Fine structure and mechanics of the anterior border of the primate iris: a scanning and transmission electron microscope study.

The morphology of the anterior border of the primate iris has been examined by transmission and scanning electron microscopy. The results confirm that the anterior iris is composed of heavily pigmented melanocytes, fibroblasts, and a loosely arranged network of collagen fibres. The melanocytes are slender, elongate structures, which show some branching in the peripheral iris. They run parallel to the surface and are filled with spindle-shaped pigment granules which are oriented in the long axis of the cell. In the miotic state, the peripheral iris melanocytes form a dense, interlacing network. As the pupillary margin is approached, the angles between intersecting melanocytes diminish; the melanocytes appear to be parallel and in close contact with one another.During mydriasis, the peripheral iris melanocytes are compressed and pupillary components are found to intersect at angles greater than 90%. The superficial fibroblasts are flattened cells, closely applied to the underlying melanocyte processes and in the mydriatic iris form a resonably continous monolayer over the anterior iris surface. Iris pores are present, exposing the underlying melanocytes and stromal collagen. During miosis, the surface fibroblasts become attenuated and the pores increase in size and number. This paper demonstrates the value of the scanning electron microscope in presenting an accurate three dimensional model of the iris.