Morphological features of iris fibroblasts in dilator muscle region.

Morphological features of iris fibroblasts in the dilator muscle region of the Japanese monkey iris were demonstrated by transmission and scanning electron microscopy. The iris fibroblasts in the dilator muscle region formed the boundary between the dilator muscle and the iris stroma. These iris fibroblasts were characteristically accompanied by numerous naked axonal varicosities containing synaptic vesicles on the dilator muscle side. When viewed by scanning electron microscopy, the stromal surface of the dilator muscle layer was incompletely covered by a single layer of iris fibroblasts. From the present morphological evidence, it is suggested that iris fibroblasts in the dilator muscle region play some role in the innervation of the dilator muscle.