conductivity of the complex exhibited an exponential decrease with increasing age of donor, the most rapid decline occurring during the first four decades of life. The age-related change was most pronounced in the macula, where hydraulic conductivity halved every 9.5 years, compared to a t1/2 for the periphery of 19 years. CONCLUSIONS The decline in the hydraulic conductivity of the Bruch's membrane-choroid complex with age implies a decreased capacity for the exchange of fluid between the choroidal and retinal pigment epithelial compartments. The relevance of these findings to the development of AMD is discussed.