Ultrastructure of iris muscles in diabetes mellitus.

Fine structure of iris muscles from 16 iris specimens in patients with diabetes mellitus were investigated by electron microscopy, and the results were compared with those of 10 specimens of senile cataract eye without diabetes of the corresponding age groups. Significant ultrastructural changes were extensively found at the regions of the dilator, sphincter muscles and of the nerves endings adjacent to them. To cytoplasm of the muscle cells was partly occupied by membraneous structures with concentric lamellar appearance. Cytoplasmic vacuolations were noted in the muscle cells. An increased number of the lipid droplets associated with pigment granules in the cells was found in all diabetic iris specimens. These three kinds of pathological changes (lamellar structure, vacuole, and lipid droplet) increased depending on the duration as well as the control of the disease. Althought these findings were noted both in the sphincter and dilator muscles, the latter seemed to be more severely affected. Degenerative nerve endings containing lamellar membraneous structures were observed in a few moderate cases. Nerve fibers frequently diminished in diabetic patients, especially in severe cases with longer duration together with poorly controlled cases. These findings suggest that diabetes involves the iris muscle cells as well as the nerves, and these changes might be a reason to produce a pupillary abnormality.