Presence of a contractile cell network in the human choroid.

Immunohistochemical staining of choroidal whole mounts as well as serial tangential sections and electron-microscopic investigation of 21 human donor eyes revealed a network of nonvascular alpha-smooth-muscle-actin-positive cells (NVSMC) in the entire choroid most densely arranged in the posterior part of the suprachoroid of the submacular region. Ultrastructurally these cells present the typical structure of myofibroblasts. Double labeling with desmin and smooth muscle myosin showed a positive reaction only in few of these cells. Posteriorly the NVSMC net reaches the optic nerve, anteriorly it ends in the region of the vortex veins but does not continue into the ciliary muscle. In places, intimate contact between the contractile cells and the elastic fiber network of the choroidal stroma and the perivascular sheaths is seen. The elastic net of the choroid is firmly connected with the posterior elastic tendons of the ciliary muscle. In the course of accommodation, the ciliary muscle pulls this net foreward presumably influencing position 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 macular region.