PRESENCE OF A CONTRACTILE CELL NETWORK IN THE HUMAN CHOROID

Immunohistochemical staining of choroidal whole mounts as well as seri al tangential sections and electron-microscopic investigation of 21 hu man donor eyes revealed a network of nonvascular alpha-smooth-muscle-a ctin-positive cells (NVSMC) in the entire choroid most densely arrange d in the posterior part of the suprachoroid of the submacular region. Ultrastructurally these cells present the typical structure of myofibr oblasts. Double labeling with desmin and smooth muscle myosin showed a positive reaction only in few of these cells. Posteriorly the NVSMC n et reaches the optic nerve, anteriorly it ends in the region of the vo rtex veins but does not continue into the ciliary muscle. In places, i ntimate contact between the contractile cells and the elastic fiber ne twork of the choroidal stroma and the perivascular sheaths is seen. Th e elastic net of the choroid is firmly connected with the posterior el astic tendons of the ciliary muscle. In the course of accommodation, t he ciliary muscle pulls this net foreward presumably influencing posit ion and diameter of the choroidal vessels. We assume that the network of NVSMC of the choroid counteracts the ciliary body movements during accommodation, thus guaranteeing the three-dimensional architecture of the choroid and the position of the retina, particularly in the macul ar region.