Figure 10.

Throughout life, the components of extracellular matrix are regulated by a balance process with MMPs removing excess tissue while under the control of TIMPs (a). The presence of these two systems within Bruch's membrane is demonstrated in the histochemical preparations (b and c). Examples of disturbance of this regulatory mechanism have been identified particularly in Sorsby's fundus dystrophy where a genetic defect in TIMP-3 leads to a rapid increase in membrane thickness (d). By studying the movement of water through membranes as a function of age using a variety of different methods, it has been possible to derive both a graphic and mathematical model of resistance in the membrane and to demonstrate that the point of highest resistance occurs at the junction between the inner collagenous layer and the layer of elastin (RB) (e).