The fine structure of the iris (rhesus monkey and man) has been studied by electron microscopic examination of ultrathin sections.1 The results reported were in general agreement with those based on classical histologic methods2,3 and revealed in greater detail the structure of the cells, blood vessels and nerves of the stroma, the muscles, and the cells of the pigment epithelium. Such sections (about 0.025μ in thickness) are most suitable for the study of cellular structures, i.e., the structures composed of an abundance of macromolecular aggregates (microparticles, membranestructures, and filaments), but they provide very little information about components in low concentration. A good example of such components is found in the intercellular substances of the loose iris stroma. The technique of ultrathin sectioning has revealed the presence of collagen fibrils between the stroma cells, but their distribution and orientation with regard to other tissue components was not clear.
TOUSIMIS AJ, FINE BS. Ultrastructure of the Iris: The Intercellular Stromal Components. AMA Arch Ophthalmol. 1959;62(6):974-976. doi:10.1001/archopht.1959.04220060046008