Scanning electron microscopy of the monkey eye in miosis and mydriasis.

Abstract The structure of the iris, trabecular meshwork and the course and insertion of the zonular fibres have been examined in extreme miosis and maximal mydriasis of the monkey eye, using scanning electron microscopy. The iris showed pronounced differences in its posterior surface and in the shape of the posterior epithelial pupillary edge; in the course of the fibroblast-and melanocyte-processes in the pupillary area; and in the shape of the posterior epithelial layer and the course of vessels and melanocytes in radial as well as in tangential sections. Some difference was noticed in the width of the gaps at the anterior iris surface but no difference was seen in shape and density of the stromal collagen fibres. The trabecular sheets are spaced wider apart in miotic than mydriatic eyes, as seen through pores of meshworks that were left intact or meshworks that had been cut either circumferentially or meridionally; but a difference in the shape of the lamellar holes was not apparent. The ciliary processes frequently show a single crest in mydriasis and twin crests in miosis. The zonular fibres originate from the pars plana and insert into the lens by means of but two sets of fibres, anterior and posterior zonular fibres. These fibres do not cross; most fibres pass the ciliary processes though some fibres may adhere to valleys or crests being presumably vestigial of artefactual. The posterior zonular fibres insert into the posterior capsule forming a single circular rim, in front of the insertion of the anterior hyaloid membrane. The anterior zonular fibres insert circumferentially into the anterior capsule in two or three rows. All fibres insert axially to the equator of the lens and so-called equatorial fibres do not exist. With the present method, no difference could be demonstrated between the zonular fibres in miosis and mydriasis.