Neural influences on the iris of diabetic rats and effect of oculomotor nerve crush

Using an animal model where the pupil diameter of the eye in anaesthetized and dark-adapted rats serves as a parameter of autonomic function, we studied the functional recovery of the parasympathetic nerve fibres in the oculomotor nerve after a crush lesion in rats with streptozotocin-induced diabetes compared with normal controls. Prior to the crush lesion, diabetic rats develop significantly (P < 0.001) smaller pupils compared with controls, and this occurs early in the course of the diabetes mellitus. As the difference in pupil diameter between control and diabetic rats persists immediately after the crush lesion, when the nervous control of the pupil is entirely due to sympathetic nerves, we suggest that the reduction in pupil diameter is due to a sympathetic neuropathy. Furthermore, we show that the functional recovery of the parasympathetic input to the iris after a crush lesion of the oculomotor nerve is not as good in diabetic rats as it is in normal control rats.