Some histological aspects of the structure of the connective tissue system and its relationships with the blood vessels in the human orbit.

The connective tissue septa in the human orbit are organized in a constant and characteristic fashion. In the collagen fibre meshwork of the septa, anteroposteriorly directed collagen fibre bundles are relatively rare. The number of smooth muscle cells present in a septum depends on the orbital level explored. In the apical region only few of these cells are found, at eye-ball level they are more numerous. No further regularity in distribution of smooth muscle cells in the septa is present. All connective tissue septa contain elastic fibres. Blood vessels and connective tissue form an integrated system. The venous walls merge with the fibrous structure of the septa; the arteries only make contact with the septa when they perforate them. In doing so, the arteries mainly run between the septal fibre bundles, only loosely connected to some of them. The microvascular system is predominantly confined to the adipose tissue compartments. The interrelationships of the vascular system and the connective tissue system are likely to be important factors in controlling and regulating orbital blood-flow. In addition, the well-defined morphological organization of the connective tissue in its interrelationships with the vascular system might serve a mechanical regulating function by both allowing and restricting certain eye-ball movements. For these functions, the physico-chemical properties of the connective tissue system and the microstructure of the vascular system are probably of considerable interest. Thus, the highly organized architecture of the connective tissue system in the human orbit together with its intricate interrelationships with the vascular system, might prove to be important for mechanical as well as metabolic purposes and so have consequences for interventions, diagnostic or surgical, in the orbit.